Allophaiomys and the Age of the 

Olyor Suite, Krestovka Sections, Yakutia 

U.S. GEOLOGICAL SURVEY BULLETIN 2037 

DE. CR .ICETO 

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Allophaiomys and the Age of the Olyor Suite, 

Krestovka Sections, Yakutia 

By CHARLES A. REPENNING 

U.S. GEOLOGICAL SURVEY BULLETIN 2037 

Microtine history indicates mosaic evolution and complex 

dispersal patterns around the Northern Hemisphere; 

by reflecting this history and evaluating stage of population 

evolution, microtine biochronology can discriminate time 

periods as brief as 5,000 years 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1992 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

For sale by USGS Map Distribution 

Box 25286, Building 810 

Federal Center 

Denver, CO 80225 

Any use of trade, product, or finn names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

Library of Congress Cataloging-in-Publication Data 

Repenning, Charles A., 1922-

Allophaiomys and the age of the Olyor Suite, Krestovka sections, Yakutia I by Charles A. Repenning. 

p. em. -(U.S. Geological Survey bulletin ; 2037) 

Includes bibliographical references. 

1. Allophaiomys pliocaenicus-Russia-Yakutia. 2. Paleontology-Russia-Yakutia. 3. PaleontologyPleistocene. 4. Geology, Stratigraphic-Pleistocene. I. Title. ll. Series. 

QE882.R6R48 1993 

569'.323-dc20 92-27844 

CIP 
CONTENTS 

Abstract .............................................................................................................................. .. 

Introduction ......................................................................................................................... . 

Acknowledgments ............................................................................................................. .. 

Explanation of the problem ................................................................................................ . 

Conventions ........................................................................................................................ . 

1 

2 

4 

4 

7 

Vernacular nomenclature ................ .... ......... ... ....... ....................... ......... ......... ......... .. 8 

Time scales ................................................................................................................. 9 

Dental morphology ...................................... .. ... ......................................................... 10 

Variability and evolution ..................................................................................................... 12 

Variation and biochronology ................ ..................... ....................... ........ ...... ........... 17 

Multiple origins ................................................................................................................... 18 

Classification .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . .. .. . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . .. . . . . . . . . . . . .. . . . . . . . ... . . . . . . .. . . . . . . . .. 21 

Systematics: Philosophy, problems, applications .......... ...................... .... .. .. .. ......... ......... ... 24 

Tribe Arvicolini, Kretzoi, 1954 ................................................................................. 24 

Genus Allophaiomys Kormos, 1932 .................................................................... 25 

"Typical" Allophaiomys .... ........................................................................... 25 

Allophaiomys pliocaenicus Kormos, 193~ ............................................... 25 

Allophaiomys from the Java fauna............................................................... 32 

Allophaiomys from the SAM Cave faunas .................................................. 33 

Allophaiomys from the Wellsch Valley fauna ......... ........... ........... .............. 36 

Allophaiomys from the Cheetah Room fauna ................ ... ................ ........... 38 

Allophaiomys from the Hanover Quarry Fissure fauna ........ .. ..................... 41 

Allophaiomys from the Cumberland Cave fauna ..... .. ............. ............ ......... 42 

Other North American localities .................................................................. 43 

Tribe Microtini, Simpson, 1945 ............................................................................... .. 

Genus Lasiopodomys Lataste, 1887 .................................................................. .. 

"Typical" Lasiopodomys ........................................................................... .. 

Lasiopodomys from the Anza-Borrego Desert ........................................... . 

Lasiopodomys from the Cheetah Room fauna ............................................ . 

? Lasiopodomys from the Hanover Quarry Fissure fauna .......................... .. 

Lasiopodomys from the Cum~rland Cave fauna ....................................... . 

Lasiopodomys from the County Line fauna ............................................... .. 

Lasiopodomys from the Locality CRH--47 fauna ...................................... .. 

Genus Microtus Shrank, 1798 ........................................................................... .. 

"Typical" Microtus ..................................................................................... . 

Microtus from the Hansen Bluff faunas ..................................................... . 

Microtus from the Cumberland Cave and Locality CRH--47 faunas ........ .. 

Microtus from the Trout Cave No. 2 fauna ................................................ . 

Genus I..emmiscus Thomas, 1912 ....................................................................... . 

"Typical" I..emmiscus .................................................................................. . 

Genus Proedromys Thomas, 1911 ...................................................................... . 

"Typical" Proedromys ................................................................................ . 

Tribe Pitymyini, Repenning, 1983 ............................................................................ .. 

Genus Pitymys M'Murtrie, 1831 ........................................................................ .. 

"Typical" Pitymys ....................................................................................... . 

Genus Pedomys Baird, 1857 ............................................................................... . 

Pedomys llanensis Hibbard, 1944 ............................................................... . 

Genus Terricola Patio, 1867 ............................................................................... . 

"Typical" Terricola .................................................................................... . 

44 

46 

46 

50 

51 

52 

52 

54 

54 

56 

56 

61 

62 

63 

64 

64 

65 

65 

65 

67 

67 

68 

70 

71 

71 

III 
IV CONTENTS 

Systematic summary ............................................................................................................ 72 

Provinciality ........................................................................................................................ 74 

Correlation summary ........................................................................................................... 80 

Age of Krestovka Olyor and Cape Deceit faunas ............................................................... 82 

Olyor fauna, Western Beringia .................................................................................. 82 

Locality KL0-8 ................................................................................................... 82 

Locality KL0-9 .................................................................................................... 84 

The Cape Deceit fauna, Alaska ................................................................................. 88 

Conclusion ........................................................................................................................... 89 

References cited................................................................................................................... 91 

Index..................................................................................................................................... 97 

FIGURES 

1. Index map of Northern Hemisphere north of Tropic of Cancer........................................................................... 3 

2. Chart showing different age assignments of formations in the Krestovka Sections ............................................ 8 

3-13. Drawings showing occlusal surface of cheek teeth of: 

3. Allophaiomys pliocaenicus Kormos from Betfia-2 (Puspokfurdo), Romania ........................................... 26 

4. Phaiomys leucurus Blyth from Ladak, Kashmir ........................................................... ............................. 29 

5. Allophaiomys sp. from Java fauna, South Dakota ........................................................................................ 33 

6. Allophaiomys n. sp. from SAM Cave, New Mexico ....................................................................... ............. 35 

7. Allophaiomys sp. and Microtus sp. from Wellsch Valley fauna, Saskatchewan; 

Allophaiomys from Hansen Bluff core, Colorado ............................................ ............................................ 37 

8. Allophaiomys sp. cf. pliocaenicus (advanced) from the Cheetah Room fauna, West Vrrginia .................... 40 

9. Allophaiomys guildayi from Hanover Quarry Fissure fauna, Pennsylvania.................................................. 42 

10. Microtus and Terricola from Anza-Borrego Desert and Irvington fauna, 

California, with explanation of dental terms ................................................................................................ 45 

11. l.Asiopodomys spp. ........................... ............................................................................................................ 49 

12. Microtus spp. ................................................................................................................................................ 57 

13. Pitymys spp. and Terricola spp. .................................................................................................................... 69 

14. Phylogenetic diagram of genera ofMicrotini and Pitymyini herein discussed...................................................... 74 

15-17. Drawings showing occlusal surface of cheek teeth of: 

15. l.Asiopodomys sp. from Olyor Ilia Locality KL0-8, Krestovka Sections .................................................. 83 

16. Lasiopodomys and Microtus from Olyor Ilia Locality KL0-9, Krestovka 

Sections, and Lasiopodomys from Karay-Dubina fauna, Ukraine .............................................................. 85 

17. Lasiopodomys deceit ens is from Cape Deceit fauna, Alaska ....................................................................... 90 

TABLE 

1. Inferred ages, significant faunal characteristics, and availability of external age control of localities discussed ......... 81 
ALLOPHAIOMYS AND THE AGE OF THE OLYOR 

SUITE, KRESTOVKA SECTIONS, YAKUTIA 

By CHARLES A. REPENNING 

ABSTRACT 

Upper Pliocene and lower Pleistocene sediments along 

the Krestovka River, near its junction with the Kolyma River 

in eastern Yakut A.S.S.R., northeastern Siberia, provide two 

records of environmental deterioration in the Arctic Ocean 

Borderland. Both records precede major continental glaciation elsewhere in the Northern Hemisphere. The Olyor Suite 

of the Krestovka Sections contains the younger of these two 

records, but its age has been debated. Clarification of its age 

is of importance to early Pleistocene terrestrial history in the 

Arctic Ocean Borderland and in adjacent temperate regions 

of the Northern Hemisphere. 

During the late Pliocene and Pleistocene the most timediscriminate fossil mammals are those microtine rodents that 

derive from the genus Allophaiomys of the microtine tribe 

Arvicolini. Most of these derived taxa belong to the tribes 

Microtini and Pitymyini. The history of usage of the genus 

Allophaiomys indicates that the definition of the genus has 

not been uniform and that some current definitions are too 

broad, overlapping the definition of derived taxa. The use of 

varied nomenclatures has resulted both in differences of 

opinion regarding the age of the Olyor Suite of the Krestovka 

Sections and in confusion of other correlations throughout 

the Northern Hemisphere. 

Primarily through examples from North American fossil faunas, the history of Allophaiomys and its derived genera 

is outlined, and taxa are defined uniformly. The adoption of 

these uniform defmitions is recommended; other definitions 

of these genera cannot be applied without altering generic 

concepts that are based upon the type populations, and without uniform definitions biochronologic correlation of events 

in the evolutionary history of the subfamily Arvicolinae is 

impossible. 

At present, the most accurate Northern Hemisphere terrestrial correlations for approximately the last 2 million 

years rely almost exclusively on this history of Allophaiomys 

and its derivatives, and these correlations cannot be realized 

without uniformity of nomenclature. Review of the global 

record of these microtine rodents indicates that those found 

in the older part of the Olyor Suite of the Krestovka Sections 

cannot be as old as the Olduvai Normal-polarity Subchron 

(not as old as 1.67 Ma) but that they are older than the 

Jaramillo Normal-polarity Subchron (older than 0.97 Ma). 

An age possibly as great as 1.5 million years is suggested for 

the onset of deposition of the Olyor Suite in the Krestovka 

Sections of Y akutia. 

The provincial history of the evolution of these lineages 

in at least eastern Asia must become much better known 

before this age approximation can be refined. Worldwide, 

the determination of this history is made difficult by the 

essential lack of external time control between the Olduvai 

and Jaramillo Normal-polarity Subchrons of the Matuyama 

Reversed-polarity Chron. This is a period of reversed geopolarity approximately as long as the Brunhes Normal-polarity 

Chron, containing few documented polarity events that 

might serve as temporal subdivisions. 

Greater integrative understanding of the provincial history of the microtines in the United States indicates that a 

potential exists for inferring age assignments that differ as 

little as 5,000 years. Establishing this age precision requires 

thorough evaluation of the stage of evolution of fossil populations, which in tum requires sufficiently large samples 

possessing some external age control, to provide temporal 

calibration of the evolutionary history. Between lineages 

deriving from Allophaiomys the rates. of evolution can vary 

greatly, and the accuracy of biostratigraphic correlation varies directly with the rate of evolution. The rate of evolution 

in nominally identical lineages may also vary between faunal 

provinces; therefore accurate correlation, again, requires an 

understanding of provincial history. 

In addition to radiometric age determination, external 

age control is recognized throughout the Northern Hemisphere in sufficiently well documented (1) paleomagnetic 

determinations, (2) climate change trends, (3) mammalian 

dispersal events, and (4) known history of other mammalian 

types including other associated microtine rodents. When 

used herein, the sufficient documentation of these external 

age controls is explained, defended, and integrated. 

The estimation of the age of the Olyor Suite in the 

Krestovka Sections of Yakutia requires that the timecalibrated history of evolution and of dispersal throughout 

the Northern Hemisphere be understood for those microtines 

that have been found as fossils within that depositional unit. 

This requires that they be correctly identified. From 1977 to 

the present many publications have listed the genus 

Allophaiomys as being present in the Olyor faunas, imparting a rather specific age suggestion that has been interpreted 
2 ALLOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

to be more than 2.1 million years for the oldest fauna. But 

this genus is not present in the Olyor Suite, and what was 

called Allophaiomys has a different age significance that, at 

this location, cannot be older than an estimated 1.4 million 

years. Paleomagnetic polarity of the section, in concert with 

the age implication of the microtine rodents, indicates that 

the Olyor cannot be as old as 1.67 million years. 

INTRODUCTION 

In 1966 fossiliferous upper Pliocene and Pleistocene 

continental deposits were discovered by A. V. Sher in the 

lower part of the drainage basin of the Kolyma River of 

northeastemmost Yakut A.S.S.R. (fig. 1), the Kolyma Lowlands. The region is located at approximately lat 69° N ., long 

160° E., and has been continuously studied since 1966 by 

scientists from the Academy of Sciences of the Union of 

Soviet Socialist Republics, Moscow State University, and 

other Soviet institutions (Sher and others, 1979). The 

Kolyma River is in the western part of Beringia, a vast area 

covering the Arctic Ocean Borderland in. northeastern 

Siberia and northwestern North America that has never been 

covered by continental glaciation. From the Kolyma River, 

Beringia extend~ eastward to the headwaters of the Yukon 

River in northern Yukon Territory, Canada. 

The Krestovka Sections (locality 31, fig. 1), located 

along the Krestovka River near its junction with the Kolyma 

River, contain two records of climatic deterioration. These 

periods of climatic deterioration are recorded in continental 

deposits, the deposition of which ended with the development of major continental glaciation elsewhere in the Northem Hemisphere. The termination of continental deposition 

with the development of major continental glaciation 

appears in several records of the Arctic Ocean Borderland, as 

well as in lower latitudes, and seems to be related to eustatic 

lowering of sea level (resulting in a lowering of terrestrial 

base levels on adjacent lands). 

The older stratigraphic units of the Krestovka Sections 

have been described as the Begunov Suite of probable early 

Pliocene age and the Kutuyakh Beds of late Pliocene age 

(Sher and others, 1979). (The terms "suite" and "beds" are 

approximately equivalent to "formation" in North American 

literature according to Giterman and others, 1982.) The 

Begunov Suite is still not certainly dated but is now thought 

more likely to be of late middle Pliocene age, and to have 

been deposited during the Gauss Normal-polarity Chron on 

the basis of its normal polarity and the similarity of its flora 

to that from Ocean Point, Alaska (Nelson and Carter, 1985, 

1991; Repenning and Brouwers, 1992). The Kutuyakh Beds 

are of late middle and early late Pliocene age, as originally 

interpreted; they were deposited during the last of the Gauss 

Chron and into the beginning of the Matuyama Reversedpolarity Chron (Sher and others, 1979). 

The Begunov Suite and the Kutuyakh Beds, between 

less than 3 and about 2.4 million years old (Sher and others, 

1979; Repenning and Brouwers, 1992), record both a reduction in the variety of arboreal vegetation and a decrease in its 

total abundance. This record ends with sparse forest-tundra 

and the oldest known permafrost in the lower latitudes of the 

Arctic Ocean Borderland (Sher and others, 1979). In the 

Krestovka Sections, permafrost frrst appears in the younger 

part of the Kutuyakh Beds, at the time when the beginning of 

continental glaciation is conspicuously indicated elsewhere 

in the Northern Hemisphere. The age of this part of the Krestovka Sections has not been debated. 

In contrast to the less severe conditions beginning the 

earlier climatic record, the climatic record in the overlying 

Olyor Suite of the Krestovka Sections begins with sparse 

forest tundra and deteriorates to full tundra, more severe than 

the taiga that exists in the Krestovka area today. During the 

coldest period recorded by the fossil flora in the Olyor Suite, 

the reversed paleomagnetic polarity recorded in the older 

part of the Olyor changes to normal. The age of the Olyor 

Suite of the Krestovka Sections and the identity of the 

normally polarized event constitute the second subject of 

discussion in this report. 

An erosional unconformity separates the Kutuyakh 

deposits from the overlying Olyor Suite in the Krestovka 

Sections. Different opinions about the age of the Olyor Suite 

have been published, with consequent variation in the opinions about the time encompassed by this unconformity. Sher 

and others (1979), strengthened by Sher (1986), suggested 

. that deposition of the Olyor Suite, as recorded in the Krestovka Sections, began during the last part of the Matuyama 

Chron and continued into the Brunhes Chron. Similarly, 

Virina and others (1984) indicated that deposition of the 

Olyor Suite in its type section (some 150 km1 (93 mi) north 

of the Krestovka Sections) began before the Jaramillo 

Normal-polarity Subchron and continued into the Brunhes. 

No non-biochronologic data (external to the mammalian 

history) exist for estimating the age of the oldest (preJaramillo) part of the type Olyor, and the base of the type 

Olyor is not exposed. 

Repenning ( 1984) indicated that the history of microtine rodents, in combination with the history of climatic 

changes recorded by Sher and others (1979), suggested that 

deposition of the Olyor Suite must have begun more than 2 

million years ago. This interpretation, based upon published 

faunal lists, is now known to be wrong for two reasons. First, 

it has recently been recognized that the application of 

taxonomic names (particularly Allophaiomys) in the identification of microtines from the Olyor Suite differs greatly 

between the present author and others who have examined 

this fauna. Second, new information about the global history 

1 Note that in this report the primary system of measurement unitsthe unit cited ilrst-is that of the country from which the data were gathered 

and published. North American data were given nrst in inches, feet, and 

miles; European and northeastern Asian data were given ilrst in metric. 

Conversion to the other system is given in parentheses. 
INTRODUCTION 3 

Figure 1. Index map of Northern Hemisphere north of Tropic of Cancer showing localities mentioned. 1, Karay-Dubina, Ukraine. 2, 

Shamin, Russia. 3, Betfia-2 (Puspokfurdo), Romania. 4, Zuurland Borehole, Holland. 5, Villany-5, Hungary. 6, Holstejn, Czechoslovakia. 

7, Mas Rambault and Balaruc, France. 8, Huangkan and Choukoutien (CKT)-18, P.R.C. (People's Republic of China). 9, Wellsch Valley, 

Saskatchewan. 10, Java, South Dakota. 11, Cumberland Cave, Maryland. 12, Ladak, Kashmir. 13, Kamyk, Poland. 14, Valerots, France. 15, 

Hansen Bluff, Colorado, and SAM Cave, New Mexico. 16, Hanover Quarry Fissure, Pennsylvania. 17, Cheetah Room, West Virginia. 18, 

Cudahy, Nash, and Aries, Kansas. 19, Fyllan Cave, Texas. 20, County Line, Dlinois. 21, Anza-Borrego Desert, California. 22, Irvington, 

California. 23, Cape Mendocino, California. 24, Cape Deceit, Alaska. 25, Localities CRH-47, CRH-64, and CRH-11, Yukon Territory. 26, 

Conard Fissure, Arkansas. 27, Gongw.angling, P.R. C. 28, Georgia, U.S.A. 29, Ft. Pierre, South Dakota. 30, Northeast Mongolia, P.R.C. 31, 

Krestovka Sections, Kolyma Lowlands, Yakutia. 32, Germany. 33, Froman's Ferry, Idaho. 34, Razdolie, Western Siberia. 35, Leman Basin, 

Switzerland. 36, Minchow, Kansu, P.R.C. 37, Magruder Mtn., Nevada (near Deep Spri~gs, California). 

of these rodents, some not· previously published, indicates 

that the age of the Olyor must be closer to the age of the latest 

Matuyama and early Brunhes Chrons, as was originally 

claimed by Sher and others (1979). Consequently, it is 

unlikely that the oldest faunas in the Olyor Suite of the Krestovka Sections are much older than 1.5 million years. The 

unconformity below the Olyor Suite thus must be about 1 

million years long, lasting from about 2.4 to about 1.5 

million years ago. The time of the first significant continental glaciation of the Northern Hemisphere, peaking about 2.1 

million years ago, does not seem to be recorded in the deposits of the Krestovka Sections. 

Incorporation and interpretation of these revised data 

indicate that the oldest deposits in the Olyor Suite in the 

Krestovka Sections are, possibly, about the same age as 

those of the type Olyor 150 km to the north, and that 
4 AUOPHAIOMYS AND THE OLYOR SUITE, Y AKUTIA 

deposition was interrupted, in the Krestovka Sections, by a 

second unconformity in the normally polarized part of the 

Olyor Suite. This unconformity represents at least the 

150,000 years of reversed polarity between the Jaramillo 

and the Brunhes and includes the time of the beginning of 

deposition of the Nebraskan tills in the United States. However, the possibility that the oldest normal polarity represents the Jaramillo event is not supported by known 

micro tine and climatic history. Explanation of the age significance of the microtine faunas related to this oldest normal polarity is the first and major subject of discussion in 

this report. The second and shorter sub.!5ct of discussion is 

the application of this biochronologic mformation to the 

faunas of the Krestovka Olyor Suite, and the consideration 

of polarity patterns and climatic trends involved, to determine the age of the oldest part of .the formation. 

ACKNOWLEDGMENTS 

This is a summary of the global record of the genus 

Allophaiomys and of its derivative genera, as well as an 

application of this record to the interpretation of the age of 

the Olyor Suite of the Krestovka Sections in Y akutia. In its 

compilation, advice and specimens have been provided by 

many individuals. I would particularly like to acknowledge, 

with thanks, the help of Oldrich Fejfar (Prague, Czechoslovakia), Kazimerz Kowalski (Krakow, Poland), Wighart von 

Koenigswald (Bonn, Germany), Vladimir S. Zazhigin and 

Alexy Tesakov (Moscow, Russia), Shaohua Zheng (Beijing, 

People's Republic of China), Anthony Barnosky (Berkeley, 

California), Karel Rogers (Alamosa, Colorado), Russell 

Graham (Springfield, Illinois), Lawrence Flynn (Cambridge, 

Massachusetts), and Robert Martin (Rome, Georgia). All 

have provided thoughtful discussion about the methods of 

evaluating variability as well as specimens in illustration. 

Thanks are also extended to the professionals in charge 

of the collections from which specimens for the study were 

borrowed. These include the following institutions (with 

their acronyms): Geological Institute, Academy of Sciences 

of the Union of Soviet Socialist Republics, Moscow (GIN); 

Hungarian Natural History Museum, Budapest (HNHMB); 

National Museum of Natural History [United States], Washington (USNM); Carnegie Museum of Natural History, 

Pittsburgh (CM); Illinois State Museum, Springfield (ISM); 

National Museums of Canada, Ottawa (NMC); Natural History Museum of Los Angeles County, California (LACM); 

University of California Museum of Paleontology, Berkeley 

(UCMP); University of California Museum of Vertebrate 

Zoology, Berkeley (UCMVZ); and the University of Alaska, 

Fairbanks (UA). Specimens not credited to the above 

acronyms are in my collection in the Denver, Colorado, 

offices of the U.S. Geological Survey. 

Andrei V. Sher of the Paleontologic Institute, Academy 

of Sciences of the U.S.S.R., Moscow, was the key to the 

understanding of the age of the Olyor Suite of the Krestovka 

Sections in the Kolyma Lowlands of Y akutia, western 

Beringia. He made this discussion of the age of the Olyor 

Suite possible by inviting me to visit Moscow and review the 

fossil microtines from there; without this opportunity I 

would never have guessed their true identity. 

Vladimir S. Zazhigin of the Geological Institute of the 

Academy of Sciences of the U.S.S.R., who studied the specimens from Y akutia, kindly showed and discussed his entire 

collection from Y akutia and from other Asian localities for 

nearly 2 weeks and otherwise offered me his hospitality. His 

student, Alexy Tesakov, greatly facilitated this examination 

and review, thanks to his ability to speak English and to his 

knowledge of microtine rodents. 

R. Farley Fleming, USGS, spent many hours discussing 

with me the philosophy of various evolutionary theories and 

of classification, with the detachment that only a paleobotanist could have. Although I do not believe that he would 

agree, I have concluded that the present report is not concerned with evolutionary theories, but only with the facts of 

evolution as found in the fossil record. To those who disagree, I can only apologize for failing to find significance in 

theory. 

Anthony D. Barnosky, Thomas M. Bown, William A. 

Bryant, Oldrich Fejfar, Patricia A. Holroyd, Andrei V. Sher, 

Alexy Tesakov, and Alisa J .. Winkler were kind enough to 

review the manuscript-a major effort because of its complications. Kazimerz Kowalski also made helpful comments. 

Lorna Carter, editor for the U.S. Geological Survey, again 

has earned my gratitude for identifying wording that could 

be more understandably phrased. 

I think that none of these friends would appreciate my 

suggesting that they agreed with me. 

This report was completed with the help of a Gilbert Fellowship from the U.S. Geological Survey, project 

1-9590--09250 from April 1991 to April 1992. Without 

this support this synthesis, which was begun in 1990, 

might not yet be completed. The U.S. Geological Survey also provided my salary and $350 to help pay for 

my trip to Moscow in September 1990. 

EXPLANATION OF THE PROBLEM 

Different opinions previously put forth (fig. 2) regarding the age of the Olyor Suite of the Krestovka Sections 

resulted from unrecognized differences in the operational 

definition used by specialists when dealing with Kormos' 

(1932) genus Allophaiomys. These differences have a bearing on the definitions of the genera Microtus and 

Lasiopodomys, genera of the tribe Microtini that derive from 

Allophaiomys as shown by Chaline (1966). What some 

would refer to these genera, others would call Allophaiomys. 

In Chaline's usage, all three genera, Allophaiomys, 

Lasiopodomys, and Microtus (as well as the tribes Microtini, 

Pitymyini, and part of the Arvicolini recognized here) are 

included in the single genus Microtus. V.S. Zazhigin and 

A.V. Sher, the principal Russian authorities on the Krestovka Sections and their microtine rodents, have considered 
EXPLANATION OF THE PROBLEM 5 

Allophaiomys as a genus separate from Microtus since at 

least 1976. The present author has considered both Allophaiomys and Lasiopodomys as genera distinct from Microtus 

since approximately the same time. Fundamentally, these 

differences in the definitions of these taxa have resulted in 

the differing interpretations of the age of the Olyor Suite. 

Secondarily, different interpretations of the evolutionary history of the taxa further dictated different age assignments. In 

the present report, the three genera are considered separate, 

representing two different tribes. 

The problem relates to the concept of a type specimen. 

All students of microtine rodents recognize that all individuals in a type population of a microtine species do not exactly 

match the type specimen; even Kormos (1932) realized this, 

for he illustrated more than one individual (to ·show variation), even though he selected a type specimen for Allophaiomys pliocaenicus. Anyone using his specific name A. 

pliocaenicus is forced to guess how much individual variability can be acceptable-unless that person has the opportunity to examine the type population in Budapest. In fact, 

this type collection no longer completely exists, because representative specimens have been removed from it and 

donated to other collections throughout Europe. However, 

enough remain in the type sample to give a good idea of the 

range of variability. 

It is in deciding upon the acceptable range of variability 

that definitions begin to vary. The only recourse is to return 

to the type population sample and determine the "typical" 

variability. 

In association with V .S. Zazhigin, Sher and others 

(1979) and Sher (1986) had reported Allophaiomys in the 

older deposits of the Krestovka Olyor Suite as high as the 

earliest record of Microtus. Above this horizon only Microtus is reported from the formation. Just above the horizon of 

the first Microtus, the paleomagnetic polarity changes from 

reversed to normal. These authors placed great temporal significance on this change in the microtine fauna and its position immediately below the polarity change. They cited 

evidence from Markova ( 1982) that Microtus replaced Allophaiomys in the Ukrainian Karay-Dubina fauna that is older 

than reversed deposits underlying the Brunhes Normalpolarity Chron. The Karay-Dubina fauna was assumed to be 

younger than the Jaramillo event, but this event was not 

recorded in the sediments. Markova's presumed replacement 

of Allophaiomys by Microtus in a fauna presumably between 

the Jaramillo and the Brunhes was the strongest reason for 

Zazhigin and Sher to assign the same age to what they presumed to be the same replacement of genera in the Olyor, 

and the first normal polarity immediately upsection from it 

was, accordingly, assigned to the Brunhes Chron. 

Zazhigin did not question Markova's identifications; 

had he done so he would have seen that what she called 

Microtus was what he called Allophaiomys (fig. 16). Using 

Markova's definitions of the genera, the Olyor fauna had 

primitive Microtus replaced by more advanced Microtus just 

below the beds with normal polarity, and there was no 

Allophaiomys at all in the Krestovka·Olyor, nor was there 

any Microtus as advanced as that from the Olyor in the 

Karay-Dubina fauna. 

If the Olyor fauna under discussion had been found 

north of the Black Sea (that is, in Markova's area of study), 

it would have been called "noticeably younger'' than the 

Karay-Dubipa fauna. But the Olyor fauna lived 125° farther 

east and 22° farther north than did the Karay-Dubina fauna; 

the living microtine faunas of the two areas are not at all the 

same today, and there is no reason to think that they were the 

same in the past. That a difference is reasonable and 

logical-and present-was not at all evident from the published faunal list of Sher and others (1979). 

The microtine rodents from the Olyor Suite of the Krestovka Sections have not been described or illustrated prior 

to the present report (figs.15, 16). The specimens illustrated 

by Markova as Allophaiomys (only three first lower molars) 

from Karay-Dubina, north of the Black Sea, appear to show 

a form similar to that named by Kormos from relatively 

nearby Romania. What Markova compared with a living 

species of Microtus ("Microtus ex gr. oeconomus," fig. 7, 

Nos. 23-32 of Markova, 1982; compare with figs. 11, 16, 

and 17 of the present report) is a form of Lasiopodomys now 

(but not in 1984) seen to be no more advanced than the specimens from the oldest faunas of the Olyor Suite, which had 

been listed as Allophaiomys (Sher and others, 1979). 

Incorrectly, the present author assumed (Repenning, 

1984) that a typical form, comparable to what Markova (fig. 

7, Nos. 12-14 of Markova, 1982) had called Allophaiomys, 

was what Zazhigin had listed as Allophaiomys in the compilation of the published Olyor faunal list. Further, he assumed 

that what had been called Microtus was an early form of 

Lasiopodomys similar to what Markova had referred to as 

Microtus ex gr. oeconomus. These assumptions seemed to be 

corroborated by other statements about the primitive nature 

of Microtus from the Olyor (Sher and others, 1979) and reference to its similarity to Microtus ratticepoides (Sher, 

1986), a species referred to Lasiopodomys by the present 

author. But neither assumption was correct. 

It now is obvious that what was called Allophaiomys 

from the Olyor Suite by Zazhigin is identical to what Markova called Microtus from the Karay-Dubina fauna (this 

report, fig. 16). Also, what. was called Microtus from the 

Olyor Suite by Zazhigin is what the author would also call 

Microtus and is more advanced than any form known from 

the Karay-Dubina fauna. Thus the replacement of Allophaiomys by Microtus, cited as evidence for the age of the Olyor 

Suite on the basis of the presumed age of the Karay-Dubina 

fauna, was a replacement of and by forms that differed in the 

definitions of Zazhigin and Markova. 

Typical Allophaiomys, like that called such by Markova, has been recognized in European deposits that date from 

the beginning of the Olduvai Normal-polarity Subchron 

(Zuurland Borehole; van Kolfschoten, 1988, 1990) and from 

deposits older than the Olduvai event in China (Zheng and 

Li, 1990). The genus is reported later in the present report 
6 AUOPHAIOMYS AND THE OLYOR. SUITE, YAKUTIA 

from near the base of the Olduvai in the United States (p. 31; 

fig. 7E). Records as old or older have been inferred elsewhere by faunal composition and geomagnetic polarity control external to the biochronology; these suggestively 

support an early age. Such records include the type locality, 

Puspokfurdo, Romania (faunal control); Villany-5, Hungary 

(faunal control); Kudun, western Transbaikalia (faunal control); Huangkan and CKT-18, China (People's Republic of 

China) (faunal and paleomagnetic control); and Java, South 

Dakota (faunal control) (fig. 1). Most of these published 

older records are reviewed in the present report. 

Species usually assigned to Microtus (most approximately the age of the Jaramillo event but a few nearly as old 

as the Olduvai event) and presumed to be older than the age 

reported by Markova (1982) include: Microtus "arvalides," 

M. "gregaloides," M. "ratticepoides," M. deceitensis, M. 

califomicus, primitive M. paroperarius, and ?M. oeconomus. Some, but not all, of these are referred to the genus 

Lasiopodomys in the present report. 

In addition, the age of the Karay-Dubina fauna of the 

Ukraine, described by Markova (1990), is not nearly as certain as suggested in most correlations; the fauna lies well 

below the oldest paleomagnetic control and well below the 

base of the Brunhes Chron (Velichko and others, 1983; 

Markova, 1982, 1990). In the present report it is considered 

older than the Jaramillo Subchron on faunal grounds. No 

paleomagnetic control of the section exists to indicate that 

the fauna is younger than, older than, or equal in age to the 

Jaramillo event. 

Allophaiomys was a temperate to subtropical rodent, 

and Microtus has arctic to temperate tolerances. Throughout 

the Northern Hemisphere evidence is abundant that the faunal replacement of Allophaiomys by Microtus was time 

transgressive: both genera moved southward with climatic 

deterioration throughout the hemisphere. The reverse was 

also true: Allophaiomys moved northward during periods of 

warming temperatures. (See Repenning, 1990; and Repenning and Brouwers, 1992.) In the most southerly regions 

(North Africa, Israel, Kashmir, southern China, and most of 

the United States), Microtus of Asian origin first appeared 

during the Brunhes Normal-polarity Chron, ne~ly 1 million 

years after its oldest record in areas farther north. These conditions influenced Repenning's (1984) interpretation of the 

age of the Olyor Suite, and led to his earlier, erroneous age 

interpretation. 

The oldest records of Microtus (usage of both Zazhigin 

and the present author, and as herein defined) are about 1.4 

million years old. However, this great age seems inconsistent with other records, and there is reason to be concerned 

about the independent origin of the genus at different times 

in different regions, as is discussed under the major heading 

"Provinciality" beginning on page 74. Before the recognition of reasons for inferring multiple origins of the genus 

Microtus, in the strict sense here used, Repenning (1984) 

reasoned that if primitive Microtus evolved in the Arctic 

Ocean Borderland (a possibility now considered uncertain), 

then the oldest primitive Microtus could be as old as or older 

than the Olduvai Normal-polarity Subchron in the Arctic. 

The climatic trends reported from the Olyor Suite seemed to 

indicate that the Olyor had to be somewhat older than 2.0 

million years. This conclusion now appears wrong and 

overly simplified. 

In an effort to resolve the differences of opinion regarding the age of the Olyor Suite of the Krestovka Sections, 

A. V. Sher invited the author to visit Moscow and to review 

the microtine fauna from this formation in 1990. Once 

examination of the oldest microtine fauna of the Krestovka 

Olyor Suite began in V.S. Zazhigin's office, it was obvious 

that the author's interpretation of the age of the fauna was in 

error. Great differences also became evident in the use of 

taxonomic nomenclature between Zazhigin, who had identified the Olyor microtine fauna, and the present author, who 

interpreted the age of the fauna from Zazhigin's faunal list. 

Nothing in the Olyor fauna belongs to the genus Allophaiomys as defined by Kormos (1932), as illustrated by 

Markova (1982), or as here defined. Instead, the author 

assigns to Lasiopodomys (primitive Microtus of many 

authors including Markov a, 1982) all of the micro tines in the 

fauna that Zazhigin assigned to Allophaiomys. Although 

Zazhigin was recognizing Allophaiomys as a genus distinct 

from Microtus, his morphologic concept of Allophaiomys 

was similar to that of Chaline (1972) in that it included morphotypes totally unknown in the type population. The 

present author includes these in Lasiopodomys; Markova 

(1982, 1990) included them in Microtus, which has been a 

common procedure. 

When the present author (Repenning, 1984) inferred 

the age of the Olyor Suite from the faunal lists given by Sher 

and others (1979), he was mistaken about the nature of the 

fauna. When Sher and others (1979) and Sher (1986) 

inferred the age of the Olyor Suite from faunal lists given in 

Markova (1982) for the Karay-Dubina fauna, they were mistaken about the nature of that fauna. What was listed as Allophaiomys from the Olyor fauna has no similarity to what was 

listed as Allophaiomys in the Karay-Dubina fauna; instead it 

is identical to what was listed as Microtus in the KarayDubina fauna (fig. 16). Without uniform taxonomic definitions it is impossible to correlate from faunal lists. 

As Allophaiomys is recognized in the present report, by 

Markova in 1982, and by Kormos in 1932, no record of the 

genus exists either in the Olyor Suite of the Krestovka Sections or in the rest of Beringia. The time of its dispersal to 

North America, just before the beginning of the Olduvai 

event, is not recorded in Beringian fossil records. That 

Allophaiomys passed through Beringia enroute to North 

America is obvious from the fossil record in the United 

States, but its date of passage must be inferred from the age 

of its earliest North American record. 

As well as lacking a record of Allophaiomys, Beringian 

fossil faunas also lack a record of tribe Pitymyini. The tribe 

Pitymyini (Repenning, 1983) is the other major group 

derived from Allophaiomys, in addition to tribe Microtini 
CONVENTIONS 7 

including Microtus and Lasiopodomys. Like Allophaiomys 

(but unlike the Microtini), the Pitymyini are temperateclimate rodents and are not found in the Arctic region. However, the pitymyinine genus Terricola (replacing the Nc;>rth 

American name Pitymys in Eurasian faunas, following Chaline and others, 1988), also dispersed to North America but 

has no record in Beringia. The Pitymyini will also be discussed in this report, but in less detail than those lineages 

present in the Olyor Suite. 

The present author takes the lack of any fossil record of 

Allophaiomys or Terricola in Beringia as a suggestion of the 

lack of any Beringian records of the times of their dispersals, 

which were about 1,900,000 and 850,000 years ago, at the 

beginning of the Olduvai event and between the time of the 

Jaramillo event and that of the Brunhes Chron. For 1 million 

years after the beginning of the Olduvai event, Allophaiomys 

was common in the United States east of the Rocky Mountains. After 850,000 years ago Terricola is kn~wn from 

many faunas in the United States west of the Mississippi 

River and from Mexico (Repenning, 1983). 

The time of the dispersal of Allophaiomys through Beringia immediately followed the frrst major continental glaciation of North America, and the dispersal of Terricola 

immediately preceded the second. As has been stated, Beringia was not glaciated, but continental ice elsewhere in the 

Northern Hemisphere, and the resulting lowered sea level, 

seem to have been unfavorable conditions for preserving 

deposition in Beringia. The same phenomenon has been 

observed in lower latitudes such as the East Coast of the 

United States, where deposits during glacial periods are rare 

(T.A. Ager, written commun., 1992). 

V.S. Zazhigin, A.V. Sher, and the author have agreed 

(1990) that differences in the definitions of the genus Allophaiomys and of those genera derived from Allophaiomys 

are a major handicap to global correlations of terrestrial 

deposits of late Pliocene and early Pleistocene age. This 

handicap is nowhere more obvious than in interpreting the 

biostratigraphy of Eurasian and North American Beringia, 

where differing taxonomic definitions resulted in a difference of about 1 million years in age interpretation within a 

biostratigraphy potentially capable of 5,000-year age discrimination (fig. 2). 

Allophaiomys was once present throughout the Northem Hemisphere, from the Arctic Ocean (briefly) to the Mediterranean and Black Seas and to the Gulf of Mexico. Its 

definition, distribution patterns, and history are of significance over a much greater area than the Arctic Ocean 

Borderland. The same distribution and significance were 

later assumed by the complex genera Microtus, Pitymys, and 

Terricola. Review and definition of the microtine genus 

Allophaiomys, and its derivatives Lasiopodomys, Microtus, 

Pitymys, and Terricola, are thus important to intercontinental correlation throughout the Northern Hemisphere. Allophaiomys is not present in the faunas of the Olyor S~ite, and 

this puts an entirely different constraint on the interpretation 

of the age. What is present, that was called Allophaiomys, 

adds a different constraint to the interpretation. 

By analysis of North American microtine history, a biochronology for the eastern two-thirds of the United States 

from 2 million years ago until today is here produced. 

Although still imperfectly known over some periods of time, 

this biochronology is reasonably discriminate to the unprecedented precision of between 5,000 and 10,000 years during 

other periods. This precision is made possible only by 

observing a uniform taxonomy, by estimating stage of evolution through consideration of the population structure in 

fossil samples, and by inferring dispersal patterns. 

The known microtine biochronology, in combination 

with a cold peak in the climatic record of the Arctic Ocean 

and its borderland, indicates that the oldest normal polarity 

in the Olyor Suite of the Krestovka Sections must represent 

the Cobb Mountain Normal-polarity Subchron, as is also discussed (fig. 14). If present in the Krestovka Sections, the 

Jaramillo Subzone of the Matuyama Zone must be unconformably·overlain by the Brunhes Zone, either in the youngest part of the Olyor Suite or in overlying stratigraphic units. 

. The microtine faunal samples known from these units are too 

small in specimen numbers to be definitive (A.V. Sher, oral 

commun. 1990). 

The Cobb Mountain event was defined by Mankinen 

and others (1978) from a record in central California, U.S.A., 

and is one of the best dated of the short polarity reversals of 

the Brunhes and late Matuyama Chrons; it is 1.10 million 

years old. Although of short duration (possibly only 10,000 

years) the event has been widely recognized (Mankinen and 

Gromme, 1982). The present report is the first to recognize 

the Cobb Mountain event by means of microtine biochronology, in association with a climatic extreme in Y akutia and, 

by rate of sedimentation and the same climatic correlation, in 

CESAR core 14 on the east end of the Alpha Cordillera, 

Arctic Ocean. 

What has emerged from this investigation of the differences of opinion about the age of the Olyor Suite in 

Y akutia is an understanding of the evolution of many 

microtine rodents, and of their distribution patterns 

throughout the Northern Hemisphere. This understanding is 

so complex that serious questions arise about the current 

concepts and applications of biochronology, evolution, and 

classification. The complexity seems overpowering, but is 

not more complex than late Pliocene and early Pleistocene 

climate change in the Northern Hemisphere, to which it is 

closely tied. Understanding is a prerequisite for compiling 

the terrestrial record of this climate change (for example, 

Repenning and Brouwers, 1992). 

CONVENTIONS 

In this discussion the cricetid rodents with alternating, 

hypsodont, triangularly prismatic cusps on their cheek teeth 

are called "microtine rodents." The term as here used is vernacular and has reference neither to systematic nomenclature 
8 ALLOPHAIOMYS AND THE OL YOR SUITE, Y AKUTIA 

Time Sher and others, 1979 Repenning, 1984 This report Climate lnMa Sher, 1986, 1987 

I 

0.5 Glaciation 

~ Suite 0/yor IE[I 0/yor IJil 1 Suite 

a 0/yor FOREST 

1.0 

Suite TUNDRA 

c( 

ALTERNATING :& 

c( 1.5 FOREST AND TUN 

> 

::;) 

1-

c( 

:& FOREST 

2.0 B 0/yor 

Suite T 

Glaciation 

Kutuyakh 

• 

TUNDRA 

2.5 • Kutuyakh 1 • Kutuyakh Beds 

Beds Beds PERMAFROST 

• Begunov • Begunov FOREST-TUNDRA 

Suite Suite FOREST 

Figure 2. Different age assignments of formations in the Krestovka Sections, and associated geopolarity and climate evidence. 

nor to taxonomic rank. It is synonymous with "arvicolid" 

and "arvicoline" as widely used, especially in Europe, 

although these two terms are also still used with reference to 

formal nomenclature: to the herein-abandoned family Arvicolidae and to the subfamily Arvicolinae. There remains, in 

the classification here followed (Repenning and others, 

1990), a tribe Microtini, vernacular reference to which is 

spelled "microtinine" and a tribe Arvicolini, informally 

called "arvicolinine." 

VERNACULAR NOMENCLATURE 

In 1896 G.S. Miller abandoned the genusArvicola and, 

somewhat improperly by modem rules, also Gray's (1821) 

family Arvicolidae that was based upon this genus. Miller 

substituted Cope's (1891) term Microtidae. It was a frail and 

somewhat questionable procedure that he made even more 

questionable in 1912 by reinstating the genus Arvicola, but 

neglecting to return to Gray's familial term, which he had 

rejected 16 years before. 

Nevertheless, from 1896 until 1962 the group of hypsodont cricetid rodents herein called "microtines" were 

included in the family Microtidae of Cope and the members 

of this family were universally referred to as the "microtine 

rodents" in vernacular usage and in reference to the family 

Microtidae. But in 1962 M. Kretzoi reminded the world that 

the family name Arvicolidae of Gray (1821) had priority (it 

did not, according to Section VI, Art. 23b, of the International Code of Zoological Nomenclature under which rule it 

was a nomen oblitum), and Kretzoi's observation was noted 

by Repenning ( 1968). After that time the group was referred 

to as the family Arvicolidae, vernacular "arvicolid," until it 

was generally recognized that the family had multiple origins out of other members of the family Cricetidae with lowcrowned cheek teeth. The family Arvicolidae was thus seen 

as an evolutionary grade of cricetid specialization, rather 

than an evolutionary lineage, and did not merit familial 
CONVENTIONS 9 

recognition. Thus the recognition of either family Arvicolidae or family Microtidae became a subject of conceptual 

discussion, rather than of nomenclatorial ordinance. 

Most workers now recognize several subfamilies of 

"microtines" in the family Cricetidae, the subfamily Arvicolinae being restricted to the clade containing the genus 

Arvicola, and a separate family, Arvicolidae or Microtidae, 

is not recognized. The classification here followed (Repenning and others, 1990) recognizes five microtine cricetid 

subfamilies: Lemminae, Prometheomyinae, Arvicolinae, 

Ondatrinae, and Dicrostonychinae. The subfamily Arvicolinae contains several tribes, one of which is the tribe Microtim, members of which this report addresses. 

Although no longer considered as representing a unique 

family, these hypsodont cricetid rodents, comprising several 

cricetid subfamilies, still need a vernacular term by which to 

refer to them; and the present author uses the term "microtine," as have many (but not most) in the United States. The 

vernacular term "microtine" was universally used prior to 

Kretzoi's synonymy of 1962, and the author's preference, 

followed in this report, probably reflects his great antiquity. 

European workers, on the other hand, are more impressed by 

the synonymy of Kretzoi in formal classification and, 

although the familial status of the group, and Kretzoi's synonymy, have no bearing on the vernacular name (as the 

familial Arvicolidae is not used), they use "arvicoline" or the 

familial termination "arvicolid" as a vernacular term. This is 

acceptable; there are no rules governing the use of vernacular terms. 

"Microtine," "arvicoline," and "arvicolid" are all informal terms for the same thing; they refer to the hypsodont 

cricetid rodents formerly included in the family Arvicolidae, 

or the family Microtidae between 1896 and 1962. The preference now is largely a matter of where one is born, and the 

author of this report prefers "microtine" out of habit prior to 

1965, when he became aware of Kretzoi' s synonymy. 

"Arvicoline" and "arvicolid" are just as . appropriate, 

although the family is no longer recognized, but many 

microtines do not belong to the subfamily Arvicolini. All 

microtines are cricetid rodents, not arvicolid rodents; some 

microtines are arvicoline rodents. 

The present report develops a history of the genus Allophaiomys (tribe Arvicolini of the subfamily Arvicolinae) and 

those genera that evolved from it (forming several other 

tribes of the same subfamily); all are microtine rodents and 

also all are arvicoline cricetid rodents, but not all microtines 

are arvicoline rodents, such as lemmings and muskrats. 

TIME SCALES 

History cannot be developed without some temporal 

control for the occurrence of events. There is an increasing 

awareness that the only truly synchronous global time 

markers currently available in the study of Earth history are 

the global magnetic polarity reversals .. Even these have an 

element of imprecision, in that these reversals are not 

instantaneous but occur over a short period of time and even 

incorporate periods of no polarity. However, in comparison 

with all other methods of estimating historical synchroneity 

on a global scale, geomagnetic polarity reversals may be 

considered as instantaneous time markers. A second criterion for synchroneity is global climate change, although this 

is more difficult to recognize and correlate. 

The weakness of using polarity reversals is the inability 

to tell one reversal from another; at a polarity boundary the 

Earth's polarity changes from normal to reversed, or the 

other way, and so appears identical, paleomagnetically, to 

half of the other polarity boundaries that have ever taken 

place. At present, the only way to identify a particular polarity reversal is to have some rather close measure of its geologic age, a measure accurate enough to eliminate ambiguity, 

or to have a complete record from the present so that one can 

count back in time to identify the polarity reversal of concern, such as is done in oceanic cores. The last procedure 

assumes that the record examined does not contain any 

previously unidentified polarity reversals or any missing 

reversals because of depositional hiatus; associated biochronologic ~ontrols usually can help identify such irregularities. 

Because of the global synchroneity of geomagnetic 

polarity rev4~rsals, greater efforts are being made to incorporate these reversals in the designated type stratigraphic sections that contain the benchmarks for the definitions of 

geologic time units. Present tradition seeks to avoid ambiguity by requiring that these benchmarks be placed at physical, 

visible changes in lithology. These changes usually do not 

quite coincide with invisible polarity reversals, thus introducing ambiguity into the correlation between the strongest 

evidence of synchroneity and the definition of a presumably 

synchronous geologic time boundary. 

Possibly we are approaching a time when tradition will 

be abandoned in favor of accuracy and rationality. Possibly 

it will be seen that units of time should be defined on the 

evidence of time. Since the concept of time-transgressive 

rock units became accepted, the world has recognized that 

mappable, visible rock units do not coincide with invisible 

time units. There is no such thing as a "time-rock unit"; 

either the time represented in the concept is not a temporal 

unit or the rock represented is not a lithologic unit. 

But custom still demands that we define time units on 

the basis of what can be seen in rock units at a type section. 

The demand is a holdover from earlier periods when geologic time could only be guessed, and stratigraphic succession was the only evidence of greater or lesser age. But, as 

the demand persists, an explanation of geologic time terms 

mentioned must be made. Note that as much as possible, 

these terms, are avoided in this report, and age is indicated in 

radiometric: years. 

The early-middle Pleistocene boundary is here 

placed at the beginning of the Brunhes Normal-polarity 

Chron (about 0.79 Ma; lzett and Obradovich, 1991). This 
10 AUOPHAIOMYS AND THE OLYOR SUITE, Y AKUTIA 

is an approximation until international agreement is 

reached-a type section for the stratigraphic authentication 

of this time boundary has not been selected. 

The Pliocene-Pleistocene boundary is placed just after 

the end of the Olduvai Normal-polarity Subchron of the 

Matuyama Reversed-polarity Chron (about 1.67 Ma)-the 

type section has been selected at Vrica, Italy (Aguirre and 

Pasini, 1985). 

Arbitrarily, the Gauss-Matuyama polarity boundary 

(2.48 Ma) is approximately used as the boundary between 

middle and late Pliocene. However, a global microtine dispersal event took place shortly before this polarity reversal 

(2.6 Ma in Repenning, 1987, and revised to 2.56 Ma in the 

present report on the basis of the first increase in activity of 

the Scandinavian Ice Sheet; Jansen and others, 1988). The 

middle-late Pliocene boundary is usually considered to be at 

this dispersal event in discussing microtine ages. This usage 

is one of convenience in the lack of a formal definition; it is 

not a statement that a biologic event is any more reliable as 

a time horizon than is a sedimentation event. 

Microtine age terminology used herein for the Pliocene 

and Pleistocene in the United States is that of Repenning 

(1987), with the exception that Irvingtonian III replaces Rancholabrean I, and Rancholabrean II is herein referred to as 

undivided Rancholabrean. Microtine age terminology for 

Eurasia follows that used by Repenning, Fejfar, and Heinrich 

(1990), with revisions where now recognized. 

DENTAL MORPHOLOGY 

The terminology of the parts of micro tine teeth (fig. 1 0) 

follows that of Repenning (1983); dimensions follow the 

scheme of van der Meulen (1973 and later publications) 

with one significant addition here called Dimension A-A'. 

Specifically defined morphologic terms of the first lower 

molar (Mil) are capitalized to call attention to their specified meaning; these include numbered Triangles, Anteroconid Complex (protoconid complex in the [former] 

U.S.S.R.), Primary Wings, Secondary Wings, Cap, and 

Dimensions A-A', B-B', and C-C'. Dimension D-D' of van 

der Meulen (1978), the width of the Cap when no Secondary 

Wings are present, is mentioned but not used. In 1973 van 

der Meulen used dimension "d-d'" (in his fig. 22) in the 

sense that Dimension A-A' is used herein, which is not 

quite the same as his 1978 use ofD-D'. 

In nearly all publications, the assignment of last upper 

molars (M\3) to species, which have been identified on the 

basis of the morphology of the first lower molar (M/1 ), is not 

done on a statistical basis, and the taxonomic assignments 

reflect entirely the preconceptions of the author. Nevertheless, in some circumstances it is not possible to identify a 

microtine species without consideration of the nature of its 

last upper molar. 

Herein, when the faunal sample size merits it, assignment of the last upper molars to the species recognized by 

their frrst lower molars is made on the basis of the proportions of first lower molars in the sample. If a determined percentage of frrst lower molars in the sample belong to one 

species, it is assumed that the same approximate percentage 

of the sample applies to the last upper molars. This assignment is, of course, made within the context of the known last 

upper molar morphologies that have been associated with a 

particular first lower molar morphology in the history of the 

lineage. Direct associations are rare; there are very few fossil specimens in which the first lower and last upper molars 

of an individual microtine rodent are physically associated, 

and the association is usually made from a faunal sample of 

isolated teeth. 

In describing the microtine rodents of the Cumberland 

Cave fauna, Maryland, van der Meulen (1978) distinguished 

three types of last upper molars: A, B, and C. He included in 

his Morphotype C the complex morphotype (with a posterior 

hook; this report, fig. 1 0) that is associated with typical 

Microtus paroperarius and many living species. His figure 

illustrating the types of M\3 (van der Meulen, 1978, fig. 6) 

did not show great development of Morphotype C and it is 

more typically illustrated in his figure 11H and I. Other M\3 

morphotypes could be defined, but the rarity of associated 

first lower and last upper molars in fossil faunas seems to 

obscure the value of such precision. In the present report van 

der Meulen's M\3 Morphotypes A and B are referred to as 

"simple" and his Morphotype C is called "complex." 

VanderMeulen's (1978) M\3 Morphotype B is one in 

which the two central triangles are very confluent (this 

report, figs. 3L and 13K), and he reported Morphotype Bin 

his species Pitymys cumberlandensis, a North American lineage. Here, Morphotype B is included in the "simple" pattern. Individual examples of Morphotype B are present in 

many populations of Allophaiomys, as well as in other 

genera. 

Chaline (1974) considered this M\3 pattern (van der 

Meulen's Morphotype B) to be characteristic of Allophaiomys laguroides from Betfia-2, a species that he had earlier 

(Chaline, 1972) considered synonymous with A. pliocaenicus. In 1974 he stated that this form ofM\3led directly from 

Microtus (Allophaiomys) pliocaenicus laguroides (his 

nomenclature) to his subgenus Microtus (Meridiopitymys). 

In contrast, Ognev (Vol. VI, 1948) thought that what 

Chaline (1972) later called subgenus Meridiopitymys should 

be placed in Microtus (Micrurus) of Forsyth-Major (1877), 

if separated from North American Pitymys. But in his Volume. VII (1950) Ognev recognized no morphologic reason 

for such separation of Eurasian forms from North American 

Pitymys and did not use Micrurus, but continued the usage of 

Pitymys for Eurasian forms. 

In the present report Old World "Pitymys" is removed 

from that North American genus and placed in Terricola, 

as was done by Chaline and others (1988). Micrurus 
CONVENTIONS 11 

Forsyth-Major is recognized as the junior homonym of 

Micrurus Wagler (1824), a coral snake; and Meridiopitymys Chaline (1974) is considered a junior synonym of Terricola because van der Meulen's last upper molar 

Morphotype B does not seem to be restricted to a single 

lineage. 

Although van der Meulen (1978) has stated that his M\3 

morphotypes also differ in their enamel-thickness differentiation, it has not been obvious in the present study that the 

morphotypes can be correlated with enamel-thickness patterns except in a most general way. 

"Simple" M\3s are associated with all populations of 

Allophaiomys, and usually have "intermediate" enamelthickness differentiation (no difference in enamel wall thickness); primitive populations have a high percentage of 

"Mimomys" enamel-thickness differentiation (enamel is 

thicker on the posterior walls of the prisms of the lower 

teeth). "Complex" M\3s appear to be associated with Allophaiomys only in those populations where individual variation in the M/1 morphology strongly overlaps the characters 

of some derived genera, and these overlapping variants 

sometimes have "Microtus" enamel-thickness differentiation (anterior walls of the alternating triangles on the lower 

teeth have thicker enamel). Although somewhat variable in 

the living genera Pitymys and Pedomys, all other living 

genera derived from Allophaiomys have "Microtus" differentiation apparently with only one exception: Microtus xanthognathus from the Canadian taiga, which varies from an 

"intermediate" to very weak "Microtus" enamel-thickness 

differentiation. Martin (1987) noted that "Microtus" enamelthickness differentiation is also not present in the Central 

American species Microtus oaxacensis, Herpetomys guatemalensis, and Orithriomys umbrosus. These last three species have not been reviewed from a satisfactorily large 

sample in this study, and are not discussed. 

The most primitive populations of Allophaiomys have 

some individuals with "Mimomys" enamel-thickness differentiation, but this is also occasionally found in later populations and in Lasiopodomys (fig. 16A). Lasiopodomys, 

Pitymys, Pedomys, and some species of living Microtus and 

Terricola (using genera as defined in the appropriate sections that follow) retain a "simple" M\3, but the living forms 

usually have "Microtus" enamel differentiation. Enamelthickness differentiation follows a broad trend from the 

"Mimomys" type to the "Microtus" type, which is also seen 

in the evolution of Arvicola (von Koenigswald, 1973), but it 

appears to proceed in a rather inexact way and cannot be correlated with other characters. 

Efforts have been made to reproduce enamel thickness 

faithfully in the illustrations of this report. The enamelthickness pattern is uniform in all cheek teeth of the individual, but the pattern is reversed between the upper and lower 

teeth. 

The posterior loop and the three basic triangles (fig. 1 0) 

are features on the first lower molars of all microtine rodents 

(except the Ondatrinae and Dicrostonychinae, which have 

more basic triangles), and are not discussed. The posterior 

loop of the frrst lower molar extends lingually in all microtine rodents; thus the first basic triangle (most posterior; T .1) 

is on the lingual side (fig. 10). Except for Proedromys, the 

posterior salient angle of the last upper molar extends lingually in all microtine rodents. 

Salient angles are the lateral points of triangles, wings, 

and hooks, on both sides of the tooth; they are not specifically defined here but are conventionally numbered from the 

rear of the lower tooth forward in buccal and in lingual 

sequences, including the buccal and lingual angles of the 

posterior loop. The abbreviations LSA and BSA (lingual 

and buccal salient angles) are often used in describing microtine teeth, but are not used herein. 

Reentrants (sometimes called synclines) are the valleys 

between the triangles, on either side of the tooth, in which 

the enamel walls of the triangles turn toward the midline; in 

the microtines here discussed they are filled with cementum 

(stippled on the illustrations). Reentrants are usually numbered in the same manner as are salient angles, in buccal and 

lingual series (fig. 1 0). The abbreviations LRA and BRA 

(lingual and buccal reentrant angles) are often used in 

describing microtine teeth (and are illustrated in fig. 10), but 

are seldom used in the descriptions of the present text. 

In contrast to the numbering of the salient angles and 

the reentrant angles, triangles are numbered anteriorly in one 

sequence and exclude the posterior loop. The sequence disregards which side of the tooth is represented, but, as the triangles alternate, the even numbers are buccal. Thus "lingual 

salient angle 2" would be on Triangle 1, or "lingual salient 

angle 4" would be on Triangle 5 (or. the lingual Primary 

Wing if it has not formed a triangle; fig. 10). The abbreviation "T" is often used for triangles in describing microtine 

teeth, but is used only occasionally herein. 

In all figures anterior is shown upward. Scale is shown 

on each figure. In all figures, as many specimens as feasible 

have been shown to illustrate variability. The ownership of 

specimens illustrated is indicated by the acronyms given in 

the "Acknowledgments" section (p. 4). Specimens not credited to these acronyms are in the author's collection in the 

U.S. Geological Survey, Denver, Colorado. 

"Typical" is used here in a double context, referring to 

either the type specimen or the type population. Where used 

to describe an individual it refers to the morphology of the 

type specimen. Where used to describe a sample of a population it refers to the range of morphologic variations 

included in the type population; this range includes some 

concept of the proportions of various morphotypes within 

the type population. The definition of a type species with 

great variability should, therefore, include the "typical" morphology (and the type specimen should be within this group), 

the approximate percentage of this variant in the total sample 

of the population, and some indication of the morphologic 

extremes of the type sample. The concepts of both the 
12 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

morphology of the type specimen and the limiting range of 

variation recognized in the type population are included in 

the word "typical," but the application of these descriptions 

varies depending upon whether an individual or the entire 

known sample is being discussed. 

Both morphology and variability are needed to judge 

stage of evolution and identity of the taxon represented by a 

population sample. Populations that contain some individuals with a morphotype similar to the most common ("typical") morphology of the type population may have a 

different range of variation than the type population; such 

are not considered "typical" populations, although they may 

contain "typical" individuals. Individual variants within any 

population may be called "typical" morphotypes if they are 

similar to the type specimen, but, if the population variability 

differs to any significant extent from that of the type population, the name given to the type population should not be 

used. As might be expected, few fossil populations are "typical" (with the morphologic range varying as does the type 

population), but most populations contain some individuals 

that are morphologically "typical" individuals. The word 

"typical" is placed in quotation marks where it is thought that 

its meaning, as defined here, might be misunderstood. 

VARIABILITY AND EVOLUTION 

G.G. Simpson (1945, p. 14) said: "The thing that is 

actually classified is an inference, a purely subjective concept, which approximates a real, but unobservable, morphologic unit, which in tum approximates an equally real but 

even less observable genetic unit." This purely subjective 

concept is seldom discussed but is in the mind of anyone 

required to identify a specimen; it is the identifier's opinion 

of the amount of variability that can be tolerated within the 

named taxon to which the specimen might belong. The type 

specimen of the named taxon is presumed, often incorrectly, 

to show the midpoint of whatever variability can be tolerated. The concept of the range of tolerable variability is often 

formed by comparison with a similar living taxon whose 

range of variability has been established by sampling. But 

the purely subjective nature of this concept of tolerable variation is what permits the separation of the "splitters" from 

the "Jumpers." 

Now, nearly half a century after Simpson's statement, 

greater efforts and improved techniques provide a much 

more detailed view of the "unobservable" morphologic unit, 

particularly for micromammals. This improved view, resulting from the study of population samples, eliminates the 

need to make inferences based upon similar living taxa. In 

samples of significant size the range of individual variability 

of the population is directly observable. While the type specimen remains the name bearer, the morphologic variability 

of the species is defined by the type population, by direct 

observation of a statistically useful sample of the 

morphologic unit. This range of variation is genetically 

controlled and taxonomically significant, and it should be 

included in diagnosis. 

Frequently, fossil species are found to have greater 

morphologic variability than living populations of a similar 

taxon. Although this condition raises doubt about the singletaxon nature of the population and encourages enthusiasts to 

invent more names than there are taxa, this difference in the 

range of variability reflects evolution; it may reflect evolution through the time of fossil accumulation by "time averaging," which will vary with collecting techniques as well as 

depositional rates. To the extent that the sample represents 

a single population, variability is taxonomically significant, 

a significance that is hidden by the application of several 

names to variants of a single population, of a single taxon. 

Since C.R. Darwin first made the discussion popular, 

the process of evolution has been almost constantly debated. 

But to understand evolution there is no need to psychoanalyze the statements of everyone who has voiced an opinion; 

the process is logical, and only logic is needed to understand 

it. The elementary point of logic is that the history of evolution is reconstructed by consideration of known facts and by 

suggesting hypotheses that seem to describe and explain 

these facts, not by creating a hypothesis and then manipulating facts to fit. 

To his detriment, the present author is not versed in the 

many hypotheses expressed in the literature. To his surprise, 

he finds that not all of those engaged in the study of the facts 

of evolution, and their significance in classification, have 

thought out the logic of the fossil record of evolution. Should 

the reader wish more details of the thoughts of others regarding the process of evolution (and resulting classifications) 

than are discussed herein, the author recommends the more 

explicit publication of P.D. Gingerich (1979) called, "The 

stratophenetic approach to phylogeny reconstruction in vertebrate paleontology." 

The author has one objection to Gingerich's paper, and 

that is to his term, "stratophenetic," for a completely logical 

and conventional approach to the interpretation of the fossil 

evidence of evolution. The term denotes stratigraphic superposition as evidence of chronologie sequence, which is the 

least questionable of several methods that Gingerich has 

used to establish chronologie sequence, as he noted (1979, p. 

54). However, the term would better be "chronophenetic," 

because time sequencing of morphologic change is what 

Gingerich achieved by determination of stratigraphic superposition, and he also established and defended this time 

sequencing by other means, in addition to superposition. 

Without temporal sequencing of data, the discovery of 

evolutionary history (or any history) is a matter of chance; 

and the historical interpretation relies entirely on the preconceptions of the interpreter. Additional means are now available to establish time sequence, means that were not 

functionally usable in the late' 1970's, when Gingerich composed his explanation of the evolutionary interpretation of 
VARIABILITY AND EVOLUTION 13 

the fossil record. And others are available in the Pliocene and 

Pleistocene (of concern to the present report) that are not yet 

available in the early Tertiary of the Bighorn Basin of Wyoming, the source of Gingerich's illustrations. 

The fossil record of the microtine rodents is notable in 

its minimal control by stratigraphic superposition, although 

when available such evidence is considered irrefutable. 

Temporal sequencing is established more often by (1) paleomagnetic stratigraphy, (2) stratigraphically sequenced 

(with the fossils of concern) radiometrically dated rocks or 

chemically identifiable tephra that have been so dated in 

other regions, (3) correlation with other known microtine 

biochronologies, (4) known (and dated) dispersal data, (5) 

climatic events recognizable as those that have been dated 

elsewhere, (6) occasionally by association with other fossil 

types having significant biochronologic constraints, and (7) 

occasionally by dated tectonic events. These all, in addition 

to stratigraphic superposition, provide "chronophenetic" 

information. But all require careful evaluation of the evidence, an evaluation usually and obviously unnecessary with 

the evidence of stratigraphic superposition. 

The testimony of the present report, of Gingerich 

(1979), of Bown and Rose (1987), and of other authors is 

that populations evolve through progressive changes in the 

range of their individual variability. This testimony has been 

stated earlier by others in other situations (Walliser, 1964; 

Murphy, Matti, and Walliser, 1981; and Woodburn, 1987). 

Shaw (1969) observed the phenomenon in the fossil record 

of conodonts and suggested that it caused such confusion 

that the use of binomial nomenclature should be abandoned 

in paleontology and replaced by character-complex codes. 

However, not all possible solutions to the problem were considered, nor were all implications. 

As pointed out by Fejfar and Horacek (1983), typical 

Allophaiomys pliocaenicus has a few individuals in its population that overlap the morphology of Terricola. (Except 

for Phaiomys morphotypes, the characters of no other 

derived genus are involved in the individual variability of the 

type population.) In younger, more advanced populations 

(sometimes a different named species), there is an increase 

in the percentage of individual variation in the direction of 

Terri cola, and a minor but significant proportion of individuals have this morphology. With continued development of 

this change in variation, more than half the population later 

attains a Terricola morphology; it is at this point that the 

population must be assigned to Terricola-no longer can it 

be called Allophaiomys. Finally, the population of Terricola 

polarizes or stabilizes its morphologic variability so that few 

or no individuals remain with an Allophaiomys morphology, 

and then it can be called "typical" Terricola. The present 

report contains many examples. 

Such evolution through shifting individual variability 

in morphotype modes obviously occurs, with time, within a 

population. At least within the microtine rodents, it does not 

occur in all populations around the world at the same time 

nor with the same vector. Multiple origins of the microtine 

tribes and genera here recognized are documented in the 

following discussion. (See fig. 14.) As much as possible, 

species are used to represent groups of a single origin, but 

much work remains to be done to confirm this in many 

examples. (Note, again, that in illustrations of this report, as 

many specimens as reasonable have been figured to illustrate 

population variability.) 

Species are not fixed, sharply diagnosable morphologic 

units, as we have tried to think of them since January 1, 17 58 

(the arbitrary date of Linnaeus' tenth edition of Systema 

Naturae); they are stages in the continuum of evolutionary 

change, having broadly definable morphologies that characterize that stage, but are sharply definable only by their 

specific range of variability within a population. 

The definition of a species varies with the temporal 

constraints of a population. Species are much more easily 

defined in the instant of neozoology than in the time-depth 

of paleozoology, but one wonders how much change might 

be noticed if the details available today were available over 

the 235 years since 1758. Until a "paleontologic" view of 

"present" is available, there seems little hope that scientific 

emotion will be inclined to view species as other than the 

static forms envisioned by Linnaeus. 

Allophaiomys was the common ancestor of many taxa, 

as suggested by Kormos (1932), maintained by Kretzoi 

(1959), and demonstrated by Chaline (1966). Particularly in 

their earlier forms, all of these descendants show considerable variability in tooth pattern that overlaps the dental pattern of typical Allophaiomys; none show the typical range of 

morphologic variation, however. Today all lineages of greatest antiquity (most removed in time from Allophaiomys) 

include no individuals with a typical Allophaiomys morphotype. The most recently derived lineage, North American 

Pedomys, still contains some individuals with a typical Allophaiomys morphotype (R.A. Martin, written commun., 

1989). 

The entire process is gradational, and during most of the 

historical record of every lineage each population has some 

individuals that have the morphotype of its ancestral or of its 

descendant taxon, rather than of the modal morphology of 

the population, to which the population must be assigned. 

The range of morphologic variability in samples of living populations often, but not always, appears to be less than 

that observed in past populations. However, this is in part an 

illusion, as no lineage has stopped evolving just because it is 

now part of the living fauna. The modem situation is mostly 

an artifact of the circumstance that no descendant taxon of 

the future has yet been named; thus no defined future 

character states exist to be overlapped by existing genetic 

variance. 

Taxonomy is the practice of attaching names to stages 

within a continuum, but the practice tends to obscure that 

continuum by making it seem discontinuous. Our concepts 

of evolution are influenced by the taxonomy of others. 
14 AUOPHAJOMYS AND THE OLYOR SUITE, YAKUTIA 

The genetic-morphologic variability under discussion 

is that of defined taxa. Morphologic variability that does not 

overlap established taxon diagnoses is assumed to be random 

and of no evolutionary significance. Should the expanding 

record show that such a character has significance, then a 

new taxon needs diagnosis and naming, and the diagnosis 

should be based upon the character state that the record 

indicates is significant. "Before" and "after" character states 

must be recognized before the path of evolution can be 

documented. 

Only by outguessing evolution could a taxon of the 

future be named; to do so would be as pointless as tabulating 

random character states of unknown significance in the hope 

of discovering the path of evolution in the past. When a person first considers a specimen of a new taxon, that person's 

first statement is, "It looks kinda like so-and-so. But it 

doesn't have this and it has that." The first thought is of overlapping character states. The second is in diagnosis (Simpson, 1945, p. 22). From the moment of first consideration, 

classification is not based on random characters but on those 

of established significance, and their relative degree of significance is considered in detail. Only by outguessing evolution can the pattern of evolution be determined without 

consideration of the temporally sequenced fossil record. 

An interesting situation, not yet statistically defended, 

appears to be indicated in the living Pitymys pinetorum and 

may well be paralleled in other living species. Its apparent 

immediate ancestor, Pitymys cumberlandensis, seems 

clearly to have had less individual variability in its single 

diagnostic character (enamel-thickness differentiation) than 

does the living species. The ancestral species had primarily 

an intermediate enamel-thickness differentiation and 

remained stable in this character state for at least 135,000 

years. Yet the living species (P. pinetorum) appears to vary 

uncertainly but apparently quite widely between intermediate and "Microtus" enamel-thickness differentiation, possibly differing greatly in degree of variability between local 

populations, as will be discussed. The living species has 

increased its phenotypic variability in this character and 

may, in the future, polarize again into a stable character state 

with "Microtus" enamel-thickness differentiation, an evolutionary direction shown by all closely related lineages. 

The change in the range of individual variability within 

populations can be judged, or measured statistically, and 

compared with similar populations through time to evaluate 

relative stages of evolution. Such evaluations that are conformable to known age controls provide useful biochronologic information, as well as great detail of the record of 

evolution. 

Evaluation of phenotypic variance within populations 

exposes problems in the identification of taxa and demonstrates that such identification is dependent on population 

characteristics. In well-represented fossil samples of Allophaiomys (perhaps 25 or more first lower molars) containing 

morphotypes of one of its descendant genera, a complete 

gradation in dental patterns is often found between the morphotypes of the two diagnosed species. In such faunas, 

determining whether one or two species are present requires 

an abundance-of-morphotypes criterion: if the distribution 

is bimodal, two species are represented and some individuals 

between the modes cannot be certainly named. Bimodality, 

of course, is significant only if intergradation of morphotypes is continuous between the modes, thus identifying a 

single population. If not continuous, two populations and 

two taxa are present. 

Chaline (1966, 1972) was possibly the first to fully 

rationalize the taxonomic implication of this morphologic 

variability in the tooth patterns of the AllophaiomysMicrotus and Allophaiomys-Pitymys lineages; he was the 

first to thoroughly document it. This documentation was 

made by the description of fossil microtine faunas in France 

with intergrading morphotypes of these lineages. 

At first Chaline did not fully comprehend the significance of the great population variability and introduced a 

variety of new names. These can be seen, from his abundant 

illustrations, to represent individual morphotype variants 

within single populations. Thus in many cases single species 

with great morphologic variability were represented. The 

specific identity of the populations, to which he applied several names, can only be determined by a statistical evaluation 

of the entire sample and is not attempted herein, although in 

many cases Chaline provided enough illustrations of these 

variable, apparently single-species populations to suggest 

their identity. 

In a very real sense Chaline provided the evidence of 

evolution and then hid it behind the artificial definitions of 

his classification. In most of his examples, diagnosis of his 

taxa was impossible because only a single, intergrading population was represented. The study is a classic example of 

the difference between evolutionary gradation and systematic, diagnostic classification. One could diagnose most individuals of a single population as morphologically distinguishable species if one did not consider the probable 

structure of the (presumably) interbreeding population. 

Although the morphologic transition between fossil 

forms documented by Chaline clearly showed the anagenetic 

relationship between Allophaiomys and its descendants, it 

also created the impression of gene mixing-that the fossil 

and living genera (Allophaiomys, Terricola, and Microtus) 

all belonged in a single genus (for which Chaline selected 

Microtus). But morphologic intergradation does not indicate 

gene mixing, only genetic similarity; Allophaiomys has been 

extinct for 825,000 years, but some living derivatives still 

have individual variation that overlaps its dental morphology. In this discussion, morphologic intergradation is considered to indicate only temporal proximity to either linear 

(anagenetic) morphologic change or divergence toward a 

different taxonomic diagnosis. The condition could result 

from brief separation of subpopulations as well as from drift 

throughout the entire population; it is difficult to separate the 
VARIABILITY AND EVOLUTION 15 

causes, but in many cases it seems to occur with climatic 

change and the resulting morphologic change is coupled 

with change in environmental tolerance. Several examples 

are discussed herein. 

The morphologic intergradation that Chaline documented also seemed to show that all evolution out of Allophaiomys took place in France. However, the intergrading 

individual variability was the product of global conditions. 

Actually, France was on the fringe of some major evolutionary events and did not experience many of the major episodes in the evolution of lineages out of Allophaiomys that 

are known elsewhere. For example, in the nomenclature 

employed in the present report Lasiopodomys evolved from 

Allophaiomys and into Microtus; Markova (1982, 1990) 

described these forms from the Karay-Dubina and Shamin 

faunas north of Black Sea, van der Meulen (1973) described 

some from Italy, but in the French records of Chaline 

Lasiopodomys is missing, although the relationship between 

Allophaiomys and Microtus is evident in his faunas. Also in 

France, at least at the time of Chaline (1972), there appears 

to have been no fossil sample of Allophaiomys that had the 

minimal individual variability of the type population at 

Betfia-2, Romania. The individual variation in all of his 

samples is greater than that of the type population. Chaline 

recorded no microtine fauna that is comparable to that found 

in the older part of the Olyor Suite of Krestovka Sections, 

although these can be found elsewhere. 

Even with complete knowledge of population variability, species distinctions are vague during the speciation process, as is the definition of a fossil species as an 

isolated breeding unit. The Allophaiomys-Microtus and 

Allophaiomys-Pitymys lineages, identified only by their 

tooth morphology, apparently have been undergoing constant speciation for nearly 2 million years and in different 

places. During this time at least 10 genera (many more 

have been named), with very many species, have evolved 

from the single species Allophaiomys pliocaenicus. The 

evidence is abundant and worldwide. 

Kretzoi (1958) has indicated that more than 1,100 

micro tine species have been named, and the majority of them 

are the descendants of Allophaiomys pliocaenicus. The gradation of dental morphology between taxa has caused many 

to consider all as belonging to a single genus, the genus 

Microtus (following Chaline, 1966). 

Since Chaline's first defense of an all-inclusive genus 

Microtus in 1966, increasingly intensive study of fossil 

microtine rodents, in large part stimulated by Chaline's studies, has resulted in the discovery of many fossil faunas 

throughout the world that show aspects of the evolution of 

Allophaiomys. In 1966, for example, no one was aware that 

Allophaiomys had been an abundant part of the North American fauna for more than a million years. Chaline's interpretations and documentation were farsighted and enlightening 

a quarter of a century ago, but today interpretations must be 

made from the much larger record currently known, and 

from the sharply definable genera that eventually evolved. 

The micro tine rodents of the Allophaiomys-Microtus lineage 

from the Olyor Suite of the Krestovka Sections constitute 

one of these faunas that cannot be judged by 1966 standards. 

Since 1966, this overlapping morphologic variability 

has been considered as evidence of in situ evolution of Allophaiomys into more derived forms in many faunas. The origin of Microtus and (or) Pitymys (sensu lato) has thus been 

claimed from France to China, and in the United States 

because of such morphologic overlap. Most frequently both 

Allophaiomys and a derived genus have been reported from 

a single fauna. However, all such records are suspect until 

evidence is presented indicating that a single, morphologically intergrading population is not present. What has been 

lacking in previous interpretations is any consideration of 

population structure. 

In many cases where two taxa have been listed, consideration of the population structure indicates that only one 

taxon is present. In a few cases, the defining morphologic 

characters of the two taxa plot out bimodally and do not 

intergrade, and the original listing of two taxa is justifiable. 

It is emphasized that for taxonomic purposes the evaluation of overlapping variability applies to only those characters of taxonomic significance in diagnosis. Until it is 

established that the character to be evaluated is significant in 

the recognition of the stage of evolution within the lineage, 

evaluating its variation within the population has little value. 

Many variations in dental characters of microtine rodents 

occur throughout the group and have no taxonomic 

significance-for example, the strange irregularities on the 

triangles of 'Terricola meadensis from the Hansen Bluff 

fauna (fig. 13G). The occurrence of similar irregularities in 

individuals of other taxa should never be, and hardly ever 

has been, considered significant; they have never been found 

to conform to a pattern. 

Examples of population variability are discussed in the 

following consideration of the history of Allophaiomys and 

its living and extinct descendants. The evaluation of these 

morphologic modes is a statistical procedure and cannot be 

made with small samples, although in some cases a supposition can be made on the basis of the likelihood of features of 

the sample to be found in typical populations. In these cases, 

however, the resulting taxonomic assignment is qualified. 

The populations for which taxonomic assignment is 

most difficult are those in which the single morphologic 

mode falls approximately on the sharply defined boundary 

of a systematic diagnosis, such as the single population of 

Microtus paroperarius and Lasiopodomys deceitensis in the 

Cumberland Cave fauna of Maryland, discussed later in this 

report (p. 53). This large sample had been assigned to 

Microtus paroperarius by van der Meulen (1978), although 

nearly half the individuals have a frrst lower molar morphotype that is included in the definition of Lasiopodomys 

deceitensis. 
16 AUOPiiAIOMYS AND THE OLYOR SUITE, Y AKUTIA 

No Lasiopodomys morphotypes are present in the 

"typical" or type population of Microtus paroperarius from 

the Cudahy fauna of Kansas. However, because of van der 

Meulen's assignment of the Cumberland Cave population, 

including a high percentage of Lasiopodomys morphotypes, 

to M. paroperarius, samples of Lasiopodomys from other 

localities have been assigned to Microtus paroperarius 

(Guilday and others, 1984; Miller and others, 1987). In the 

Cumberland Cave case, no matter how large a sample and 

no matter how certain the statistical evidence of the mode 

being slightly on one side or the other of the defined 

boundary, to call the entire population by either name is a 

misrepresentation. 

Several devices, such as informal numbered stages of 

morphologic differences between named taxa or a slash 

between taxonomic names (instead of the dash used herein), 

have been used to indicate the intermediate morphologic 

position of particular populations between two named forms 

(Krishtalka and Stuckey, 1985; Bown and Rose, 1987; 

Repenning, 1987). 

The common opinion of all who have considered this 

problem is that the addition of new names for intermediate 

forms in such anagenetic evolutionary gradation would 

unnecessarily enlarge the nomenclature. Unfortunately, too 

many have not considered the problem and have simply 

introduced new names or expanded the definition of existing 

names to include atypical morphotypes. Thus the "typical" 

characterizations become obsolete, and confusion in nomenclature is begun. Only the morphological variations of the 

type population can be considered as "typical." 

Repenning (1987) used hyphenated names to indicate 

morphologically intermediate populations and this device is 

followed herein; such treatment would list "Microtus 

paroperarius-Lasiopodomys deceit ens is" in the Cumberland 

Cave fauna. The identification of this population as Microtus 

paroperarius by van der Meulen (1978) has caused misidentifications in other publications because it has been assumed 

that his identification indicated that the individual variation 

in this population from Cumberland Cave was typical of the 

species. 

Although awkward and not considered by the rules of 

nomenclature, use of a hyphenated double-name device calls 

attention to the fact that a population is not typical but has a 

variation that includes significant percentages of the morphotypes of two defined taxa. Furthermore, it suggests that 

the so-designated population is part of an anagenetically 

evolving lineage and that it is not a "typical" population of 

either name used. It should prevent the assumption that this 

great a variation is permissible under one name, under either 

applicable name. To give the intermediate population a new 

name is to compound the problem, and to list two species 

where only one population has existed is to hide the phylogenetic relationships. 

Herein, proportions of differing morphotypes representing between 40 and 60 percent of the population sample 

are described as hyphenated double-names; if proportions 

are unequal, the most abundant morphotype is named first. 

Populations with more than 60 percent of one morphotype 

are assigned to that genus and species, and the remaining 39 

percent or less are considered as individuals overlapping the 

morphology of another taxon. 

Such intermediate faunas are not common. Most populations fall clearly on one or the other side of the boundaries 

of taxonomic definitions. In this report the hyphenated, double-name device is used only once, for this population from 

Cumberland Cave. In the case of the Allophaiomys and Lemmiscus population from SAM Cave, New Mexico, morphotypes of Lemmiscus constitute only 21 percent of the 

population and the entire population is assigned to Allophaiomys, with the notation that its variability overlaps the morphology of Lemmiscus. 

The Cumberland Cave population of Microtus 

paroperarius-Lasiopodomys deceitensis certainly is not typical of either taxon; the type population of Microtus paroperarius from the Cudahy fauna of Kansas differs greatly 

from the population in Cumberland Cave and it is not clear 

why van der Meulen used this name. Similarly, the type population of Lasiopodomys deceitensis contains no Microtus 

morphotypes. Although 41 percent of the population has a 

Lasiopodomys morphology and 15 percent has a morphology typical of Lasiopodomys deceitensis, and although van 

der Meulen had specimens of Lasiopodomys deceitensis 

from the type population, Cape Deceit, Alaska, in his study 

collection, he appears to have failed to note the similarity. 

The SAM Cave, BOT -4 locality, population of Allophaiomys n.sp. certainly is not typical of Allophaiomys 

pliocaenicus, and a new species name is considered appropriate. But because only 21 percent of its individuals overlap 

the morphology of Lemmiscus the hyphenated name 

Allophaiomys-Lemmiscus does not seem appropriate. It 

would seem appropriate to mention in the diagnosis of Allophaiomys n.sp. that 21 percent of the type population has a 

Lemmiscus dental morphotype, and that up to 40 percent of 

overlap with the Lemmiscus morphotype could be tolerated 

under the name Allophaiomys n.sp. The population is not 

large enough to be confident of the exact percentage. What 

seems most inappropriate is to give a new name to each population that differs by a minor percentage in its overlapping 

morphotypes. That many names are neither needed, nor 

helpful, nor defendable. Contradictory morphotype proportions are discussed in the pages to follow with regards to the 

differences between the Hanover Quarry Fissure and Cumberland Cave faunas. 

The Microtus paroperarius-Lasiopodomys deceitensis 

population from the Cumberland Cave fauna has only one 

morphologic mode that is essentially intermediate between 

the two defined taxa; the population represents linear, 

anagenetic evolution from one artificial systematic definition into another. If a bimodal distribution of diagnostic 

character states is not found in an intergrading population, 
VARIABILITY AND EVOLUTION 17 

the population represents only one natural species, despite 

morphologic overlap of defined characters of two systematic 

species in the population. This is the crux of the incompatibility built into the Linnaean binomial classification: the 

attempt to subdivide the gradation of evolution into sharply 

defined systematic units. 

Bimodal distribution of diagnostic character states in a 

morphologically intergrading population has an entirely 

different significance. It indicates diversification. It does 

not indicate that the population has diversified nor does it 

indicate that it is about to diversify; it indicates that the population lived near the time of diversification, either before or 

after. Later faunas will show increasing polarity toward their 

separate complex of diagnostic character states. Populations 

with a bimodal distribution of diagnostic character states are 

considered as representing two taxa, even though it is not 

possible to know if they have evolved genetic isolation. 

Great individual variability is, of course, also present in 

faunas lacking Allophaiomys or Allophaiomys morphotypes. 

However, as Chaline (1966) noted, this overlap of morphologic characters decreases with time as populationsf species, 

and genera polarize in their phenotypic characters. Polarization in populations as a result of decreasing morphologic 

variability is a recognizable evolutionary trend and identifies 

genetic change. Degree and range of population variability 

are, thus, of taxonomic significance. An estimate of morphologic variability within the type population, thus, should be 

an essential part of any diagnosis. This report relies upon this 

variability as a tool to distinguish the evolutionary stage of 

any fossil population. 

Several fossil microtine species are essentially nomina 

vana, in Simpson's (1945) sense, because they are based 

upon a single specimen for which no population characteristics are available. This inadequacy may be provisionally corrected by reference of the species to a different population in 

which adequate population characteristics are evident, but 

such proxy characterization is always subject to correction 

by the later discovery of the character variation in the type 

population. Examples of this procedure in Pedomys llanensis and Pitymys hibbardi are discussed later. For both species, population characteristics have been provided by 

reference of the species to other faunas, but these characterizations are subject to nullification if a satisfactory type population should ever be discovered. 

VARIATION AND BIOCHRONOLOGY 

Recognition of the proportions of the morphologic variations of one microtine lineage in several faunas allows the 

several populations to be broken down into progressive evolutionary units of the lineage. These may be checked and 

verified against the population characteristics of other elements of the fauna, but, with most microtines, such similar 

populations are too closely spaced in time to be verified by 

any other means of approximating time. 

For example, in populations described as having both 

Allophaiomys and Terricola morphotypes (a very common 

association in Eurasia), the following are recognizable: (1) a 

"typical" Allophaiomys population (the type population, 

Betfia-2 fauna; fig. 14); (2) an advanced Allophaiomys population with a significant minority of individuals overlapping the Terricola morphology (Mt. Peglia-1 fauna); (3) 

an Allophaiomys-Terricola population with a morphologic 

mode near the sharply defined boundary of systematic diagnosis (possibly Razdolie fauna); (4) a primitive Terricola 

population in which a significant minority of individuals still 

overlaps the Allophaiomys morphology (possibly KarayDubina); and (5) a ''typical" Terricola population in which 

essentially all individuals have a Terricola morphology 

(living). With large samples, these can be further subdivided 

in terms of "more advanced" or "less advanced," but such 

estimates require stronger statistical evidence to be credible. 

Population analysis thus can provide a biostratigraphy 

in which one of five definable stages may exist in a fauna 

that usually would be described as containing both Allophaiomys and Terricola, a condition not true of any of the five 

stages given in the example above, because all have intergrading morphotypes and must be considered a single population, hence only one taxon. Each of the five stages is 

composed of a single natural species, and they differ only in 

their range of morphologic variation between systematic 

species. 

Such evaluation of the proportions of morphotypes 

within a sample of a population that is intergrading between 

two defined morphologies provides much more biochronologic discrimination than does referring the population to 

one or two artificial taxonomic categories. In the discussion 

of faunas that follows, the use of such population stages 

results in a temporal discrimination that appears to be sensitive to a period of about 5,000 years. However, such faunal 

variation can only be recognized in a sample large enough to 

suggest an approximate proportion of morphotypes. If only 

one specimen of Allophaiomys and one specimen of Terricola are in the sample, whether they represented an advanced 

Allophaiomys population, a primitive Terricola population, 

or two populations-one of Allophaiomys and one of 

Terricola-would be indeterminate. 

Morphologic gradation between two defined morphologies must be demonstrable in the sample to indicate individual variability in one population during linear evolution. 

Bimodal distribution of morphotype frequencies must be 

present to indicate diversification of taxa. Many faunal lists 

show, for example, both Allophaiomys and Pitymys, suggesting budding or accomplished diversification. However, 

study of morphotype frequency within such a sample usually 

shows a great majority of one morphotype and only a few 

specimens of the other, indicating the presence of only one 

taxon with great individual variability. The difference is biochronologically significant. 
18 ALLOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

In the present discussion, therefore, it is important to 

note that the presence of a few individuals with an Allophaiomys dental pattern, grading within the fossil (or living) population into the dominant morphology of a taxon recently 

derived fromAllophaiomys, is not considered an association 

of both descendant and ancestor. The reverse is also true: 

populations of Allophaiomys with a few individuals that 

overlap the characters of more derived forms do not constitute associations of both ancestral and descendant taxa. This 

is in contrast to nearly all published faunal lists, which customarily list both morphotypes as taxa of the fauna. This 

custom imparts an erroneous biologic and chronologie 

implication of two discrete taxa. 

Both of the preceding examples show the extent of variability and indicate either a probable past or future "hyphenated boundary" population in a linear sequence of evolution 

like that discussed from Cumberland Cave; or they may indicate a future bimodal distribution of characters and diversification into two lineages from one. But only one taxon is in 

the population used as an example. Hence, only one should 

be listed for the fauna. 

To list two taxa on the basis of two morphotypes in an 

intergrading population implies an entirely different stage 

and condition in evolution. Minor percentages of morphologic variants that overlap the defined morphology of 

another taxon may be acknowledged by the words "primitive" or "advanced," separated from the name by a comma, 

or they may be discussed in the text. 

Thus, the Cheetah Room fauna of West Virginia contains one intergrading population with 75 percent of its individuals having a Lasiopodomys deceitensis morphology and 

25 percent having a Microtus paroperarius morphology; the 

population should be listed as "Lasiopodomys deceitensis, 

advanced." In the same fauna occurs one intergrading population with 63 percent Pitymys and 37 percent Allophaiomys 

morphotypes, distributed in a distinctly bimodal patternthe majority of Allophaiomys morphotypes look "typical" 

and the majority of Pitymys morphotypes look "typical"; relatively few individuals appear intermediate. This population 

should be listed as "Allophaiomys sp. and Pitymys hibbardi. " In the Cumberland Cave fauna of Maryland an intergrading population with 41 percent Lasiopodomys 

deceitensis morphotypes and 59 percent Microtus paroperarius morphotypes is present, but one mode in morphotypes 

is present, and it falls close to the boundary of the two 

generic definitions; this population should be listed as 

"Microtus paroperarius-Lasiopodomys deceitensis." 

Note again that the recognition of one or more taxa cannot be made with a small sample because of the lack of statistical significance. Although not. discussed in this report, 

the fauna from Fyllan Cave, Texas (locality 19, fig. 1) presents an example (A.J. Winkler, written common., 1990). 

Four first lower niolars of Allophaiomys morphotype are in 

the sample and, morphologically, these could represent typical Allophaiomys pliocaenicus. They are associated with the 

North American bog lemming Synaptomys and are in 

reversely magnetized deposits; an age younger than the 

Cheetah Room fauna(== 840,000 yr B.P.) and older than the 

Brunhes Chron (==790,000 yr B.P.) is indicated. This bracketed range suggests that the fauna would be uniquely young 

for a fauna containing typical Allophaiomys pliocaenicus, 

although typical morphotypes of Allophaiomys pliocaenicus are known in younger populations of Pedomys llanensis 

(Pfaff, 1990). The sample could represent Allophaiomys 

guildayi, but it is too small to evaluate the nature of the population and demonstrate the. variability that characterizes this 

later species. 

The four specimens from Fyllan Cave should be identified only as Allophaiomys sp. even though the small sample 

is morphologically conformable with Allophaiomys pliocaenicus. An identification as Allophaiomys guildayi? could be 

justified on the basis of present knowledge of the history of 

this lineage and of the age of the Fyllan Cave fauna. The 

fauna appears to be too old to justify an identification as 

?Pedomys llanensis and too young to justify an identification 

as Allophaiomys pliocaenicus?. 

Possibly the only reason that variability appears conspicuous in the descendants of Allophaiomys is that its fossil 

record is very well documented. The author knows of no 

other mammalian group where consideration of recognizable evolutionary grades can lead to debating differences in 

age that may be as little as 5,000 years apart, as will be considered in some of the following faunal·discussions. 

It is difficult to conceive of a situation in the evolution 

of any mammal that does not involve considerable individual 

variability during speciation. However, the overall rate of 

evolution of a group must be reflected in the range of variability of a population. Depending upon what genera are 

recognized, the descendants of Allophaiomys averaged four 

or five genera (including all divergent lineages) evolving in 

about 1 million years (fig. 14) and a much greater number of 

species. Mammalian groups evolving at the rate of one new 

genus in 1 million years might be expected to show much 

less individual variability in individual populations; thus, the 

degree of population variability would seem to say something about the evolutionary rate of a lineage. 

MULTIPLE ORIGINS 

The degree of gradational variability observed in many 

fossil microtine faunas here considered displays the evolution of descendant genera out of ancestral Allophaiomys. 

These faunas occur throughout the Northern Hemisphere. 

Multiple origins, separated both geographically and temporally, are indicated. The lineages derived from North American populations of Allophaiomys are Lemmiscus, Pitymys, 

and Pedomys. One endemic lineage of Microtus evolved in 

North America out of immigrant Lasiopodomys, itself 
MULTIPLE ORIGINS 19 

derived from Allophaiomys in Asia. Terricola, Lasiopodomys, Phaiomys, Proedromys, Hexianomys, and most 

lineages of Microtus evolved out of Eurasian populations of 

Allophaiomys (or Lasiopodomys in the case of Microtus and 

possibly Proedromys and Hexianomys). Proedromys and 

Hexianomys are endemics of the Oriental faunal region. 

Pitymys and Pedomys are endemics of the eastern United 

States faunal region, and Lemmiscus is endemic both to the 

eastern and western regions of the United States. 

In North American localities only one derived lineage 

is seen to develop at one time and out of one population of 

Allophaiomys. The author has seen no multiple generic origins from single populations of Allophaiomys in Eurasian 

faunas, but these populations have not been so closely examined. These records suggest that when a population begins to 

change by shifting its range of variability, it follows one pattern only. Only evolution toward a single set of character 

states, characterizing only one derived lineage, occurs in any 

single population. Allophaiomys may evolve into Lemmiscus 

in a population of the highlands of New Mexico, and another 

population, perhaps at a different time, may evolve into 

Pedomys near sea level along the Atlantic Coast; but no population evolves in two directions to become two derived genera at the same time and out of the same population, and 

perhaps not in the same environmental situation. Different 

populations, usually at different times and often in different 

areas, evolve toward different derived lineages. 

As an example (fig. 14), in the Cheetah Room fauna of 

West Virginia, Lasiopodomys, derived earlier from Allophaiomys in Asia and an immigrant first to Beringia and then 

to the United States, is seen to have been experiencing a 

change in individual variation towards Microtus. This was a 

change that passed the midpoint of individual variation 

toward Microtus later, in the Cumberland Cave ·fauna of 

Maryland. Also in the Cheetah Room fauna Allophaiomys, 

also an immigrant from Asia but a million years earlier than 

Lasiopodomys, is seen to have evolved a bimodally split 

population containing two lineages, one a continuation of 

Allophaiomys and the other the first Pitymys. Allophaiomys 

finally became extinct in North America after the Cumberland Cave fauna lived by evolving a major Pedomys morphotype variation at about the same time that Lasiopodomys 

morphotypes had disappeared from Microtus populations (in 

the Trout Cave No.2 fauna of West Virginia). 

Later populations of Pedomys had increasingly minor 

percentages of Allophaiomys morphotypes in association 

with increasingly typical populations of Microtus paroperarius, which contain no Lasiopodomys morphotypes. A cording to Martin (1987) some individuals of living Pedomys 

ochrogaster still have an Allophaiomys dental morphotype. 

Pedomys and endemic Microtus rapidly dispersed westward 

to the east side of the Rocky Mountains but never left the 

eastern United States faunal province, in contrast to territorial reclusion of Pitymys. 

There is no microtine fossil fauna in the world known 

to the author in which one genus, as Allophaiomys, was 

simultaneously evolving into two others, as Lasiopodomys 

and Terricola. From published information, the Razdolie 

fauna of Western Siberia (Zazhigin, 1980) seems to :he the 

most likely to show this, but the author's examination of this 

fauna was too brief to be certain; from Zazhigin's (1980) 

published description and illustrations the Lasiopodomys 

appears to be established in the Razdolie fauna and the 

generic intergradation appears to be between Allophaiomys 

and Terricola. This represents a reverse historical sequence 

to that shown from the two faunas of Monte Peglia, Italy 

(van der Meulen, 1973), in which Allophaiomys frrst evolved 

into Terricola and then, in a later fauna, into Lasiopodomys. 

These examples from Monte Peglia are, however, clearly at 

different times and presumably from different populations of 

Allophaiomys; van der Meulen recognized them as different 

species of Allophaiomys. 

The lineages derived from Allophaiomys reveal few 

records of bimodal morphologic trends and none of multiple 

diversification at the scale of individual populations. But 

there are many examples of two lineages in the same fauna 

that have been derived from Allophaiomys, each showing 

different degrees and direction of population evolution away 

fromAllophaiomys. In such cases population structure indicates that one is more removed from Allophaiomys than the 

other (different times of derivation) and presumably all can 

be explained by the reintroduction of Allophaiomys from an 

adjacent province. 

Nearly all the examples considered here indicate anagenetic evolution from Allophaiomys into a derived taxon. 

Only one population from North America is known that 

shows bimodal distribution of morphotypes. This is the population of Allophaiomys and Pitymys in the Cheetah Room 

fauna, indicating a divergence of the genus Pitymys from 

Allophaiomys and the continuation of both Allophaiomys 

and Pitymys together. The populations of Allophaiomys and 

Lemmiscus n.sp. from several localities in SAM Cave, New 

Mexico, may indicate divergence of the two genera or linear 

evolution from Allophaiomys toward Lemmiscus, but the 

examination is not complete. The BOT -4 sample from SAM 

Cave contains only 13 first lower molars with a Lemmiscus 

morphotype, statistically a rather weak sample for drawing 

conclusions about population structure. A younger fauna is 

needed to show possible divergent bimodality, and the 

BOT -4 fauna appears to be the youngest in SAM Cave. The 

nearby and later faunas of Hansen Bluff, unfortunately, contain neither genus and do not help deCide whether the trend 

in SAM Cave was Allophaiomys into Lemmiscus or Lemmiscus branching from Allophaiomys and the continuation of 

both. 

There are many records of two populations within one 

fauna, each evolving from Allophaiomys into a different 

derived lineage; but in all cases considered the faunal sample 

indicates separate populations, one much farther along in 

evolutionary transition than the other. 
20 AUOPHAIOMYS AND THE OL YOR SUITE, Y AKUTIA 

In the Cumberland Cave fauna of Maryland, perhaps as 

little as 10,000 years younger than the Cheetah Room fauna, 

the remaining and last-recognized population of Allophaiomys in North America was evolving directly into the genus 

Pedomys, very similar to Pitymys. This took place in faunal 

association with a separate population of Pitymys having no 

individual morphologic overlap with Allophaiomys (as was 

the case in the Cheetah Room fauna). Only about 16 percent 

of the Allophaiomys population has a typical Pedomys morphotype; hence the Pitymys population of Cumberland Cave 

was more polarized in morphologic variation. It seems clear 

that the population of Allophaiomys in the Cumberland Cave 

fauna was evolving directly into a Pedomys morphotype and 

that the Pitymys population was morphologically stable 

(polarized). 

Diversification does not appear to result in the extinction of the ancestral taxon, but proceeds by morphologic 

divergence of part of one population toward a second 

defined morphotype, presumably because of some environmental constraint. The author believes that anagenesis 

within a single lineage is by far the most common pattern 

and that only it results in the extinction of the ancestral 

taxon. But such extinction occurs only in a provincial sense 

and the taxon may survive in other provinces. 

Thus it seems possible for an ancestor to become 

extinct through linear evolution in one faunal province and 

to become reintroduced from an adjacent province, although 

no such records are recognized (but some are suspected) in 

this report. The occurrence of Allophaiomys with descendant genera throughout the Northern Hemisphere indicates 

the persistence of an ancestral taxon, at times possibly 

through diverging morphotypes but probably more often 

from interprovincial faunal exchange subsequent to provincial extinction. 

Diversification of lineages also is more of a geographicprovincial event than a worldwide phenomenon, as usually 

conceived. This has been pointed out at least since 1969 

(Shaw), but the worldwide use of "frrst" appearances and 

"last" appearances in biochronology persists. The frequent 

occurrence of ancestral Allophaiomys with Lasiopodomys 

and Terricola, and of ancestral Lasiopodomys with Microtus, may indicate interprovincial exchange rather than diversification within one province. However, as discussed, 

where the origination of a taxon can be established by population characteristics, it appears to consist of the development of a new taxon from an ancestral stock, and never the 

termination of an ancestral stock by splitting into two 

descendant lineages. At least from the present record of population structure, Allophaiomys appears to have become 

extinct only through unimodal, anagenetic evolution into 

derived genera, including Pedomys in North America and 

presumably Phaiomys in Asia. 

The tribes Microtini and Pitymyini evolved more than 

once out of Allophaiomys, as presumed by Chaline (1966). 

The tribe Pitymyini has at least three separate origins out of 

Allophaiomys: Pitymys and Pedomys in North America and 

Terricola at least once in Eurasia. The tribe Microtini has at 

least an equal number of geographically and temporally 

separate origins: once in North America and at least twice in 

Eurasia, possibly more. These multiple origins raise questions of procedure and concept in systematic nomenclature. 

This report accepts multiple origins in its concept of classification until the history of a lineage is sufficiently well documented that its subdivision, by different origins, can be 

defended and morphologically identified. 

Multiple origins also raise questions of biochronologic 

significance. These multiple origins have occurred at different times and cannot have the same age significance everywhere. Such separate origins at different times will continue 

to raise questions until the mosaic of evolution into the living 

fauna is much better known. 

Only a small and early part of microtine history is 

revealed in the present discussion, but this small part is surprisingly complex (fig. 14). In the eastern region of the 

United States, the presence of Microtus paroperarius indicates an origination out of Lasiopodomys very close to 

830,000 years ago and about 400,000 years before the immigration of Microtus from Asia, but, as yet, the origin of no 

other species of the genus, as here defined, can be so closely 

dated. One lineage of Microtus, however, appears to have 

evolved in Asia possibly 1.5 million years ago, as it is 

present in the western province of the United States perhaps 

1.4 million years ago. Other lineages of Microtus may have 

evolved before 1.0 million years ago, to judge from the European fossil record; but their actual time of evolution has not 

yet been identified. 

The generalized temporal (not phylogenetic) sequence 

of genera that have evolved out of Allophaiomys appears to 

be: Terricola, Lasiopodomys, Proedromys, Pitymys, 

Pedomys, and Phaiomys. Microtus evolved out of Lasiopodomys, and did so at least three times. The history of Phaiomys is not known, and it could well be living Allophaiomys 

in which polarization of characters has changed it to a condition noticeably different from that of fossil Allophaiomys. 

Some rec~rds seem to result from a sequence different than 

that given above; Lasiopodomys seems more removed from 

Allophaiomys than does Terricola in Western Siberia. This 

may reflect the nature of the lineages, however, as the Pitymyini seem to retain Allophaiomys morpho types for a longer 

~me than do the Lasiopodomys lineages. 

These histories are discussed in the pages that follow 

and there the changes in population structure that led to them 

are arranged into biochronologies. The constructed biochronologies are applicable only intraprovincially, although dispersal history interlocks the provincial biochronologies at 

specific times. Most of the evidence presented is in the 

United States east of the Rocky Mountains, and there this 

biochronology is the most detailed. 
CLASSIFICATION 21 

CLASSIFICATION 

All taxa discussed in some detail are placed in one of 

three tribes of the subfamily Arvicolinae: the Arvicolini, 

Microtini, or the Pitymyini. The classification basically follows that of Kretzoi ( 1969) except that he did not use a tribe 

Pitymyini, which was used and explained by Repenning 

(1983); it has been outlined for all microtine (arvicolid) 

rodents in Repenning, Fejfar, and Heinrich (1990). The classification used here differs only in that the genus Lemmiscus 

is removed from the tribe Lagurini and placed in the tribe 

Microtini, as will be discussed. The definition used for the 

subfamily Arvicolinae is that used by Repenning and Grady 

(1988) and it was there diagnosed as "Cricetid rodents with 

hypsodont, triangularly prismatic cusps on their cheek teeth 

(microtine cricetids); m1 with posterior loop and three basic 

alternating triangles, differing from the Ondatrinae and 

Dicrostonychinae; Anteroconid Complex with single 

rounded to globular Cap, differing from the Prometheomyinae [and no or variable number of secondary triangles or 

wings]; M3 with alternating triangles differentiated, not 

lophate, differing from the Lemminae" [and lower incisor 

passing beneath the cheek teeth within the mandibular corpus, differing from the Dicrostonychinae and the Lemminae] 

(bracketed phrases added here). 

The subfamily Arvicolinae includes five tribes: Arvicolini, Microtini, Pitymyini, Clethrionomyini, and Lagurini. 

The Arvicolini are ancestral. The Pitymyini and the Microtim derive from the arvicoline genus Allophaiomys. The 

Clethrionomyini retain rooted cheek teeth (for the most 

part). The Lagurini derive from the lineage of the arvicoline 

genus Mimomys. Only the first three tribes listed at the 

beginning of this paragraph are discussed in the present 

report. This is the first publication to include the North 

American genus Lemmiscus in the tribe Microtini, rather 

than the tribe Lagurini; otherwise the generic content of 

these tribes is as listed in Repenning, Fejfar, and Heinrich 

(1990). 

The present report outlines the history and defines the 

taxonomic units of Allophaiomys of the tribe Arvicolini, the 

derived tribes Microtini, and (in less detail) Pitymyini, to 

illustrate and emphasize that the interpretation of the age of 

the Olyor Suite, as represented in the Krestovka Sections in 

the Kolyma Lowlands of Y akutia, cannot be made without a 

uniform nomenclature and without knowledge of the differing provincial histories of its taxa. 

This age interpretation cannot be made. simply by 

comparison of the microtine faunal lists from the Olyor 

Suite with those of some province elsewhere in the world 

without knowledge of the history of evolution and dispersal 

in all areas that might represent the source of the faunal elements. At present this information in the provinces of Asia 

and Beringia is sparse, although recent and current work in 

both areas is improving it rapidly (Zazhigin, 1980; Zheng 

and Li, 1990; Morlan, in progress). To make an age interpretation of the Olyor Suite, the application of taxonomic 

nomenclature must be uniform, the evidence of stage of 

evolution must be understood, dispersal patterns must be 

recognized, and provincial differences in the timing of evolution and of dispersal must be considered. 

The present report integrates the records from North 

America with those of Eurasia to provide the known background that is needed for the evaluation ofthe age ofthe Krestovka Olyor. Nevertheless, this global synthesis of history 

is incomplete at present and the size of the population samples from the Olyor Suite in the Krestovka Sections is minimal for the interpretation. The small sample and poorly 

understood history of adjacent Asia preclude the hope that 

such interpretation will have the precise biochronologic control that can be inferred for many localities in the eastern 

three-quarters of the United States. As is discussed herein, 

evidence for the history of Allophaiomys and its derivatives 

is weaker to the west of the Rocky Mountains in the United 

States than it is in the eastern three-quarters of the country. 

To synthesize this history, an entirely different classification than that currently conventional is used. It should be 

pointed out, however, that the classification here used differs 

little from that used before Chaline (1966) and Ognev (1948, 

1950). Both Ognev and Chaline explained their classification as being based upon that of Miller (1896), but an examination of Miller's 1896 classification shows almost no 

similarity to those of Ognev and Chaline. The main similarity of all three is that the genus Microtus includes many taxa 

that others have subsequently considered as separate genera. 

In the systematics of Miller, Ognev, and Chaline these taxa 

are held together by the common condition of rootless cheek 

teeth. 

Neither Ognev nor Chaline noted that Miller abandoned 

this classification in 1912, when he published his monumental treatise on the mammals of western Europe, or that the 

classification of Miller (1912) had been used throughout the 

world, with refinements by others (for example, Hinton, 

1923, 1926), until the time ofOgnev's and Chaline's publications. Other than mentioning Miller (1896), neither Ognev 

nor Chaline defended their classifications. However, the 

monumental size of Ognev's works and the revolutionary 

concepts of Chaline's works have had great impact, and their 

classification has been widely adopted, but not defended, 

since about 1970. 

The presently conventional all-inclusive genus Microtus comprises all forms from Allophaiomys pliocaenicus of 

the tribe Arvicolini (as defined by Kretzoi, 1954) to Microtus 

arvalis of the tribe Microtini (Simpson, 1945), as well as all 

forms in the other major Allophaiomys-derived lineage, the 

tribe Pitymyini (Repenning, 1983). To place all these in one 

genus hides their entire evolutionary history under a blanket 

of generic anonymity and excessive specific profusion. All 

taxa shown in figure 14 would have been included in the 

genus Microtus in the taxonomy of Chaline and Ognev. 

Equally defeating for historic-systematic clarification, 

the current proliferation of subgeneric, specific, and 
22 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

subspecific names, based upon individual variations within 

single populations, produces only hopeless confusion. 

There is little need to name a form intermediate in position 

between currently named taxa of one lineage, unless it 

serves to help identify some previously unrecognized ramification or evolutionary stage of this lineage. The purpose 

of taxonomy is to identify definable stages in a known history for ease in communication, not to produce names. 

Although the reasons usually are not specified, the genera Allophaiomys, Lasiopodomys, Microtus, Terricola, 

Pedomys, Phaiomys, Pitymys, and Proedromys and many 

other less well understood names are all included, as subgenera, in the genus Microtus by many modern microtine students, presumably following Chaline (1972) or Ognev 

(1950). This defeats the purpose of classification, as each of 

these above named genera (and probably many of those not 

named) has a separate history, represents a separate lineage 

(or lineages) directly or indirectly derived from ancestral 

Allophaiomys, and contains a number of species, fossil and 

living, that must be discussed in an understood phylogenetic 

context. Chaline ( 1966) demonstrated that his usage of genus 

Microtus was polyphyletic. 

The presently conventional, all-inclusive definition of 

Microtus includes more living species than the 20 or so other 

living microtine genera combined. As used by Chaline, and 

followed by many other microtine students, the size of the 

genus Microtus, and its admitted polyphyletic composition, 

demand division into several generic lineages. 

Those genera just listed, as well as Lemmiscus, are here 

recognized as full genera, as most of them were by. Hinton 

(1926). Other genus-group (subgenera of Chaline and 

Ognev) forms unnamed above, and here retained as subgenera of Microtus or Terricola, may also be recognized as distinct lineages when their history is further revealed. The 

history of each genus here recognized is known in varying 

detail, and begins between 700,000 and 2 million years ago. 

All but Allophaiomys still live, and Allophaiomys is extinct 

only in the sense that its individual variability has polarized, 

in the living Phaiomys, into a uniform pattern with remarkably little morphologic variability. As mentioned previously, 

such polarization indicates genetic change just as strongly as 

any other morphologic change, and should be equally recognized in classification. 

The ancestral genus Allophaiomys appears to be less 

than possibly 200,000 years older than the first derived 

genus, presumably Lasiopodomys from the Kudun fauna of 

Transbaikalia (Erbaeva, 1976; age interpretation from 

Repenning and others, 1990), in the Oriental faunal region; 

the oldest records of Allophaiomys that are dated by paleomagnetic events appear, at present, to be from pre-Olduvai 

faunas of China (Zheng and Li, 1990) and they appear to be 

about 2 million years old. Other records in Asia, undated by 

external evidence, may be older. By the beginning of the 

Olduvai event, Allophaiomys had dispersed to the United 

States and to Holland. 

Of those genera listed previously, Chaline's 1972 discussion of the classification of Microtus considered (as subgenera) only the genera Microtus, Allophaiomys, and 

Terricola (his Pitymys; subsequent work by Chaline and 

associates (1988) has emphasized, but not explained, the 

appropriateness of Terricola in Eurasia). Chaline also considered the subgenera Stenocranius, Jberomys, and Suranomys, which are here retained as subgenera of Microtus 

because their history is still unknown. 

Chaline's discussion of his classification was written as 

though he intended that it followed the tradition of Miller 

(1896). However, a comparison of Chaline's all-inclusive 

Microtus with Miller's all-inclusive Microtus reveals almost 

no similarity, as has been mentioned. Miller's (1896) Microtus included 12 subgenera, all but 2 of which (Microtus and 

Chilotus) have subsequently been considered as separate 

genera by most authorities, including Chaline. Thus, it 

would be incorrect to state that the systematic nomenclature 

of Chaline (1972) was based upon a return to a traditional 

concept. Miller's "traditional" concept of 1896 lasted 16 

years, until he published his monograph on western European mammals (1912). 

Chaline also s·tated that he followed the specialists of 

central and eastern Europe---Ognev (1950) and Kretzoi 

(1958), who had returned to the concept of Miller (1896). 

Ognev did use an all-inclusive genus (hardly that of Miller, 

however, but defended by the 1896 usage of Miller; Ognev, 

Vol. VI, 1948); but Kretzoi (1958) only said (emphasis 

added), "if groups as Pitymys or Phaiomys are only subgenera of Microtus (a very extended opinion among recent 

mammalogists)," and he did not advocate the usage in the 

cited report, although a year later (Kretzoi, 1959) he claimed 

that he did. 

As has been mentioned, neither Ognev nor Chaline 

mentioned that Miller himself abandoned his 1896 classification in his 1912 monograph on the mammals of western 

Europe, or that essentially all students of microtine rodents 

followed the classification of Miller (1912) until 1966. 

Following Miller (1912), later workers (including 

Hinton, 1926) recognized many of Miller's 1896 subgenera 

as separate genera. Ognev (1950), followed by Chaline 

(1972), eliminated many of the genera by placing them into 

Microtus, but by this time the list of subgenera included in 

Microtus bore little resemblance to that of Miller (1896). The 

distinctive character used to unify these genera as subgenera 

under Microtus was the same: Microtus has rootless cheek 

teeth. 

Miller's (1896) single exclusive character for Microtus 

was the presence of rootless cheek teeth in combination with 

a lack of the lemming position of the lower incisor. The popular depiction of these rodents as having "rootless cheek 

teeth" is, in a sense, incorrect; they differ from genera with 

"rooted teeth" only in that hypsodonty has evolved to the 

point where the animal dies before the teeth reach full maturity and form roots. 
CLASSIFICATION 23 

Rootless cheek teeth are no more diagnostic of lineage 

than are elongating dentine tracts. The increasing length of 

dentine tracts and the "rootless, condition are a single character; dentine tracts are a measure of hypsodonty and the 

rootless condition is simply the ultimate state of hypsodonty 

(Anderson, 1985). Young horses do not belong to a genus 

different than that to which old horses belong just because 

they have rootless cheek teeth. A classification that groups 

all microtines with no roots on their cheek teeth makes no 

more sense than a classification that groups all microtines 

that have dentine tracts. Hypsodonty is the diagnostic character; dentine tracts and rootless cheek teeth only help measure its development. Increasing hypsodonty is a feature that 

frequently evolved in many microtine lineages, as well as 

among other mammalian lineages. 

Zazhigin (1980) has treated Allophaiomys as a separate 

genus in recognition of its biostratigraphic significance, 

which is different than that of Microtus (sensu stricto), and 

because of its distinct dental morphology. Some neomammalogists (such as Corbet, 1978), have separated Pitymys 

from Microtus, following Ellerman and Morrison-Scott 

(1951) and as a convenience in classification. Repenning 

(1983) has recognizedAllophaiomys, Pitymys, Microtus, and 

a few smaller groups as separate genera because of their different histories as separate lineages; he has also recognized 

Lasiopodomys as an intermediate, phyletic genus between 

Allophaiomys and Microtus (Repenning and Grady, 1988). 

Pfaff (1990) also recognized Microtus, Pitymys, and 

Pedomys as full genera. Repenning (1983) further recognized two tribes to include the two major lineages derived 

from Allophaiomys and leading to Microtus and Pitymys: the 

tribe Microtini and the tribe Pitymyini. Many specialists 

continue to follow Chaline and include all of these, including 

the ancestral Allophaiomys, within the genus Microtus. 

As noted by Chaline (1966), Microtus and Pitymys are 

separable on morphologic grounds; in this Chaline followed 

the diagnoses of Hinton (1923), except that Hinton considered them as separate genera. As also noted by Chaline 

(1966, 1972, and 1974), Fejfar and Horacek (1983), Repenning and Grady (1988), and in the present report, in the earlier stages of the evolution of these genera out of 

Allophaiomys, continuous gradation occurs in the morphologic variation of the dental patterns between these forms 

and Allophaiomys; this is the nature of evolution. 

As discussed in the section, "Variability and evolution, 

(p. 12), separation of genera and species during the time of 

evolution between defined morphotypes can be made only 

on a statistical basis. Further, as in every case of complete 

morphologic gradation between taxa, there will be some 

individuals that are not certainly assignable to a taxon in any 

sample of two taxa in transition. Only the population can be 

so assigned on the basis of its modal morphology. 

Whether punctuated or not, evolution is a gradual process; anagenesis produces no sharp morphologic boundaries. 

No individual is greatly different than its parent or its 

offspring. On the other hand, classification is based upon 

ordered categories defined by theoretically sharp morphologic boundaries. Taxonomic nomenclature is the language 

of classification but is intended to reflect evolution; an 

incompatibility is built into the procedure. The only 

recourse provided by the rules of nomenclature is the authority of the type, and, as pointed out in the present report, its 

population. 

In the pages that follow, the definitions of the abovenamed genera are reviewed in terms of closeness to "typical, 

dental morphology. As has been explained, "typical, dental 

morphology is the most common morphology of the named 

species in the type population as sampled at the type locality. 

If the name Allophaiomys pliocaenicus is applied to any 

population other than the type population, it must include a 

similar range of variability, including a good percentage of 

individuals with recognizable pitymyinine characters; and 

about 3 percent of its individuals must have a Terri cola morphotype, otherwise that population did not have the same 

genetic composition as the type population. 

The concepts of both the most abundant individual morphology of the type sample and the limiting range of variation recognized in the type population are included in the 

word "typical." Both morphology and variability are needed 

to judge stage of evolution and identity of the taxon represented by the population sample. As will be illustrated, in 

species as individually variable as microtine rodents, it is difficult or impossible to positively identify named species 

from a single specimen; the nature of the population is 

critical. 

An example will best illustrate the taxonomic significance of variability. The type population of Allophaiomys 

pliocaenicus from Betfia-2, Romania, discussed more fully 

in the following section, has wide variation in morphologic 

characters (fig. 3; the morphologic characters used are 

shown in figs. 3 and 10). The most common morphology is 

one that has a simple rounded Cap on the Anteroconid Complex of the first lower molar and two widely confluent Primary Wings (forming the "Pitymys rhomboid, or "Pitymyan 

rhombus, of authors), the Wings are also broadly confluent 

with the Cap. This is the morphology that most workers 

associate with the genus; it is the "typical" morphology. 

The type population also includes some variants that 

are similar to the morphology of the living Phaiomys leucurus (also in the tribe Arvicolini). Because of these variants 

Martin (1989) placed the species "pliocaenicus, in the 

genus Phaiomys (his subgenus). But living Phaiomys leucurus has this morphology in a great majority (all?) of its individuals, whereas the type population of Allophaiomys 

pliocaenicus has only 7 percent of its individuals showing 

this morphology. 

Similarly, the type population of Allophaiomys pliocaenicus has a small minority of individuals with a reduced 

Dimension B-B', constricting or closing the confluence 

between the Primary Wings and the Cap. A few weakly 
24 AUOPHAJOMYS AND THE OLYOR SUITE, YAKUTIA 

suggest a developing Dimension A-A'. These are the character states of the genus Terricola (tribe Pitymyini), and in 

one individual the typical morphology of Terricola arvaloides is present in the type population. Kretzoi (1958) recognized this morphology and listed this species as being 

present in the Betfia-2 fauna (where it is still listed, as Pitymys arvalidens, in some records, for example, Maul, 1990). 

Van der Meulen (1973) recognized that this individual was 

simply an extreme variant of Allophaiomys pliocaenicus in 

the type population from Betfia-2 and that the fauna should 

not be listed as including Terricola. To include this genus in 

the faunal list from Betfia-2 would indicate a much younger 

age than otherwise indicated. 

Because of the presence of these Terricola variants, the 

nomenclatorial reasoning of Martin (1989) would seem to 

say that the species Allophaiomys pliocaenicus also belongs 

in the genus Terricola, as this morphology is also present as 

an individual variation in Betfia-2. This, of course, cannot 

be done, and its inappropriateness illustrates the point that 

the "typical" morphology, not the morphology of minor variants, must be used in making taxonomic assignments. To 

identify the typical morphology some sort of statistical procedure must be applied to the type population; in many cases 

a visual inspection of the sample will be conclusive, but variability must be estimated, and that variability must be named 

as a character of the species. Without consideration of population variability, the less variable species Allophaiomys 

deucalion would have to be considered a synonym of A. pliocaenicus. 

Thus the type population of Allophaiomys pliocaenicus 

is characterized both by a typical morphology, unique to the 

taxon, and by individual variability overlapping the morphology of living Phaiomys and living Terri cola. However, 

A. pliocaenicus differs from both of these other genera in 

that only a small percentage of its type population has these 

atypical morphologies and the vast majority exhibits its 

unique typical morp4ology. From typical Phaiomys and 

Terricola it also differs in having a very great range of individual variability. These features of variability are obviously 

diagnostic. 

The degree and direction of variability are genetic 

differences as surely as is the uniqueness of the "typical" 

morphology, and this difference should be considered in taxonomy. It is expressed by population characteristics and is 

not evident in the single type specimen. Different degrees 

and vectors of individual variability speak against synonymy. Thus the authority of the type specimen is extended to 

the type population. 

Morphologic and directional limits to recognized taxa 

must be specified for the purposes of uniform classification. 

Thus the origin of a taxon is here defined as the geologically 

earliest appearance in more than 60 percent of a population 

of a character, or character state, that consistently separates 

it from its anagenetically related taxon. Again, population 

characteristics, not type specimen characteristics, are the 

primary basis for taxonomy in lineages showing great 

individual variability. 

As discussed previously in the section on variability, 

the recognition of the evolution of a derived taxon begins 

with a hyphenated, double-taxon identification to indicate its 

intermediate position between populations of two defined 

morphotypic species (which may bridge two genera). This 

technique is intended to deter accidental broadening of the 

diagnosis of either ancestral or descendant taxa. The same 

form cannot be identified as different species of different 

genera in different fossil localities and still be expected to 

make any evolutionary or biochronologic sense. 

The following discussion reviews some of the more significant localities showing morphologic intergradation 

between the taxa present, and of the logic for the recognition 

of these taxa. Although some examples are discussed which 

could be given new names, such as "Allophaiomys n. sp." 

from SAM Cave, New Mexico, no new generic or specific 

names are introduced; only existing, published nomenclature 

is used in an attempt to present a very complex history as 

simply as possible. New names can be introduced in more 

detailed discussions of specific faunas. A complete review 

of these taxa and lineages i~ not attempted here, and the discussion of several taxa that do not bear on the age of the 

Olyor Suite is brief. Nevertheless, they must be mentioned 

to illustrate the nature of the faunas discussed and the pattern 

of the evolution of Allophaiomys. 

SYSTEMATICS: PHILOSOPHY, 

PROBLEMS, APPLICATIONS 

TRIBE ARVICOLINI, KRETZOI, 1954 

Revised dental diagnosis. -Genera of tribe Arvicolini 

(of subfamily Arvicolinae: Kretzoi, 1969; Repenning and 

Grady, 1988) have a first lower molar with posterior loop, 

preceded successively by three substantially closed and 

alternating triangles and terminated by an Anteroconid Complex with confluent, lingual and buccal Primary Wings and 

an uncomplicated, more or less globular Cap. Most genera 

have rooted cheek teeth, and dentine-tract elongation characterizes increasing hypsodonty. 

Generic contents of the tribe.-Genera currently 

included in tribe Arvicolini are Allophaiomys, Aratomys, 

Arvicola, Atopomys, Cromeromys, Hibbardomys, Mimomys 

(including many subgenera), Nebraskomys, Polonomys, 

Promimomys, Prosomys, Phenacomys, Phaiomys, and 

Villanyia. 

[Note: Because it has a complicated Anteroconid Complex in nearly all species, Phenacomys should not be 

included in tribe Arvicolini. A new tribe will not be introduced in this discussion, however. It is also not certain in the 

author's mind that Hibbardomys represents a single lineage, 
GENUS ALLOPHAIOMYS 25 

although the forms that have been assigned to this genus certainly belong in this tribe.] 

By having a first lower molar with a posterior loop, 

three basic alternating triangles, and an Anteroconid Complex with a simple, single-cusped Cap and confluent Primary 

Wings; a last upper molar with two or three triangles and a 

simple posterior loop; and a lower incisor that passes 

beneath the cheek teeth, Allophaiomys belongs in tribe Arvicolini of subfamily Arvicolinae. This is where . Kretzoi 

(1954, p. 355) placed the genus when he recognize4 and 

named the tribe; he also included Phaiomys and Arvicola. 

These three genera are the only rootless arvicolines. The 

rootless descendants of Allophaiomys compose the tribes 

Microtini and Pitymyini; the descendant Phaiomys remains 

in the Arvicolini. 

Phaiomys and Arvicola are the only living, rootless 

members of tribe Arvicolini and belong in this tribe because 

of their diagnostic dental characters; they belong to neither 

the Microtini nor the Pitymyini, which have more complicated Anteroconid Complexes. As mentioned, they and 

extinct Allophaiomys are unique within the tribe Arvicolini 

in having advanced to the stage of hypsodonty at which they 

have "rootless" cheek teeth. When one accepts the minor significance of the lack of tooth roots, Allophaiomys, Phaiomys, 

and Arvicola are recognizable as typical arvicolines. 

Enamel-thickness differentiation in the tribe Arvicolini 

may be of "Mimomys," intermediate, or "Microtus" types. 

The earliest genera and species of the tribe have either intermediate or "Mimomys" enamel-thickness differentiation; the 

youngest (living) genera and species of the tribe almost universally have "Microtus" enamel-thickness differentiation. 

Between these two points the nature of the enamel differentiation is variable. 

GENUS ALLOPHAIOMYS KORMOS. 1932 

Type species.-Allophaiomys pliocaenicus Kormos, 

1932. 

Revised dental diagnosis.-A genus of the tribe Arvicolini with rootless molars and length of first lower molar 

3.0 mm or less; Dimensions A-A', B-B', and C-C' never 

strongly constricted in over 40 percent of a population. 

"1YPICAL .. ALLOPHAIOMYS 

ALLOPHAIOMYS PUOCAENICUS KORMOS. 1~32 

(fig. 3) 

Type locality.-Betfia-2, Romania (locality 3 in fig. 1). 

Revised dental diagnosis.-A species of the genus 

Allophaiomys with the Cap of the Anteroconid Complex 

uncomplicated by posterolingual comer or other modifications in the "typical" morphology but having a posterolingual comer in about 7 percent of the type population. 

Reduction of Dimension C-C' lacking, Dimension B-B' 

greatly reduced in 3 percent and some reduction evident in 

about 30 percent, and Dimension A-A' noticeably reduced 

in 20 percent of the population; these variations result in 

about 3 percent of the population having a Terricola morphotype. There is no Microtus morphotype or character state 

tending toward the Microtini. 

Discussion.-The dental pattern of Allophaiomys pliocaenicus is similar to that of the ancestral genus Mimomys, 

but A. pliocaenicus has rootless cheek teeth. Allophaiomys is 

also similar to the significantly larger genus Arvicola, as 

noted by Kormos (1932), but Arvicola evolved out of 

Mimomys much later than Allophaiomys (von Koenigswald, 

1973), actually after Allophaiomys had become extinct. 

The frrst lower molar of the type species, Allophaiomys 

pliocaenicus, is rootless and well cemented; it consists of a 

posterior loop, three basic alternating triangles, and an 

Anteroconid Complex composed of two prominent, confluent Primary Wings and a smoothly rounded Cap with moderate variability (fig. 3). The Cap is often skewed lingually 

(fig. 3B, C) and in a few individuals shows weak indentations marking the position of reentrants that separate Secondary Wings in more derived genera (fig. 3G); these 

indentations also mark the beginning of a Dimension A-A' 

(well developed and marked in fig. 1 0). Dimension C-C' 

(marked in fig. 3A), between the apices of the reentrant posterior to the lingual Primary Wing and anterior to the buccal 

Primary Wing, is wide to only slightly narrowed so that the 

dentinal confluence between the buccal and lingual Primary 

Wings is complete to great. Dimension B-B' (marked in fig. 

3E and 1), across the neck between the Primary Wings and 

the Cap, is moderate to broad. Enamel differentiation is primarily intermediate. The length of the first molar usually is 

3.0 mm or somewhat less. 

The last upper molar of Allophaiomys pliocaenicus is 

"simple" and consists of an anterior loop, two to three alternating triangles, and a posterior loop that may or may not be 

extended posteriorly, but never develops a hook at its posterior end. 

Population variability.-Kormos (1932) described two 

species from the type locaiity, Allophaiomys pliocaenicus 

(the type species) and Allophaiomys laguroides; but the 

present author follows van der Meulen (1973) and considers 

them synonymous. 

With the exception of the last upper molar of "Allophaiomys laguroides" in figure 3 (fig. 3L copied from 

Kormos), the illustrations of this species from the type population of Allophaiomys pliocaenicus, from Betfia-2, 

Romania (10 M/1), were provided by 0. Fejfar of Prague. 

Van der Meulen (1973) illustrated 20 frrst lower molars 

from this population, and others are published by Kormos 

and by others. These illustrations form the basis for statements regarding population variability; the type population 

has not been reviewed. 

Based on this "sample" of about 30 frrst lower molars 

(some of the previously published illustrations are obviously 

duplicates of the same specimens), typical Allophaiomys 
26 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

A D E 

I J 

Figure 3. Allophaiomys pliocaenicus Kormos from Betfia-2 (Puspokfurdo), Romania. A-J are first lower molars; K and L are 

last upper molars; all are occlusal views and anterior is upward. The posterior loop of the first lower molars extends lingually; 

the posterior salient angle of the last upper molars extends lingually. Dentine is black, enamel is white, and cementum is 

stippled. K is a "rhomboid" M\3 of A. laguroides redrawn from Kormos ( 1932). All figures except K were made from drawings 

provided by Oldrich Fejfar. C-C', Dimension recording degree of closure of confluence between Primary Wings, is indicated 

on A. B-B', Dimension recording closure of confluence between Cap and Primary Wings, is shown on E and /; it is narrow on 

E and wide on I. Other named features of tooth morphology are shown in figure 10. Specimens A, D, and E were marked ''Allophaiomys laguroides" in Kormos' handwriting. Note individual variation in the Cap. HNHMB specimens. 
GENUS AUOPHAJOMYS 27 

pliocaenicus has little modification of the Cap. It lacks a 

high percentage of individuals with weak development of 

Secondary Wings or shortening of Dimension B-B'. At least 

63 percent show no modification at all; the Cap is a simple 

circular or rounded structure. In most individuals there is a 

wide confluence between the Cap and the Primary Wings, 

but in about 30 percent Dimension B-B' is noticeably 

reduced (partly a factor of less wear), and in 3 percent this 

dimension is essentially closed-a Terricola character state. 

In about 7 percent of the specimens, an angularity at the posterolingual comer of the Cap is developed, similar to that in 

several North American advanced populations and in living 

Phaiomys leucurus. Thirteen percent have an angularity at 

the posterobuccal comer of the Cap, a condition that is less 

common in advanced North American populations but is 

rather frequent in some Eurasian populations that are 

approaching Terricola. 

In about 20 percent of the type sample, a weak development of Secondary Wings coupled with a minor reduction of 

Dimension B-B' suggests the Terricola morphotype, and 

one specimen clearly is of this morphotype (3 percent). Kretzoi (1941) listed this specimen as Pitymys arvaloides (until 

quite recently Terricola was included in Pitymys), but van 

der Meulen (1973) noted that it was only an extreme variant 

of Allophaiomys pliocaenicus, an opinion that is obvious 

from the above inventory of variations. However, the name 

is still carried in faunal lists, as Microtus (Pitymys) arvalidens (Maul, 1990). 

Specific preoccupation of Pitymys arvaloides by 

Microtus arvaloides came into effect with the inclusion of 

the genus Pitymys in the genus Microtus by Ognev (1950), 

and Pitymys arvalidens was suggested as a substitute if this 

was done (Kretzoi, 1958). The recognition of Pitymys and 

Terricola as separate genera in the present publication 

requires the recognition of the name Kretzoi first applied to 

the Betfia-2 individual. There is now in use, as there was 

from 1923 until1958, both Microtus arvaloides Hinton and 

Terricola arvaloides (Hinton), but Terricola arvaloides is 

not present in the Betfia-2 fauna, except as a rare morphotype variation of Allophaiomys pliocaenicus. 

The individual variation of the type population of Allophaiomys pliocaenicus includes variations in the direction of 

the Terricola morphotype, and a small percentage ofindividuals (one individual) overlaps this morphology. There are no 

individuals in the sample in which Dimension C-C' is 

reduced, a reduction that would suggest evolution toward the 

tribe Microtini. 

Morphologic evolution.-Earlier records throughout 

Eurasia suggest that the Pitymyini, represented by Terricola 

(=Pitymys in former reports), is the first lineage to have 

evolved out of Allophaiomys. 

If the age (during the Olduvai event) inferred by Repenning and others (1990) for the Kudun fauna south of Lake 

Baikal (Erbaeva, 1976) is correct, this record is an exception 

that is earlier than the oldest known Terricola. 

Van der Meulen (1973) described an interesting 

sequence of faunas from the Monte Peglia locality of Italy 

which supports the earlier derivation of Terricola out of 

Allophaiomys. He divided the Monte Peglia collections into 

lower and upper faunas, herein called Monte Peglia-1 and 

Monte Peglia-2, respectively. Based upon his figured specimens, the lower faunas contain an advanced species of Allophaiomys that he called "sp. A" because he believed that the 

form was being named by Chaline (1972); the present author 

does not know which of the species subsequently named by 

Chaline was being considered by van der Meulen. "Sp. A" of 

van der Meulen (1973) contained 22 percent typical Allophaiomys variants, 44 percent pitymyinine-like variants with 

a weak but clear lingual Secondary Wing, and 34 percent 

Terricola morphotypes with a conspicuously shortened 

Dimension B-B' and some development of both Secondary 

Wings. "Sp. A" is decidedly advanced over typical Allophaiomys pliocaenicus and showed the same direction of 

morphologic drift, toward the Pitymyini; the morphotype 

percentages just cited would indicate that it would be reasonable to assign "sp. A" to the genus Terricola. No individual 

showed a reduction of Dimension C-C', leading toward the 

Microtini, in Monte Peglia-1. 

A different condition is indicated in van der Meulen's 

illustrations of the species from the younger fauna samples 

of Monte Peglia-2, which he called "sp. B" in the belief that 

it might be synonymous with Allophaiomys ruffoi Pasa 

(1947). Half of these specimens showed a reduction of 

Dimension C-C', which is leading toward the Microtini, and 

one-third had an acceptable Lasiopodomys morphotype. An 

exceptionally deep lingual reentrant angle 4 (between the 

lingual Primary Wing and the Cap) is present on nearly all 

specimens. One specimen (8 percent, only 12 specimens 

were illustrated) conformed to the "typical" Allophaiomys 

pliocaenicus morphotype. Based upon the illustrated sample 

from Monte Peglia-2, the population of Allophaiomys sp. B 

could be called "advanced Allophaiomys-Lasiopodomys. " 

Allophaiomys sp. B from the Monte Peglia-2 fauna is 

decidedly advanced over typical Allophaiomys pliocaenicus 

and shows morphologic drift toward the Microtini, overlapping Lasiopodomys in one-third of the sample. None 

showed a complete reduction of Dimension B-B' or the 

development of a weak buccal Secondary Wing, that would 

suggest Terricola. However, in the illustrated sample of A. 

sp. B, from Monte Peglia-2, 58 percent had a noticeable 

inflection of the anterolingual margin of the Cap (lingual 

reentrant 5), a feature which suggests the LasiopodomysMicrotus transition in other faunas to be discussed, primarily 

in North America. Although not so in the closure of Dimension C-C', the character state of this weak reentrant is more 

advanced than in "Microtus ex gr. 'oeconomus'" described 

by Markova (1990) from the Karay-Dubina fauna of the 

Ukraine. This provides a suggestion that there may be a separate origin of the Microtini in the European fauna, marked 

by different rates in character change. 
28 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

Considerable time would seem to separate "sp. A" and 

"sp. B" in the Monte Peglia faunas, and probably Terricola 

evolved during this time, although no recognized pitymyinine specimens were found with "sp. B." The lack of Terricola in the younger fauna could be related to latitudinal shifts 

in climate or unknown ecologic preferences of different 

populations of Allophaiomys. Like Allophaiomys, Terricola 

avoided colder climates that were tolerated by Microtus and 

Lasiopodomys. 

Identification.-The microtine rodent genus Allophaiomys was named by Kormos (1932) from an ample number 

of specimens collected at Betfia-2, known to Kormos as 

Puspokfurdo, southeast of Oradea in the Muntii Bihor, western Romania. Its name indicates that it is similar to the living 

genus Phaiomys, the type species of which is Phaiomys leucurus Blyth (1863). Kormos named several features of the 

skull and mandible that separate Allophaiomys from Phaiomys leucurus and also some features of the dentition. On 

the basis of dental similarity (7 percent of the type population have a posterolingual angularity on the Cap as does 100 

percent of Phaiomys), the two genera have been considered 

synonymous by Martin (1989), but Martin did not discuss 

the diagnostic characters given by Kormos or those in this 

report; in fact, he made no attempt to explain why he considered them identical. 

The sample of the living Phaiomys leucurus examined 

for this study (six specimens from the type region ofLadak, 

Kashmir) was not large enough to define population characteristics, but all living individuals seen have the following: 

1. "Microtus" enamel-thickness differentiation (the 

enamel on the anterior wall of the triangles of the lower 

cheek teeth is thicker than that on the posterior wall), 

whereas "intermediate" enamel-thickness differentiation 

(enamel thickness equal on anterior and posterior walls of 

the triangles) is by far the most common condition in "typical" Allophaiomys pliocaenicus. 

Many advanced populations of Allophaiomys have 

dominant "Microtus" differentiation; van der Meulen (1974) 

hinted that the primitive Allophaiomys deucalion has 

"Mimomys" enamel-thickness differentiation in more than 

50 percent of his sample (he said the specimens "more often" 

have "Mimomys" differentiation, but it is not absolutely clear 

that he referred only to the A. deucalion sample; he might 

have meant "more often" than the type population of A. pliocaenicus); A. deucalion was not examined for the present 

study. 

2. A persistent posterolingual angularity on the Cap 

of the Anteroconid Complex of the first lower molar (M/1) 

in all individuals; this is in the position of the lingual Secondary Wing of more advanced genera, and this feature is 

present only in a small minority (7 percent) of individuals of 

typical Allophaiomys pliocaenicus. In certain populations of 

advanced Allophaiomys in both Eurasia and North America, 

however, the posterolingual angularity of the Cap is a dominant character state. 

3. No third buccal salient angle at the anterior end 

of the third lower molar (M/3 ), as is present in some typical 

Allophaiomys (largely or entirely those smaller specimens 

that Kormos assigned to Allophaiomys laguroides). The significance of this difference is uncertain. 

4. A posterior loop on the last upper molar (M\3) 

that is consistently reduced from the condition in most individuals of Allophaiomys, whether advanced populations or 

not. 

And most significantly, as mentioned previously: 

5. A dental pattern variability that is conspicuously 

less than that of either typical or advanced Allophaiomys 

(fig. 4). 

These differences all seem explainable as the result of 

genetic polarization in living Phaiomys, a polarization not 

seen in the nearly 2 million-year-old typical Allophaiomys or 

any known population of this genus. It is not argued whether 

such polarization can be considered as significant in specific 

or in generic separation, but it is stated that it has resulted in 

character differences that clearly separate Phaiomys from 

Allophaiomys. The primitive condition of some of these 

characters persisted in younger populations of Allophaiomys, and others evolved toward the condition of living 

Phaiomys. 

Note that continued reduction of the posterior loop of 

the last upper molar would produce the most distinctive 

character of the Chinese genus Proedromys (Hinton, 1926, 

fig. 33; Zheng and Li, 1990, fig. 21). However, this genus 

is in the tribe Microtini because the structure of the first 

lower molar is advanced relative to either Allophaiomys or 

Phaiomys. 

A confusing and not fully explainable misconception of 

the identity of Phaiomys was adopted by Ognev (1950). 

With his inclusion of the genus Phaiomys in the genus 

Microtus, as well as many other former genera, the species 

leucurus became the junior homonym of Microtus leucurus 

(included in M. nivalis by Corbet, 1978). The name Phaiomys blythi ( = Arvicola blythi Blanford) was then applied to 

the type species. In addition, modifying Ellerman (1940-

1941) but apparently before the emendations of Ellerman 

(1949) were seen, Ognev also included species in Phaiomys 

(his subgenus of Microtus) that had been placed in 

Lasiopodomys or Neodon by some others (brandtii Radde, 

vinogradovi Fetisov, carruthersi Thomas, and juldaschi 

Svertsov). Although carruthersi and juldaschi had earlier 

been assigned to Phaiomys by other authors and are included 

in the tribe Pitymyini herein, Ognev appears to have been the 

first to assign brandtii and vinogradovi (=mandarinus in 

Corbet, 1978) to the genus (his subgenus) Phaiomys, and 

they are herein returned to Lasiopodomys and the tribe 

Microtini (Corbet, 1978, returned them to this lineage as 

species of Microtus). 

Ognev's assignment of brandtii and mandarinus 

(=vinogradovi) to Phaiomys was not followed by Gromov 

and Polyakov (1977), who returned these species to 
GENUS AUOPHAIOMYS 29 

~ 

~ 

0 

~ 1 2 mm 

B 

Figure 4. Phaiomys leucurus Blyth from the region of Ladak, Kashmir. Left lower dentition illustrated on the left side of each specimen; 

right upper dentition on the right A, USNM 198541. B, USNM 84033. C, USNM 84034. Note weak posterolingual angle on Cap of first 

lower molar and reduction of the posterior loop of last upper molar. Also note slight individual variability. 

Lasiopodomys, which they recognized as a full genus. These 

authors, however, were uncertain of the definition of Phaiomys, and placed the type species, Phaiomys leucurus, in the 

subgenus Neodon of the genus Microtus. Their uncertainty 

may reflect some feature of the Moscow collections, as the 

specimen they illustrated (1977, fig. 39) is not Phaiomys leucurus, but is a form belonging in the tribe Microtini and in 

the genus Lasiopodomys of the Oriental faunal region (which 

includes part of the former U.S.S.R.); they did not indicate 

where it came from, and the individual could represent either 

of the two living species of Lasiopodomys. (Compare with 

this report, fig. 11N and 0.) If this error reflects an error in 

the Moscow collections, it may explain Ognev' s confusion. 

Phaiomys leucurus Blyth has a simple, rounded Cap 

and completely confluent Primary Wings; it belongs in the 

tribe Arvicolini (Kretzoi, 1954). Lasiopodomys brandtii 

(Radde) has a cap with Secondary Wings and complete closure between the Primary Wings and belongs in the tribe 

Microtini. The genus Phaiomys does not occur in the former 

U.S.S.R., although a number of specialists believe that it 

does (Ognev, 1950; Chaline, 1974). 

As mentioned on page 25, two species from Betfia-2 

were named by Kormos: Allophaiomys pliocaenicus, the 

generic type species, and A. laguroides, a slightly smaller 

species that differs in some dental characters from the 

sample of A. pliocaenicus (fig. 3). Chaline (1966) found 

morphotypes of both species in the French localities of 

Balaruc and Mas Rambault and reported individual variation 

in dental-pattern morphology that bridged the differences 

between the two morphotypes. He therefore placed the 

species A. laguroides into synonymy with A. pliocaenicus. 

No consideration was made by Chaline of a possible 

bimodal distribution of the characters that might have separated the two species; it thus remains possible that two species existed in these French populations and that these were 

united by overlapping individual morphologic variation in a 

minor number of individuals (as in the type population). 

Chaline ( 197 4) later resurrected P. laguroides on the basis of 

its M\3, but Chaline's 1966 synonymy is here followed 

because van der Meulen ( 1973) could not separate the two 

species in the topotypic material from Betfia-2-and they 

are very similar (fig. 3). In the sample of the type population 

in Budapest, the specimens are labeled in Kormos' handwriting, indicating which species is represented. 

Chaline's later (1974) reinstatement of laguroides, as a 

subspecies of Allophaiomys pliocaenicus, was on the basis 
30 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

of Kormos' type having a "rhomboid" M\3. Chaline did not 

indicate whether individuals from Betfia-2 other than the 

type specimen had this "rhomboid" M\3. The "rhomboid" 

M\3 (a "simple" M\3; this report, fig. 13K) is an individual 

variant found in many populations of Allophaiomys throughout the Northern Hemisphere as well as in derived species; it 

is a variable character of the southern species of European 

Terricola, some of which have a "rhomboid" M\3, and, in 

North America, it is typical of Pitymys and Pedomys. In the 

present study, it was not determined whether the "rhomboid" 

M\3 was consistent in Allophaiomys laguroides and, as was 

done by Chaline (1974), the M\3 of"A.laguroides" is illustrated in figure 3 by redrawing the figure published by Kormos (1932). 

Temporal correlation.-As noted in the Introduction, 

the oldest dated records of Allophaiomys are from Zone IV 

deposits of China (Zheng and Li, 1990). These records are 

dated as older than the Olduvai Normal-polarity Subchron 

(more than 1.9 Ma). Other records in Asia may be older, but 

are not dated by age control external to faunal interpretations; none seem as old as the Gauss Chron (ending 2.48 Ma; 

present report, fig. 14). 

The age of the Betfia-2 locality is not known by evidence external to the nature of the fauna and its inferred biochronologic significance. The fauna is usually considered as 

being an early Biharian fauna in Europe, but not the earliest 

Biharian fauna (Fejfar and Horacek, 1983 ). Earliest Biharian 

faunas of Europe (considered latest Villanyian by some 

authors) include Kamyk (Poland), Villany-5 (Hungary), 

Betfia-13 (Romania), andZuurland (Holland); these contain 

a typically Villanyian fauna except that they also contain 

Allophaiomys. 

The differing assignment to European micromammal 

stages (latest Villanyian or earliest Biharian) derives from 

differing approaches to the biochronologic definitions. 

Some authors rely upon the total composition of the fauna 

and so refer these faunas to late Villanyian because, other 

than Allophaiomys, the faunas are typical of advanced 

Villanyian faunas; other authors conceive the Biharian as 

beginning with the first appearance of a Biharian immigrant 

(Allophaiomys-the first microtine with rootless teeth other 

than the lemmings) and are more influenced by the time of 

immigration than by the overall faunal composition. 

Defining the Biharian Stage as beginning with the earliest immigrant that is characteristic of that stage (Allophaiomys), regardless of the nature of the rest of the fauna, is 

followed in this report. This definition is believed to be a 

more precise time signal than is the gradual change in general faunal composition. In the United States the first Irvingtonian immigrant also is Allophaiomys and also appears at 

the beginning of the Olduvai event (1.9 Ma), but other faunal 

elements have a strong Blancan V (next older age) composition until at least 1.4 million years ago. In addition, the same 

earliest appearance of Allophaiomys occurs in other places 

around the world, apparently close to the same time, so that 

the beginning of this small-mammal stage is easily recognizable in many places by the "oldestAllophaiomys." 

In North America the correlative age boundary, the 

Blancan-Irvingtonian boundary, can be dated either at 1.9 

million years ago, if the first Irvingtonian immigrant (Allophaiomys) is the criterion (Repenning, 1987), or at about 1.4 

million years ago, if the last prominently Blancan faunal 

assemblage is the criterion. The frrst North American record 

of Allophaiomys, at the beginning of the Olduvai event in 

southern Colorado, is remarkably similar in age to that in 

Europe (Holland; van Kolfschoten, 1988). However, 

endemic faunal change in Europe may have progressed 

faster than in the United States, where the Blancan aspect of 

faunas persisted at least 500,000 years after the arrival of 

Allophaiomys. The difference in philosophical concept is of 

little significance, but the difference in use as a correlation 

tool is great and requires a statement of usage to avoid confusion in discussion. 

Allophaiomys may have disappeared before the 

Jaramillo Normal-polarity Subchron in northern Europe. In 

Holland the youngest records of Allophaiomys are approximately late Eburonian in age (van Kolfschoten, 1988). This 

age termination has not been dated more closely than 

between the Olduvai and the Jaramillo events (1.67 to 0.97 

Ma). However, T. van Kolfschoten (written commun., 1991) 

has indicated that Allophaiomys morphotypes have been 

found, with the first appearance of Microtus, in the Bavelian 

fauna of Holland (during the Jaramillo event). These morphotypes of Allophaiomys may (or may not) represent variants in populations of Terricola, as in the Karay-Dubina 

fauna of the Ukraine. Allophaiomys is not often associated 

with Microtus as herein defined, as the two genera represent 

much different stages in evolution as well as different environmental tolerances. 

Because of the habit of listing morpho type variations of 

one population as individuals of a different species and different genera, the youngest record of Allophaiomys in 

Europe is not certainly known, and cannot be used to estimate the age ofBetfia-2. More faunal populations need to be 

evaluated in the manner ofFejfar and Horacek (1983). 

The Karay-Dubina fauna of the Ukraine (Markova, 

1982, 1990) has been cited as a late record of Allophaiomys; 

however, its inferred age is based only upon the base of the 

Brunhes Chron some 8 m (26 ft) higher in the section, and 

the magnetic polarity of the fossil horizon itself is unknown, 

as is its position within the Matuyama Reversed-polarity 

Chron. Figure 6 of Markova (1982) and figure 16 of Markova (1990), in combination with figure 1 of Velichko and 

others (1983), indicate from three to five erosional unconformities in the section between the base of the Brunhes Chron 

and the underlying Karay-Dubina fauna of unknown paleomagnetic polarity. 

In addition, to judge from Markova's (1990) excellent 

illustrations, Terricola hintoni and Allophaiomys pliocaenicus morphotypes intergrade and appear to constitute a single 
GENUS ALLOPHAIOMYS 31 

variable population (of Terricola). Twenty-three specimens 

are illustrated by Markova (1990), of which Terricola 

morphotypes represent 60 percent, intermediate morphotypes represent 14 percent, and Allophaiomys morphotypes 

(lacking any sign of Secondary Wings and having a relatively large Dimension B-B') represent 17 percent of the 

illustrated population sample. 

From published information only, it would appear that 

Allophaiomys should not be recognized in the Karay-Dubina 

fauna and that the entire population should be considered a 

primitive population of Terricola hintoni with individual 

variants overlapping the morphology of Allophaiomys. The 

same logic that would recognize Allophaiomys in the KarayDubina fauna would recognize Allophaiomys in the Trout 

Cave No. 2 fauna of West Virginia (Pfaff, 1990; about 

725,000 years old, to be discussed) and in the living populations of Pedomys ochrogaster. 

In summary, the youngest populations of Allophaiomys 

known from Europe probably are of an age intermediate 

between the ages of the Jaramillo and the Olduvai Normalpolarity Subchrons, approximately of latest Waalian age, 

which is inferred to be about 1.4 million years ago (Repenning and Brouwers, 1992). In the United States, as will be 

discussed, Allophaiomys survived until about 70,000 years 

after the Jaramillo event. Records this young in Europe, 

insofar as they have been presently evaluated, appear to be 

Allophaiomys morphotypes that are variants from populations of more advanced genera, primarily Terricola; in the 

United States such variants are found in populations of 

Pitymys and Pedomys, and include the living Pedomys 

ochrogaster. 

The oldest records in western Europe appear to be at the 

base of the Olduvai event and may be slightly older in the 

Black Sea area, where the oldest Allophaiomys appears to be 

pre-Olduvai. In the People's Republic of China the genus is 

demonstrably this old. By faunal approximation, the type 

locality, Betfia-2, is presumed to be about as old as the end 

of the Olduvai event (fig. 14), or at the Pliocene-Pleistocene 

boundary. 

Allophaiomys pliocaenicus differs from living Phaiomys leucurus in its much greater individual variation, in 

only occasional angularity on the posterolingual portion of 

the Cap, and in enamel differentiation. It differs from its 

derived genera by the lack of closure of Dimension C-C' 

(Lasiopodomys, Lemmiscus, Proedromys, and Microtus), the 

lack of Secondary Wings on the Anteroconid Cap (Pitymys 

and Pedomys), or the lack of either the lingual or both Secondary Wings and closure of Dimension B-B' (Terricola). 

Evolution into derived genera is accomplished primarily by direct drift of morphologic variation into the defined 

morphology of the descendant taxa but can also occur 

through the development of bimodal distribution of dental 

characters, a polymorphism recording two closely related 

taxa in the population sample. Evolutionary extinction 

through linear morphologic drift into a derived taxon 

morphology is accomplished in single, provincial populations and does not occur everywhere at the same time. These 

statements will be illustrated on the following pages. 

North American record.-The record of Allophaiomys 

from North America is very similar to that in Eurasia. It 

begins with nearly typical Allophaiomys that evolved progressive individual variability, overlapping the definitions of 

derived genera that are somewhat different than those in 

Eurasia. In North America Lasiopodomys is an immigrant 

and cannot be traced back to Allophaiomys as it can in 

Eurasia. In addition, Microtus (with one exception) and 

Terricola also appear as immigrants in North America; these 

appear much later than the immigration of Allophaiomys. 

All evidence of evolution out of Allophaiomys in North 

America is toward the endemic genera Lemmiscus, Pitymys, 

and Pedomys. In some faunas these events are well dated. 

The earliest records of both Microtus and Lasiopodomys in 

North America indicate that more and earlier evolution of 

genera out of Allophaiomys is yet to be discovered in Eurasia 

or recognized by better external dating. 

Allophaiomys is known in North America only to the 

east of the Rocky Mountains, although both Lasiopodomys 

and Microtus are known, at different times, both east and 

west of this mountain range. Terricola is also known to the 

west of these mountains, but appears to have arrived there by 

dispersing southward from Beringia down the east side of 

the mountain range, westward around its south end, and then 

northward up the Pacific Coast (Repenning, 1983). 

Provincial differences in degree and direction of individual morphologic variation, as well as of dispersal 

patterns, exist in North America and could confuse age 

interpretations based only on the stage of evolution within 

the genus Allophaiomys as now known. These differences 

suggest that caution be used in inferring the history in Asia 

only from the recorded events of Europe and North America. An extreme example of provincial differences in the 

timing of evolution is discussed later in the section titled 

"Provinciality." 

The oldest record of Allophaiomys in North America 

may be slightly more ancient than that in Holland. This 

record is a single, rootless tooth, a third lower molar (fig. 7), 

recovered from a core drilled at the foot of Hansen Bluff, 

south-central Colorado, in the eastern part of the Rocky 

Mountains. As will be discussed, the foot of Hansen Bluff is 

in reversed deposits of the Matuyama Reversed-polarity 

Chron below the Brunhes Normal-polarity Chron and above 

the Jaramillo Normal .. polarity Subchron (Rogers and others, 

1985). The core passed through the Jaramillo event and continued down through the Olduvai Normal-polarity Subchron 

and bottomed in the Gauss Normal-polarity Chron (Rogers 

and others, 1992). 

At 240 ft (73.1 m) depth in this core, a single microtine 

tooth was recovered (fig. 7 E). The first polarity sample 

upcore from the tooth, at 237ft (72.2 m) depth, was normal 

and represented the lowest record of the Olduvai event; the 
32 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

first polarity sample downcore was reversed and at 241 ft 

(73.4 m) depth. Therefore, the microtine tooth was deposited 

either during the oldest part of the Olduvai event or just 

before it (Rogers and others, 1992); it came from a 4-ft (1.2-

m) section between the polarity determinations. 

The tooth cannot be certainly identified as being that of 

Allophaiomys, but its age and dental pattern make it very difficult to imagine that it represents any other rootless microtine rodent; none but the lemmings had evolved before the 

Olduvai event, and the tooth does not belong to a lemming. 

It could belong to nearly any member of the tribes Microtini 

or Pitymyini, but the existence of these at such an early date 

is unbelievable. Other dated records of Allophaiomys in 

North America are younger than the Olduvai event. 

In North America, the youngest dated record of a population that can be assigned to Allophaiomys is about 

830,000 years old and is of an evolved form that has been 

described as Allophaiomys guildayi (van der Meulen, 1978). 

Allophaiomys morphotypes are known in many younger 

North American faunas including the population of Pedomys 

llanensis from Trout Cave No. 2, West Virginia (perhaps 

725,000 years old; about 34 percent Allophaiomys morphotypes) and the living Pedomys ochrogaster (a very small percentage). These will be discussed in following sections. 

AUOPHAIOMYS FROM THE JAVA FAUNA 

(fig. 5; locality 10, fig. 1) 

The Java fauna, from north-central South Dakota, 

U.S.A. (Martin, 1989), is of early Irvingtonian age. External 

age control has not been established, but the fauna includes 

holdover late Blancan microtines, including Mimomys, 

Pliophenacomys, Guildayomys, and a primitive Ondatra 

(Martin, 1989). Holdover microtines of the Blancan V age 

(Mimomys parvus, Mictomys vetus, and Ondatra idahoensis) are known in older Irvingtonian faunas as young as (or 

younger than) about 1.4 million years ago (Vallecito Creek 

faunal sequence in the Anza-Borrego Desert, California; 

Zakrzewski, 1972; author's unpub. data, 1990). The Java 

fauna also includes the Irvingtonian immigrant microtines 

Phenacomys and Allophaiomys, the earliest records east of 

the Rocky Mountains (exceptAllophaiomys from Colorado). 

Phenacomys frrst appears in Idaho later than the Olduvai 

event, with Blancan holdovers (Froman Ferry faunas, Idaho, 

also containing Mimomys parvus, Mictomys vetus, and 

Ondatra idahoensis; author's unpub. data). Climatic constraints cited by Repenning (1990; it is a very warm and wet 

fauna) seem to indicate that the Java fauna is older than 1.7 

or younger than 1.5 million years because this period of time 

was relatively cool in the Northern Hemisphere (Repenning 

and Brouwers, 1992). Therefore the Java fauna is considered 

as being between 1.9 and 1.4 million years old-during the 

early part of the Irvingtonian I microtine age in the United 

States but probably excluding the time between 1.7 and 1.5 

million years ago (fig. 14). It was deposited either during or 

after the Olduvai event; a magnetic polarity determination 

would greatly help to narrow this possible age range. 

The sample of Allophaiomys from the Java fauna is 

large; Martin (1989) listed well over 100 first lower molars. 

However, the assignment to a species is difficult and 

involves theoretical considerations. Only a small portion of 

the sample (n=9) was examined for this study. The population characteristics are as follows. 

Martin (1989) noted that various dental dimensions and 

ratios do not plot in a bimodal distribution; the population 

does not seem to be diversifying. No individuals of Allophaiomys are known from North America that have "Mimomys" 

enamel-thickness differentiation; about 80 percent of the 

Java fauna sample has "Microtus" enamel-thickness differentiation (about 20 percent intermediate), suggesting 

advancement over typical Allophaiomys pliocaenicus from 

Betfia-2. Some populations of more advancedAllophaiomys 

in North America, such as of Allophaiomys guildayi, have 

only "Microtus" differentiation. 

In the Java sample the range of individual variability 

does not include Pitymys morphotypes, unlike most later 

populations in the United States that overlap the morphology 

of Pitymys or Pedomys, whereas a small percentage of the 

type popu.Iation from Romania is of a Terri cola morphotype. 

Thus the Java sample of Allophaiomys differs from typical 

Allophaiomys pliocaenicus of the Betfia-2 fauna in having 

considerable "Microtus" differentiation of enamel thickness, 

and in having a range of individual variation that does not 

overlap descendant genera (North American). Individuals 

showing these variation modes and extremes are illustrated 

in figure 5. 

The Betfia-2 and Java faunas are on opposite sides of 

the Northern Hemisphere, and the oldest dated record of 

Allophaiomys is in China, suggesting an Asian, possibly east 

Asian, earliest origin of the genus. A reasonable speculation 

is that the European and North American populations belong 

to different, as well as widely separate, lineages of the genus 

and that both may have originated in eastern Asia but developed somewhat different characteristics as they dispersed 

westward to Europe and eastward to the United States. They 

may express somewhat different evolutionary directions, 

although neither is greatly removed from the hypothetical 

common ancestor. The different subsequent vectors of evolution in Europe and North America certainly seem to support this inference. Considerable additional evaluation of 

Asian populations is needed before this suggestion can be 

judged, but one implication is that the specific name pliocaenicus may be inappropriate in North America. The name 

Allophaiomys sp. cf. A. pliocaenicus is here applied to the 

Java population, accordingly. 

As a consequence of this difference in individual variation in the morphotypes of early Allophaiomys, the Java 

fauna cannot be confidently equated by stage of evolution 
GENUS ALLOPHAIOMYS 33 

with the type population from Betfia-2. It is considered as 

only "about" the same age, but, to judge from the broad 

record of evolution of the genus throughout the world, it 

could easily be as much as 100,000 years different in age. 

The Java population appears to have much less individual variability than many of the described Allophaiomys 

populations of Europe. It seems less advanced than the 

Balaruc fauna of France, described by Chaline (1972), and 

certainly less than the Mas Rambault fauna, which appears 

to have more than 50 percent of its individuals with a posterolingual corner on the Cap (Chaline, 1972, fig. 20). Younger 

European faunas have even greater individual morphologic 

variation, for example, the V alerots fauna of France_: 

Surprisingly, both American and French faunas with 

advanced Allophaiomys morphotypes (as described by Chaline, 1972) contain no primitive variants of tribe Microtini 

and do not include morphotypes typical of Lasiopodomys, 

from which Microtus evolved, as will be described. 

Lasiopodomys morphotypes are known from Central Europe 

eastward throughout Asia, and, as immigrants, in North 

America. But apparently the genus Microtus did not evolve 

in France. The same suggestion is evident in Holland where 

Allophaiomys probably became extinct before the immigration of Microtus (van Kolfschoten, 1990). 

Mention has been made of the Allophaiomys/ 

Lasiopodomys transition in the younger Monte Peglia faunas 

of Italy, and other faunas of the Paratethyian region contain 

Allophaiomys variations in Lasiopodomys populations. As 

will be discussed in connection with the microtine fauna of 

Beringia, Allophaiomys and Terricola had (and Terricola 

still has) warmer environmental preferences than did fossil 

Lasiopodomys and Microtus. Thus the first appearance of 

Microtus during the Jaramillo polarity event in France and 

Holland, a date later than farther north or inland in Europe, 

suggests that the North Atlantic Ocean before this time was 

markedly warm, and so was coastal Europe. 

ALLOPHAIOMYS FROM THE SAM CAVE FAUNAS 

(fig. 6; locality 15, fig. 1) 

SAM Cave is in the valley of the Rio Grande in northernmost New Mexico, U.S.A. The cave is at 8,900 ft (2,728 

m) elevation. It contains a number of imbricated as well as 

isolated sedimentary deposits that include at least nine 

localities containing Allophaiomys. Three additional localities are more recent in age, containing Microtus cf. M. montanus of Beringian or Asian source, but no Allophaiomys. 

Only one of these SAM Cave localities has been examined 

in any detail for this discussion; it is called BOT -4, and 62 

first lower molars of Allophaiomys have been recovered (fig. 

6). BOT-4 also contains a primitive form of Lemmiscus, 

Mictomys kilnsasensis, and two rooted teeth questionably 

assigned to Phenacomys sp. The history of the cave is under 

A B c 

D F 

o 

~ 1 2 mm 

Figure 5. Allophaiomys sp. from Java fauna, South Dakota. A, 

B, and C have "intermediate" enamel-thickness differentiation 

(about 20 percent of the fauna sample); D, E, and Fhave "Microtus" enamel-thickness differentiation (about 80 percent of the 

fauna sample). 

study by K.L. Rogers and the cave has not been described in 

publication. 

Preliminary and contradictory paleomagnetic studies of 

the sediments in SAM Cave seem to indicate an older normal 

polarity, a reversed middle part of the deposits, and a 

younger normal section. Allophaiomys appears to be confined to the older and middle deposits. The presence of 

Microtus cf. M. montanus in the younger normal-polarity 

deposits indicates that the later part of the Brunhes Chron is 

represented. Locality BOT -4 lies in the reversely magnetized deposits, thus representing the Matuyama Chron following the Jaramillo event; the advanced state of the 

populations of Allophaiomys in SAM Cave precludes the 

possibility that the oldest normal magnetism might represent 

the Olduvai event. 

Lasiopodomys and Terricola immigrated to the United 

States about 850,000 years ago (Repenning, 1987; this 

report, p. 63), and neither is present in the several localities 

containing Allophaiomys in SAM Cave. As will be discussed 

later, Lasiopodomys is a genus derived fromAllophaiomys in 

the Old World, and is ancestral to Microtus; Terricola 
34 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

represents the immigrant group of the tribe Pitymyini in 

North America (the "quasiater species group" ofRepenning, 

1983) and has been called Pitymys in all reports prior to 

Chaline and others (1988). 

In the nearby (39 mi, 63 km) Hansen Bluff faunal 

sequence of Colorado, also in reversed deposits of the latest 

Matuyama Chron and dated as 820,000 years old (Rogers 

and others, 1985; possibly only 30,000 years younger than 

BOT -4), both immigrant lineages are represented, although 

Lasiopodomys is represented by its derivative Microtus 

paroperarius. The BOT -4 fauna from SAM Cave existed 

before this immigration but also after the Jaramillo event of 

the Matuyama Chron. The possible range in age is before 

850,000 and after 900,000 years ago; an averaged age of 

875,000 years is arbitrarily assigned (fig. 14). 

The population of Allophaiomys from Locality BOT -4 

(actually from all older SAM Cave localities containing 

Allophaiomys) is distinctly different, in several features, 

from the type material from Betfia-2, Romania. Rather than 

having a typical globular Cap on the Anteroconid Complex 

of the first lower molar (figs. 5, 6, and 8), about 83 percent 

of the sample from BOT -4 has a posterolingual angularity, 

or comer, on the Cap (in the position of lingual salient angle 

5 or lingual Secondary Wing or Triangle 7) (fig. 6D). However, 79 percent of the individuals show no suggestion of 

Triangle 6, the buccal Secondary Wing. 

The enamel pattern on 83 percent of the first lower 

molars of Allophaiomys from SAM Cave, New Mexico, is 

more similar to that of living Phaiomys leucurus (fig. 4 and 

fig. 6D) than to that of typical Allophaiomys pliocaenicus, 

but it is immensely more variable than in the living Phaiomys. A similar typical morphologic pattern and population 

variability range are found in Allophaiomys guildayi from 

the Hanover Quarry Fissure of Pennsylvania (fig. 9), and in 

the Cumberland Cave fauna of Maryland (see van der 

Meulen, 1978, figs. 7E, G, and H), both to be discussed. 

These are younger faunas, and, for reasons also to be discussed, it seems probable that the SAM Cave population of 

Allophaiomys became locally extinct before Allophaiomys 

guildayi evolved. In addition, unlike the Allophaiomys from 

SAM Cave, individual variation within populations of Allophaiomys guildayi overlaps, in percentages varying with the 

advancement of the population, the morphology of Pedomys. 

Therefore, the name Allophaiomys guildayi is not used for 

the SAM Cave faunas, and the species is left unnamed. Giving it a name in this synthesis is inappropriate and this action 

is postponed until the SAM Cave faunas are fully described. 

The great individual variation in the morphology of the 

first lower molar of the Allophaiomys population from SAM 

Cave includes individuals with the morphology of Allophaiomys pliocaenicus from Betfia-2 (fig. 6A, B) as well as with 

the morphology of Lemmiscus (usually treated as a subgenus 

of Lagurus in North America; fig. 6F, G, and J}. However, 

typical morphotypes of Allophaiomys represent less than 4 

percent of the sampled population while Lemmiscus 

morphotypes (13 Mil and 4 M\3) comprise 21 percent, and 

the sample is weakly bimodal. The dominant mode is that of 

Allophaiomys with a moderate development of a posterolingual comer on the Cap (fig. 6D). 

Although the sample from Locality BOT -4 of SAM 

Cave suggests that Lemmiscus evolved from the population 

of Allophaiomys ( 45 first lower molars), the Lemmiscus morphotype was noted in the older populations from other 

localities in SAM Cave. As the interpretation of an origin of 

North American Lemmiscus out of North American Allophaiomys would be of considerable significance in classification, no firm conclusions are here drawn, pending 

consideration of the other populations from SAM Cave. 

Current classification derives Lemmiscus from Old World 

lagurines. These are very similar forms but have recognizable differences, such as the lack of cement in the cheek 

teeth. 

The original examination of the BOT -4 samples recognized the Lemmiscus-like morphology of the last upper 

molars, but it was Alexy Tesakov (Moscow), who, in 

reviewing an earlier version of this report, questioned the 

assignment of the first lower molars to a Microtus-like morphotype, and he correctly suggested that they also might be 

Lemmiscus. 

The Lemmiscus sp. morphotypes from BOT -4, SAM 

Cave, appear to differ from the living Lemmiscus curtatus in 

that the confluence between the lingual Primary Wing (T.5) 

and the Cap (Dimension B-B') is usually open and contains 

a moderately wide neck of dentine (fig. 6F; this neck is 

unusually narrow in fig. 6G, which also has a lingual Secondary Wing). The buccal Secondary Wing (T.6) is always 

present and the lingual Secondary wing (T.7) is not always 

present, as in living Lemmiscus curtatus; this development 

of T.6 in preference to T.7 is opposite to the early trends in 

Microtus in which the lingual Secondary Wing (T.7) appears 

first. Enamel differentiation is of the "Microtus" type. The 

SAM Cave localities are unquestionably the oldest record of 

the genus. The next oldest record is from Porcupine Cave, 

Colorado (Bamosky and Rasmussen, 1988), and is believed 

to be about 450,000 years old. Lemmiscus was not reported 

from the Hansen Bluff faunal sequence (Rogers and others, 

1985). 

Bamosky and Rasmussen (1988), based on the history 

of sedimentation in Porcupine Cave, have suggested that the 

following dentinal features of Lemmiscus may be primitive: 

(1) small size, (2) less constriction of Dimension A-A', and 

(3) a broader Cap anterior to Dimension A-A'. This interpretation appears to be confirmed by the condition of Lemmiscus sp. from the older SAM Cave BOT -4 fauna, which has 

(1) smaller average size (mean length M/1=2.43 mm) than 

six of the samples compared by Bamosky and Rasmussen 

(1988; their table 4 ), but not smaller than all samples, (2) less 

constriction of Dimension A-A', and (3) a broad Cap anterior to A-A' (fig. 6G, but not F-in part a result of less 

wear). 
GENUS ALLOPHAIOMYS 

0 

~ 1 2 mm 

Figure 6. Allophaiomys n. sp. (A-E, H, l) and Lemmiscus n. sp. (F, G, and J) from SAM 

Cave, New Mexico: Locality BOT-4. A-C, "intermediate" differentiation (34 percent of the 

sample); D, E, "Microtus" differentiation (66 percent); D, the modal morphotype in the fauna 

(83 percent of the sample), with a posterolingual angularity on the Cap (T. 7); F, G, Lemmiscus n.sp. first lower molar morphotypes. H, Allophaiomys n. sp. M\3 with "simple" morphotype (87 percent);/, Allophaiomys n. sp. M\3 with weakly "complex" morphotype (the most 

complex in the sample; 13 percent); J, Lemmiscus n. sp.last upper molar. A, D, and E have a 

posterolingual angle on Cap (83 percent of sample). Advancement in variability of the Anteroconid Complex of Allophaiomys n. sp., from the condition of typical Allophaiomys pliocaenicus is comparable to that of Allophaiomys nutiensis from Valerots, France, except for 

the Lemmiscus morphotypes. 

35 

About 66 percent of the SAM Cave sample of Allophaiomys has "Microtus" enamel-thickness differentiation, 

also differing from Allophaiomys guildayi, which has this 

type of enamel-thickness differentiation in all individuals. 

Enamel-thickness differentiation appears to have evolved 

independently of other morphologic characters, and is difficult to equate in detail with evolution. 

Last upper molars from the BOT -4 sample of Allophaiomys are of varied morphology (fig. 6H-l); 88 percent are 

"simple" and 12 percent are somewhat advanced and have a 
36 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

rudimentary posterior hook (fig. 61). Eighteen percent of the 

sample of last upper molars have a great elongation of the 

posterior loop and are assigned to the Lemmiscus sp. 

morphotype (fig. 61). Many of these Lemmiscus last upper 

molars have a reduced anterobuccal reentrant (fig. 61) as do 

many individuals of the living Lemmiscus curtatus. 

The SAM Cave, BOT -4 population of Allophaiomys is 

distinctly more advanced than others that have been considered thus far and is considered a separate species. Although 

similar to the species A. guildayi in having a large majority 

of individuals with an angle developed on the posterolingual 

comer of the Cap, the SAM Cave population is not completely converted to "Microtus" enamel-thickness differentiation and shows no overlap of individual characters with the 

genus Pedomys, as do the samples of A. guildayi from Cumberland Cave and Hanover Quarry Fissure. Figure 6E shows 

the closest approach to pitymyinine characters in the examined sample, and it is not very close. 

Indication of a buccal Secondary Wing is totally lacking in the BOT-4 sample except for the few individuals (21 

percent) assigned to the Lemmiscus morphotype; the Lemmiscus variants are clearly not Pitymys by virtue of the closure between the dentine fields of the Primary Wings 

(closure of Dimension C-C', fig. 6F and G). And they are 

not Microtus because the SAM Cave Lemmiscus variants 

show the development of primarily the buccal Secondary 

Wing, whereas Microtus, Pitymys, Pedomys, and Terricola 

show development of the lingual (or both) Secondary Wings 

(figs. 10, 12, and 13). 

The SAM Cave Lemmiscus morphotypes are different 

than those of Microtus. They shortly predate the arrival from 

Beringia of Terricola and Lasiopodomys, perhaps only by 

25,000 years. Microtus, which evolved from immigrant 

Lasiopodomys, and Terricola were present in the same part 

of the Rio Grande basin as SAM Cave 820,000 years ago, as 

indicated by the records from the Hansen Bluff faunas 39 

miles (63 km) to the north and east (Rogers and others, 

1985). Extinction of Allophaiomys, possible modernization 

of Lemmiscus, immigration of Terricola and Lasiopodomys, 

evolution of Microtus out of Lasiopodomys, and climatic 

change to introduce the Nebraskan continental glaciation to 

North America all happened in this Colorado-New Mexico 

basin of the Rio Grande between the time of the BOT -4 

fauna of SAM Cave and the oldest faunas of the Hansen 

Bluff faunal sequence; between an interpolated 875,000 

years and a rather well controlled date of 820,000 years ago. 

This region is in the eastern belt of the Rocky Mountains. 

Surprisingly, no variations in the SAM Cave population 

resemble Lasiopodomys. This was a very common variation 

of advanced Allophaiomys throughout Eurasia, where it preceded the evolution of Lasiopodomys. The genus Lasiopodomys resulted from the great reduction of Dimension 

C--C', separating the two Primary Wings, without the development of Dimension A-A' and Secondary Wings that 

define Microtus and Lemmiscus. 

The Lasiopodomys morphology is completely avoided 

in the individual variability of the BOT -4 population of 

Allophaiomys by the simultaneous development of a closed 

Dimension C-C' and the appearance of a single, buccal Secondary Wing, forming the Lemmiscus morphotype (fig. 6F, 

G). North American Lasiopodomys was an immigrant. 

All available records indicate that the development of a 

lingual Secondary Wing marks the origination of Microtus; 

the Lemmiscus morphotypes of Allophaiomys from the SAM 

Cave do not conform to this pattern. The origins of 

Lasiopodomys and, with one exception, Microtus are in the 

Old World. Also, there is only very slight suggestion of the 

variation that led to the Pitymyini in the SAM Cave population (fig. 6D, E), in which the Secondary Wings alone developed and Dimension C-C' remained unreduced; in the SAM 

Cave sample a few individuals of Allophaiomys have a 

slightly reduced Dimension B-B', suggesting the Pitymyini. 

Greater variation toward the Pitymyini is found in all other 

Allophaiomys populations of the United States soon after the 

SAM Cave fauna lived. Thus the SAM Cave population is 

unique in North America in its direction of variation toward 

the Lemmiscus morphotype, as well as in avoiding an intermediate Lasiopodomys morphotype leading to Microtus or 

significant morphologic gradation toward the Pitymyini. 

The unique individual variation forming the Lemmiscus 

morphotype in Allophaiomys from SAM Cave, New Mexico, emphasizes the fact that different populations of Allophaiomys had different evolutionary patterns. SAM Cave is 

now well south of the range of living Lemmiscus, and this 

distribution and the modem colder summer preferences of 

Lemmiscus curtatus prompt the suggestion that the fauna 

may represent a high elevation (8,900 ft; 2,728 m) province; 

the next younger record, Porcupine Cave, Colorado (Barnosky and Rasmussen, 1988), is higher (9,500 ft; 2,900 m) 

and ·half as old (perhaps 450,000 years old), and lies half as 

far from the modem range of the genus beginning in high 

plains at the northern boundary of Colorado. 

ALLOPHAIOMYS FROM THE WELLSCH VALLEY FAUNA 

(fig. 7; locality 9, fig. 1) 

The Wellsch Valley fauna is in southern Saskatchewan, 

Canada (Churcher, 1984). Although earlier paleomagnetic 

studies indicated deposition during the Olduvai event, recent 

restudy (Barendregt and others, 1991) indicates that the 

Jaramillo and Olduvai normal events are not present in the 

section. The fossil locality was deposited before the 

beginning of the Brunhes Chron in reversely magnetized 

beds of the Matuyama Chron; its position within the 

Matuyama is uncertain, although the faunal horizon is 

reversely magnetized and cannot correlate with the Jaramillo 

event. The age of the fauna may be very close to, or the same 

as, the age of BOT -4 of SAM Cave, New Mexico. 
GENUS AUOPHAIOMYS 37 

The fauna represents a warm climate (Churcher, 1984) 

and cannot be contemporaneous with the Nebraskan glaciation (the locality was indeed covered by this ice sheet): 

therefore it must be older than 850,000 years. This conclusion is also suggested by the absence of both Lasiopodomys 

and Terricola, both of which appear to have entered the 

United States from Beringia at the beginning of Nebraskan 

glaciation. 

The Wellsch Valley fauna contains one Blancan holdover, the canid Boraphagus. An advanced form of Microtus 

is present in the fauna, and the history of Beringian Microtus 

suggests that the fauna is the age of or younger than the 

Jaramillo event; its reversed polarity eliminates the possibility of an equivalent age. Biogeographic considerations suggest that the Wellsch Valley Microtus probably is not as old 

as 1.5 million years; no record is known of this genus that is 

older than this age, and Wellsch Valley is on the east side of 

the Rocky Mountains where there is no record of Microtus 

so old in the United States. 

The sample of Allophaiomys from the Wellsch Valley 

fauna is very small, consisting of only four first lower molars 

(fig. 7); no evaluation of individual variation is possible. 

Three of the four specimens known are of typical morphology, but have "Microtus" enamel-thickness differentiation 

and show a remarkably great size variation (fig. 7). The 

fourth first lower molar is an individual variant with a posterolingual angularity on the Cap, overlapping the morphology of Allophaiomys guildayi and the species from SAM 

Cave. 

The few last upper molars from the Wellsch Valley 

fauna are of a "simple" structure and presumably are assignable to Allophaiomys. The associated first lower molar of 

Microtus is too advanced to be considered as having a simple 

last upper molar. 

In the Wellsch Valley fauna the association ofAllophaiomys with a rather advanced species of Microtus is of great 

interest. The single specimen of Microtus has a first lower 

molar that is morphologically similar to the most advanced 

morphotypes of Microtus paroperarius from its type locality, the 610,000 year-old Cudahy fauna of Kansas. It has a 

fully closed Dimension C-C' (separating the two Primary 

Wings), a fully closed Dimension B-B' (between the lingual 

Primary Wing and the Cap) and well-developed Secondary 

Wings (fig. 7 D, reproduced from a manuscript by C.S. 

Churcher). This is the only association in North America, 

possibly in the world, of Allophaiomys with so advanced a 

Microtus morphotype. 

In the latitudinal confines of the United States east of 

the Rocky Mountains, the presence of a species of Microtus 

with an advanced first lower molar in a late Matuyama fauna 

is unknown. East of the Rocky Mountains, no Microtus is 

known before 830,000 years ago and those that are known 

before the Brunhes have recently evolved out of the immigrant Lasiopodomys. They are primitive and have only very 

weak development of Secondary Wings. It was not until 

B 

0 

~ 1 2 mm 

E 

Figure 7. Allophaiomys sp. and Microtus sp. from the Wellsch 

Valley fauna, Saskatchewan; M/3 from the Hansen Bluff core, 

Colorado. A and B, Allophaiomys sp. first lower molars; note size 

variation. C, Allophaiomys last upper molar. D, Microtus sp., 

NMC 17848-first lower molar, reproduced from a manuscript 

by C. S. Churcher. E, Last lower molar, assigned toAllophaiomys 

on basis of great age and rootless state, from the base of the Olduvai event in Hansen Bluff core, Colorado. NMC specimens 

except for E, which is in Adams State College, Alamosa, 

Colorado. 

about 700,000 years ago, well into the time of the Brunhes 

Normal-polarity Chron, that Microtus paroperarius in the 

United States evolved to the point where some individuals 

were as advanced as the Microtus specimen from the 

Wellsch Valley fauna. Allophaiomys became extinct in the 

United States before this time, but the Wellsch Valley fauna 

is from reversely polarized deposits. 

In addition, in faunas east of the Rocky Mountains in 

the United States, the earliest records of Microtus are associated with Terricola or Lasiopodomys, which immigrated to 

the United States 850,000 years ago. Neither Lasiopodomys 

nor Terricola is known from the Wellsch Valley fauna, suggesting that this Canadian fauna is older than their immigration, and older than the first primitive Microtus of the United 

States east of the Rocky Mountains. 

In Beringia the oldest record of Microtus (Krestovka 

Sections) is of a more primitive morphotype (fig. 16) and 
38 AUOPHAIOMYS AND THE OL YOR SUITE, Y AKUTIA 

predates the Jaramillo event by 200,000 years. In eastern 

Beringia (northwestern Canada) both advanced and primitive Microtus morphotypes were present during the 

Jaramillo Normal-polarity Subchron (fig. 14). Lasiopodomys was associated with these varied Microtus types in 

Beringia, but Allophaiomys was extinct in this region long 

before this time. As will be discussed later in this report, it 

appears that Allophaiomys became extinct in the Arctic 

region during the Olduvai event, probably before 1.7 million 

years ago. Its extinction appears to have been climatically 

regulated, as Allophaiomys was present in Beringia only during an extremely warm period. 

The varied morphotypes of Microtus that lived during 

the Jaramillo event in eastern Beringia are known from 

Locality CRH-47 of the Old Crow basin of northern Yukon 

Territory (R.E. Morlan, oral common., 1986). Two apparently younger faunas from the Old Crow basin also are normally magnetized and contain Lasiopodomys (CRH-11 and 

CRH-64); these have a greater assortment of Microtus morphotypes (Morlan, 1984 ). The Old Crow localities (locality 

25, fig. 1) are about 100 miles (160 km) south of the Arctic 

Ocean. 

A much older Microtus, perhaps 1.4 million years old, 

is known from the Anza-Borrego Desert of southern California, west of the Rocky Mountains (Zakrzewski, 1972; this 

report, fig. 10; locality 21, fig. 1). This record is the oldest 

dated Microtus in the world. The species, Microtus californicus (an advanced living species), is also known from the 

Irvington fauna of central California, which is older than the 

Brunhes Chron-possibly about 870,000 years old. The history of advanced Microtus is much longer west of the Rocky 

Mountains than it is east of them in the United States. 

In addition, one fragmentary specimen of Lasiopodomys exists from the Anza-Borrego Desert of California 

that also predates the Jaramillo event and is about 1.2 million 

years old (fig. 11A); it is much older than the time of its dispersal to the United States east of the Rocky Mountains. 

Because of these age relationships, Microtus califomicus to the west of the Rocky Mountains, as well as the 

species in the Wellsch Valley fauna, must represent immigrants from Beringia; they cannot be related to Microtus 

paroperarius, which evolved out of Lasiopodomys east of 

the Rocky Mountains after the first Nebraskan ice advance 

(850,000 years ago). 

Although apparently never present in the area west of 

the Rocky Mountains and extinct in Beringia long before the 

Jaramillo event, Allophaiomys survived east of the Rocky 

Mountains in the United States until about 830,000 years 

ago, during the early part of the Nebraskan ice advances. The 

Allophaiomys from Wellsch Valley must represent a northward extension of the then-surviving populations in the 

United States. 

Thus the unique association of Allophaiomys with an 

advanced morphotype of Microtus in the Wellsch Valley 

fauna of southern Saskatchewan must have been the result of 

its intermediate latitudinal position between the Beringian 

and the eastern United States faunal regions. At the time that 

this fauna lived, Allophaiomys had been extinct for about 

850,000 years in Beringia but still survived in the United 

States. Microtus was not known to the east of the Rocky 

Mountains in the United States until30,000 years later, and 

even then was of a much less advanced morphology. However, the variety of Microtus morphotypes, some advanced, 

known from Beringia during the earlier Jaramillo event indicates that the Wellsch Valley locality was far enough south 

to support Allophaiomys from the populations still living in 

the United States and far enough north that it included 

Microtus from Beringian populations, where Allophaiomys 

was extinct. 

Based on (1) its reversed polarity (>790,000 years old 

and not Jaramillo); (2) the presence of an advanced Microtus 

morphotype (not related to Microtus of the U.S.A., which 

evolved later and did not develop an advanced morphology 

before the Brunhes Chron, 790,000 years ago); (3) the presence of Allophaiomys (extinct to the south in the Great Plains 

before the Brunhes Chron and apparently extinct to the north 

in Beringia during the Olduvai Subchron); (4) the lack of 

both Lasiopodomys and Terricola (immigrants to the Great 

Plains to the south about 850,000 years ago); (5) the lack of 

abundant Blancan holdovers (less than 1.4 Ma); and (6) 

based on evidence of a warm climate, older than the first 

Nebraskan glacial advance 850,000 years ago, the Wellsch 

Valley fauna is here presumed to be between 850,000 and 

900,000 years old. Some possibility remains that the 

Jaramillo event, missing in the Wellsch Valley polarity section, is younger than the fauna and that the fauna may be 

between 1.0 and 1.4 million years old (fig. 14). One Californian locality (Anza Borrego) contains an advanced Microtus 

that is this old, but this form appears less advanced and is 

associated with many Blancan holdovers. 

AILOPHAIOMYS FROM THE CHEETAH ROOM FAUNA 

(fig. 8;-locality 17, fig. 1) 

The Cheetah Room fauna is from Hamilton Cave, West 

Virginia, and contains a large variety of microtine rodents. 

These include a population of the southern bog lemming 

Synaptomys cooperi with a remarkable individual variation 

overlapping that of the northern bog lemming Mictomys 

borealis, a primitive subgenus of Phenacomys, and a very 

late record of the genus Mimomys of the tribe Arvicolini, as 

well as Allophaiomys, Lasiopodomys, and Pitymys. In the 

original description of the Cheetah Room fauna (Repenning 

and Grady, 1988), Microtus paroperarius was also listed, 

but this identification was based upon a minority of extreme 

variants in the population of Lasiopodomys deceitensis and 

not upon a bimodal distribution of morphotypes; the identification is here withdrawn, although the specimens are very 

primitive Microtus morphotypes. 
GENUS AUOPHAIOMYS 39 

No external control of the age of the Cheetah Room 

fauna exists, but overlapping biochronologies identify its 

age closely. Based upon the emergence of the southern bog 

lemming Synaptomys out of the northern bog lemming 

Mictomys in the Cheetah Room fauna, the fauna is older than 

the Brunhes Normal-polarity Chron (beginning about 

790,000 years ago); Synaptomys is known elsewhere before 

the Brunhes. Based upon the presence of the immigrant 

genus Lasiopodomys, the Cheetah Room fauna is younger 

than the dispersal event that introduced Irvingtonian II 

microtine rodents to the faunas of the United States (about 

850,000 years ago; Repenning, 1987; Repenning and others, 

1990). The presence of Lasiopodomys indicates that the 

Cheetah Room fauna is older than the oldest faunas of the 

Hansen Bluff faunal sequence in Colorado (820,000 years 

old; Rogers and others, 1985), which contain immigrant, 

primitive Terricola and Microtus paroperarius, but not 

immigrant Lasiopodomys, from which Microtus evolved, as 

will be discussed. 

The Cheetah Room fauna is thus older than 820,000 

years and younger than 850,000 years. Other faunas, to be 

discussed, are also of this age range but younger than the 

Cheetah Room fauna, making it seem that the Cheetah Room 

fauna must be closer to 850,000 than to 820,000 years old; it 

is considered to be about 840,000 years old (fig. 14). 

Although additional material is available at USNM, the 

examined sample of Allophaiomys from the Cheetah Room 

fauna comprises 30 first lower molars. Separation of the 

immigrant genus Lasiopodomys fromAllophaiomys presents 

no problem, but the gradation between Allophaiomys and 

Pitymys (representing the native "pinetorum species group" 

of Repenning, 1983) is complete and distinctly bimodal. 

Fifty-two first lower molars assigned to Pitymys hibbardi are in the examined sample, and individual variation 

not only overlaps that of Allophaiomys but also overlaps the 

typical morphology of Pitymys cumberlandensis ("intermediate" enamel differentiation) and the type species of the 

genus, Pitymys pinetorum (fig. 13A, B, and C; see also 

Repenning and Grady, 1988). It had been suggested in earlier publications that North American Pitymys evolved provincially out of endemic Allophaiomys (van der Meulen, 

1978; Repenning, 1983). 

The 30 first lower molars of Allophaiomys from the 

Cheetah Room fauna (exemplified in fig. 8) differ considerably from the sample from SAM Cave (fig. 6). Although the 

great majority (83 percent) of first lower molars from SAM 

Cave show a posterolingual angularity on the Cap, only 10 

percent of the Allophaiomys from the Cheetah Room fauna 

can be considered as possibly showing this character, and in 

these individuals the suggestion is weak. 

In addition, in the Cheetah Room sample the configuration of the last upper molar is like that of the type population: 

the sample lacks a substantial percentage of individuals with 

a greatly extended (Lagurus-like) posterior loop and lacks 

any suggestion of the development of a posterior hook. The 

Lemmiscus morphotypes present in the sample from SAM 

Cave are completely lacking in the Cheetah Room fauna. 

Individual variation in the morphology of the frrst lower 

molar does not overlap that of either Lemmiscus or Microtus, 

but grades into that of Pitymys. The distribution of Allophaiomys and Pitymys morphologies is distinctly bimodal in the 

Cheetah Room sample. 

Clearly, the first lower molars and the last upper molars 

of Allophaiomys from the Cheetah Room fauna are more 

similar to teeth of the type population of Allophaiomys from 

Betfia-2 (fig. 3) than to these teeth in the SAM Cave fauna 

of New Mexico. However, enamel-thickness differentiation 

is not greatly different from that of SAM Cave and, as in that 

sample, "Microtus" differentiation is present in half the individuals from the Cheetah Room fauna. This approximate 

proportion of "Microtus" differentiation is equal in both 

Allophaiomys and Pitymys modes of this bimodal population. The Pitymys mode is referred to Pitymys hibbardi 

(Repenning and Grady, 1988). 

Although younger than the SAM Cave population, that 

from the Cheetah Room fauna is not considered to be a new 

species, but an advanced condition of Allophaiomys sp. cf. A. 

pliocaenicus frrst seen in the Java fauna. It is not so advanced 

in the modal morphology of the Allophaiomys part of the 

population as is Allophaiomys guildayi. Its apparently more 

"conventional" morphology also suggests that the older 

SAM Cave population, overlapping the Lemmiscus morphology, was an isolate population, some characters of 

which parallel those seen in Allophaiomys guildayi. 

The Cheetah Room population of Allophaiomys grades 

into the morphology of Pitymys, and the bimodal population 

has a much higher percentage of pitymyinine morphotypes 

than the type population of Allophaiomys pliocaenicus 

(Betfia-2). The differences in the population structure 

between SAM Cave and the Cheetah Room suggest not only 

separate lineages but also a more advanced condition toward 

a descendant generic group in the Cheetah Room population. 

A separate species name would seem justifiable, but is 

neither applied nor endorsed here. Conceivably, one could 

apply a new name to every population in this rapidly 

evolving lineage to the disadvantage of comprehensible 

nomenclature. 

It seems best, in the present state of knowledge, to 

advocate the application of whatever specific name is 

applied to the Java form with the notation that the Cheetah 

Room population is the same but much more advanced. 

Hence, "Allophaiomys sp. cf. A. pliocaenicus, advanced" is 

used in the present report. The population is, however, bimodal and thus must further be described as "Allophaiomys sp. 

cf. A. pliocaenicus-Pitymys hibbardi," which far exceeds the 

usual length of a binomial and is quite cumbersome. The 

sooner that a new name is applied to the Java fauna form of 

Allophaiomys the better. The Cheetah Room species is 

replaced, in perhaps 5,000 years, by a new name, 

Allophaiomys guildayi from the Hanover Quarry Fissure 
40 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

G 

I 0 1 2 mm 

Figure 8. Allophaiomys sp. cf. A. pliocaenicus (advanced): first lower molars from the Cheetah 

Room fauna, Hamilton Cave, West Virginia. A-E, intermediate enamel differentiation. F-H, 

"Microtus" enamel differentiation. /, J, little-worn teeth showing that differentiation is not obvious 

with little wear. K, simple M\3 with long posterior loop. L, simple M\3 with short posterior loop. 

USNM specimens. 

fauna, so the snowballing of qualifiers ends here, and begins 

again. 

The differences in Allophaiomys tooth morphology 

variation between the SAM Cave fauna of New Mexico and 

the slightly younger Cheetah Room fauna of West Virginia, 

faunas that are possibly less than 35,000 years different in 

age, suggest that provincialism may have a significant effect 

on population morphology. Certainly, the total population 

from SAM Cave is more derived in terms of character 

changes than that from the Cheetah Room fauna. It also 

seems evident that the SAM cave form is evolving into 

Lemmiscus whereas the Cheetah Room form has branched a 

new genus called Pitymys. Lacking other age control, this 

could have been interpreted as an age-significant difference, 
GENUS ALLOPHAIOMYS 41 

in a sense that is opposite to that evident from the rest of the 

fauna: the more "derived" Allophaiomys from SAM Cave is 

older than that from the Cheetah Room fauna on several 

counts. 

AI.LOPHAIOMYS FROM THE HANOVER QUARRY 

FISSURE FAUNA 

(fig. 9; locality 16, fig. 1) 

The Hanover Quarry Fissure locality was exposed in 

Bethlehem Steel Corporation's limestone quarry at Hanover, 

Pennsylvania. The fauna contains Allophaiomys guildayi 

(fig. 9), ?Lasiopodomys sp. (fig. 11), and Pitymys cumberlandensis (fig. 13). The original designations by Guilday and 

others (1984) were Pedomys guildayi, Microtus paroperarius, and Pitymys cumberlandensis. The locality does not 

seem to contain a mixed fauna. 

Allophaiomys guildayi is clearly advanced over the type 

species, A. pliocaenicus; the sample is of good size, consisting of 44 first lower molars. In the prevalence (64 percent) 

of an angular posterolingual comer of the Cap (incipient 

lingual Secondary Wing), A. guildayi from the Hanover 

Quarry is similar to the older population of Allophaiomys n. 

sp. from SAM Cave (83 percent with a posterolingual 

comer) and to the apparently younger type population of A. 

guildayi from Cumberland Cave (32 percent; van der 

Meulen, 1978, fig. 7E, G, and possibly H). None of the 

Hanover Quarry sample overlaps the characters of the 

Microtini (Lemmiscus) as does a small percentage (21 percent) of the SAM Cave sample. 

In that only a minor number of individuals (7 percent) 

have developed both Secondary Wings, the Hanover Quarry 

sample is less advanced than the type sample from Cumberland Cave (16 percent). This development (of both Secondary Wings) overlaps the characters of Pedomys, thus 

accounting for the original assignment of the type sample to 

Pedomys guildayi by van der Meulen (1978). However, in 

his type description, van der Meulen stated that the species 

fit the definition of Allophaiomys, and Repenning (1983) 

placed it in this genus, followed by Martin ( 1987) and Pfaff 

(1990). 

In the more advanced population from Trout Cave 

No.2, West Virginia, the Pedomys morphotype represents 

66 percent of the sample, and Pfaff (1990) logically 

assigned the population to Pedomys llanensis, even 

though a minor percentage of the population still retained 

a typical Allophaiomys morphotype (Pfaff, 1990, fig. 5C, 

D, and E). 

Pedomys llanensis was defined by Hibbard (1944) 

from the Cudahy fauna of Kansas, and at most five topotypic specimens have been mentioned in publication. The 

sample is much too small to establish individual variation of 

the type population, and Pfaffs (1990) referral of the Trout 

Cave No. 2 population to this species thus provides proxy 

population characteristics by reference. 

Although van der Meulen (1978) recognized the gradation from Allophaiomys to Pedomys in the Cumberland 

Cave fauna, the addition of the faunas from Hanover 

Quarry and from Trout Cave provides a sequence of populations with increasing percentages of Pedomys morphotypes leading, from Allophaiomys guildayi, through 

Pedomys llanensis, to the living Pedomys ochrogaster. This 

sequence with the increasing proportions of the Pedomys 

morphotypes in evolving populations of advanced Allophaiomys (Hanover-7 percent, Cumberland Cave-16 percent, 

and Trout Cave-66 percent) is here considered as strong 

evidence of age relationship. Martin (1987) mentioned that 

some individuals of living Pedomys ochrogaster still have 

an Allophaiomys dental morphology, although they must 

represent a very small percentage of the population. 

Other aspects of the Allophaiomys population from 

Cumberland Cave, however, as well as features of the Cumberland Cave population of Microtus, are not in complete 

agreement with this interpretation of an evolutionary 

sequence. These other aspects are discussed in later sections. 

The Hanover Quarry Fissure fauna is considered 

younger than the SAM Cave fauna because of this variation 

in Allophaiomys that overlaps the Pitymyini rather than a 

lineage of the Microtini (Lemmiscus) in SAM Cave, and 

because of the presence of the immigrant lineage represented 

by ?Lasiopodomys that is not present in the SAM Cave 

faunas. All specimens of Allophaiomys guildayi from the 

Hanover Quarry Fissure have "Microtus" enamel differentiation, further suggestion of advancement beyond the species 

from SAM Cave and, also, beyond the species of Allophaiomys from the Cheetah Room fauna. 

The sample of Pitymys cumberlandensis from Hanover 

Quarry appears to be the same as in the type locality, Cumberland Cave, Maryland. It is represented by 21 first lower 

molars, of which 86 percent have "intermediate" enamelthickness differentiation; but otherwise this population 

sample is very similar to the living Pitymys pinetorum, 

which has "Microtus" enamel-thickness differentiation in 

most(?) of its population. Pitymys cumberlandensis evolved 

out of Allophaiomys earlier, the process being recorded in 

the Cheetah Room fauna. 

The lack of difference between Pitymys cumberlandensis of the Hanover Quarry population and that of the Cumberland Cave fauna is continued into the younger Trout Cave 

No.2 fauna (Pfaff, 1990) and strongly suggests that this lineage had polarized its morphologic variation after diverging 

from Allophaiomys in the Cheetah Room fauna. 

It is assumed, from their strong similarity, that this species leads to the living Pitymys pinetorum, but to 1992 no 

fauna has been described in which variability in enamelthickness differentiation increases, leading to the dominant 

"Microtus" differentiation of the living species. This is the 

principal difference between the species, and the increase in 

variability of the enamel-thickness differentiation may be 

recorded only in the living populations. There is no reason to 
42 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

0 1 2mm 

Figure 9. Allophaiomys guildayi from Hanover Quarry Fissure fauna, Pennsylvania. First lower molars. All have 

"Microtus" enamel-thickness differentiation. B, no posterobuccal angle, or corner, on Cap (29 percent; this morphotype is 

comparable to living Phaiomys leucurus). A, C, D, posterobuccal angle on Cap (64 percent). E, F, individuals overlapping 

Pedomys morphotype (7 percent). CMNH specimens. 

think that these variations, characterizing progressing evolution, should not be found in the living fauna. 

ALLOPHAIOMYS FROM THE CUMBERLAND CAVE FAUNA 

(locality 11, fig. 1; illustrated in van der Meulen, 1978) 

Cumberland Cave was exposed during excavation for a 

railway cut in nearly vertical Paleozoic limestone at the 

south side of the town of Corriganville, 4 miles (6.4 km) 

northwest of Cumberland, western Maryland. Study of the 

vertebrate fossils from the cave was begun in 1912 (Gidley 

and Gazin, 1938) and has continued intermittently since 

then, the most recent detailed work being that of van der 

Meulen (1978). The fauna contains a good variety of microtine rodents including Allophaiomys guildayi, Pitymys cumberlandensis, and the most primitive known population of 

Microtus paroperarius, which, because of its very primitive 

condition, is herein referred to as Microtus paroperariusLasiopodomys deceitensis, as has been mentioned and will 

be further discussed. 

The Cumberland Cave population of Allophaiomys 

guildayi, the type population, is represented by a good 

sample of 37 frrst lower molars (available for this study; 
GENUS ALLOPHAIOMYS 43 

van der Meulen cited 200 in his complete study). Of these, 

51 percent have a typical Allophaiomys morpho type (van 

der Meulen, 1978, fig. 7A to D, and F; compared to 29 percent in the Hanover Quarry sample), 32 percent have an 

advanced Allophaiomys morphotype in which a posterolingual comer is evident on the Cap (van der Meulen, 1978, 

fig. 7E, G, and H; compared to 64 percent in the Hanover 

Quarry sample), and 16 percent have a Pedomys morphotype with weak but evident Secondary Wings on both sides 

of the Cap (van der Meulen, 1978, fig. 7I; compared to 7 

percent in the Hanover Quarry sample). 

In other faunas, a higher percentage of primitive morphotypes seems to correlate with older faunas (and a higher 

percentage of advanced morphotypes seems to correlate with 

younger faunas), and the increase in individuals with a 

Pedomys morphotype would seem to correlate with a 

younger fauna. But .the percentages of Allophaiomys morphotypes from Cumberland Cave, just cited, do not seem to 

agree with the increase in Pedomys morphotypes. 

Both localities~umberland Cave and Hanover 

Quarry-have been described in such a way that contamination from unknown faunas by stream action appears unlikely 

to have biased the samples. Guilday and others (1984) specifically stated this unlikelihood at the Hanover Quarry 

Fissure. Gidley's (1913) preliminary report on the Cumberland Cave fauna indicates that although there may have been 

other entrances to Cumberland Cave in the past, they would 

all have been near the crest of a prominent ridge, and introduced sand or gravel in the fossil deposit was almost totally 

lacking. The main entrance to Cumberland Cave appears to 

have been destroyed in digging the railway cut. The differences so far considered between this fauna and that of the 

Hanover Quarry Fissure may relate to unknown environmental differences. Possibly the concept of a suitable 

sample size used herein is too small. In addition, no information is available regarding how the Cumberland Cave 

sample of 37 Mils of Allophaiomys guildayi that was available for this study was selected from the 200 that van der 

Meulen indicated was the total sample. 

As will be discussed, the greater-than-50-percent proportion of Microtus morphotypes in the Cumberland Cave 

population of intergrading Microtus and Lasiopodomys also 

suggests a fauna younger than the Hanover Quarry Fissure 

fauna, although in this case the Hanover sample is very 

small. However, the suggestion is in agreement with the 

greater percentage of Pedomys morphotypes, and this age 

inference is adopted here. In either case, the Hanover Quarry 

and Cumberland Cave faunas appear close in age. 

As has been discussed, the Cumberland Cave fauna 

contains Pitymys cumberlandensis, whose origin out of Allophaiomys appears to be recorded in the Cheetah Room fauna 

of Hamilton Cave, West Virginia, that is estimated to be 

about 840,000 years old. The population of Microtus paroperarius from Cumberland Cave, intergrading with abundant 

Lasiopodomys deceitensis morphotypes, is much more 

advanced than the Lasiopodomys population of the Cheetah 

Room fauna, containing at most 25 percent individual variants of the Microtus morphotype. In addition, the origin of 

Synaptomys out of Mictomys is recorded in the Cheetah 

Room fauna, and both of these lemmings are present in the 

Cumberland Cave fauna with no reported morphologic 

intergradation. Thus, the Cumberland Cave fauna appears to 

be younger than the Cheetah Room fauna. 

The presence of primitive Microtus paroperarius (morphologically comparable to 59 percent of the individuals of 

the Microtus-Lasiopodomys population from Cumberland 

Cave) in the oldest Hansen Bluff faunas, Colorado, without 

any associated Lasiopodomys morphotypes ( 41 percent of 

the Cumberland Cave population) indicates that the Cumberland Cave fauna is older than the oldest Hansen Bluff faunas 

(820,000 years old). The age of the Cumberland Cave fauna 

is consequently approximated at 830,000 years (fig. 14). 

This age is very similar to that which was suggested by van 

der Meulen (1978, fig. 14). 

OTHER NORm AMERICAN LOCALITIES 

Other faunas containing Allophaiomys in North America add little more to the history of the North American evolution of this genus. In the Great Plains region these include 

the Wathena, Kentuck, Nash, Courtland Canal, and Aries 

faunas of Kansas, and the Sappa fauna of Nebraska (Zakrzewski, 1985). These faunas are of an age between those of the 

Java and Cheetah Room faunas but are otherwise not dated 

(the Sappa fauna underlies, by some distance, the Sappa Ash 

dated at 1.2 Ma). The samples of Allophaiomys from these 

faunas show a comparable variability and similarity to the 

Java Allophaiomys sp. cf. A. pliocaenicus. Most were originally described as Pedomys llanensis, but Martin (1975) 

called attention to their similarity to Allophaiomys pliocaenicus. When Chaline (1966) first described the evolution of 

Allophaiomys into Microtus and Pitymys, no one was aware 

that Allophaiomys had existed in North America for over a 

million years. 

Allophaiomys appears to have become "extinct" in the 

United States about 825,000 years ago (between Cumberland Cave and Trout Cave No.2 faunas), by evolving a mode 

in its individual dental morphology that is characteristic of 

living Pedomys ochrogaster. The latest appearance of Allophaiomys morphotypes may be individual variants of P. 

llanensis in the Trout Cave No. 2 fauna of West Virginia 

(Pfaff, 1990); or occasional variants of living P. ochrogaster. In addition to pointing out its close relationship with 

A. guildayi, Pfaff also suggested that P. llanensis may be 

synonymous with ochrogaster-this was not a contradiction, but an expression of close similarity and of a difference 

between the species of Pedomys that expresses, primarily, 

differences in the range of individual variability. 

The lineage of Pitymys pinetorum appears to have 

evolved its characteristic mode slightly earlier, beginning in 
44 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

a bimodal association with Allophaiomys in the Cheetah 

Room fauna, continuing with the polarized morphology of 

Pitymys cumberlandensis in several faunas, and apparently 

culminating in the living species by increasing the predominance of "Microtus" enamel-thickness differentiation. 

Pfaff (1990), in an otherwise very specific report on 

Trout Cave No.2, West Virginia, was rather vague about the 

separation between Pitymys cumberlandensis and living P. 

pinetorum. He suggested that the fossil species appears less 

variable than the living on the basis of examination of specimens of the living species from the central Appalachian 

Mountains. This seems reasonable, and only increasing variability marks the evolution of the living species. This would 

be a trend that was duplicated in the past by Allophaiomys 

pliocaenicus prior to diversification into Lasiopodomys, 

Lemmiscus, Terricola, Pitymys, and Pedomys, and by 

Lasiopodomys prior to evolution into Microtus. In a real 

sense, present evidence seems to indicate that the type species of Pitymys is only now evolving out of P. cumberlandensis, an ancestor with more strongly polarized dental 

characters than its living descendant. 

With the exception of SAM Cave, New Mexico, the 

individual variations of Allophaiomys in North America are 

in the direction of Pitymys and Pedomys. The ancestry of 

native Microtus in the eastern half of the United States lies 

not in immigrant Allophaiomys, but in immigrant Lasiopodomys. Three hundred eighty thousand years later, native 

Microtus was replaced by immigrant Microtus from Beringia and Asia. The presence of this Asian-Beringian population to the north is indicated by two localities in California, 

one possibly 1.4 million years old and the other probably 

about 850,000 years old; by Locality CRH-47 of Yukon Territory about 900,000 years old; by the Wellsch Valley fauna 

of Saskatchewan older than 850,000 years; and in the wave 

of immigration of Beringian Microtus to the United States 

about 450,000 years ago (Repenning, 1987). 

TRIBE MICRariNI. SIMPSON. 1945 

Basis of diagnosis.-Hinton, 1923 (for genus Microtus): "M1 with posterior loop followed by five (or four) substantially closed and alternating triangles and terminated by 

an anterior loop of variable form." 

Revised dental diagnosis.-Genera of the tribe Microtim (subfamily Arvicolinae) lack dentinal confluence 

between the Primary Wings of the Anteroconid Complex 

(Dimension C-C' substantially closed); Cap of the Anteroconid Complex simple or complex (Secondary Wings may 

be present); cheek teeth are rootless with cementum in the 

reentrants. 

Generic contents of the tribe.-Lasiopodomys, Lemmiscus, Microtus, and Proedromys. (Many more genera 

seem potentially recognizable, but are here retained as subgenera of Microtus for lack of data to defend their removal.) 

Discussion.-In the tribe Microtini, Dimension C-C', 

between the Primary Wings of the first lower molar (fig. 1 0), 

is greatly shortened and separates (or nearly separates) the 

two Primary Wings; the buccal wing forms Triangle 4. 

Dimension B-B' may remain the same as inAllophaiomys or 

may be greatly shortened, closing the dentinal confluence 

between the lingual Primary Wing and the Cap, thus forming 

Triangle 5. Dimension A-A' may equal the width of the Cap 

(no sign of Secondary Wings) or be greatly reduced, creating 

a lingual or both Secondary Wings. M\3 is simple or complex, but is complex in the majority of living species. 

Note that the above diagnosis is simplified and not universally accepted. If Dimension C-C' can be shortened in an 

Allophaiomys morphotype to produce a member of the tribe 

Microtini, there seems to be no reason why this dimension 

could not also be shortened in a member of the tribe Pitymyini more derived than Allophaiomys, thus producing a 

species of the Microtini from a species of the Pitymyini. This 

is not evident in the North American record, and thus may be 

not fully appreciated by the author. 

Chaline (1972, p. 300) was possibly the first to defend 

such a suggestion with illustrations, and he implicated the 

gregalis, agrestris, and arvalis groups of Microtus in an origin out of more ancient species of Terricola (his Pitymys), 

such as T. hintoni. He provided no population data. It is the 

present author's impression that such concepts are based on 

very small samples and upon the configuration of the Cap of 

the Anteroconid Complex, the most variable part of the first 

lower molar. However, the present author has not had opportunity to review the pertinent faunas, and Chaline's opinion 

still persists among many authorities, particularly regarding 

the gregalis group (subgenus Stenocranius). 

"Mimomys" enamel-thickness differentiation is very 

rare (but see fig. 16A), intermediate differentiation is 

usual in many fossil forms, and all living species have 

"Microtus" enamel differentiation, with the exception of 

Figure 10 (facing page). Microtus and Terricola with illustrations of dental terms. A, Microtus californicus (LACM 24540 

from Locality LACM 6683) and B, Terricola meadensis (LACM 

24828 from Locality LACM 68123), first lower molars from the 

Anza-Borrego Desert of California. C, Microtus californicus 

(UCMP 71258), first lower and second and last (third) upper 

molars (UCMP 71257) from the Irvington fauna, California 

(Locality UCMP V-3604). Second upper molar (center) shows 

incipient additional posterior dentine field typical of the species. 

Note that the Secondary Wings on the first lower molars of M. 

califomicus are confluent; this has led some to place these specimens in the genus Pitymys; the Primary Wings are, however, 

separated by a closed Dimension C-C' and the specimens conform to the morphology of Microtus. Explanation of dental morphologic terms used throughout text: T., triangle; BRA, buccal 

reentrant angle; LRA, lingual reentrant angle. Anterior is up; posterior is down. Lingual is to left in left-hand drawings, to right in 

right-hand drawings and C. Posterior loops extend lingually. 
DIMENSIONS 

A-A' 

B-B' 

c-c· 

~(/) <tw ma 

wz 

Wet 

cc- :tee 

1-1-

CAP 

SECONDARY 

WINGS 

PRIMARY WINGS 

A 

0 

TRIBE MICROTINI 

>< 

w 

...J 

D. 

:E 

0 

0 

c 

z 

0 

g 

cc 

w 

1-

z 

<t 

POSTERIOR 

LOOP 

c 

1 

T.3 

T.1 

B 

2mm 

ANTERIOR 

LOOP 

CENTRAL 

TRIANGLES 

45 

POSTERIOR 

LOOP 
46 AUOPHAIOMYS AND THE OL YOR SUITE, Y AKUTIA 

Microtus xanthognathus that usually has intermediate 

differentiation. Martin (1987) has noted that the poorly 

known Central American M. oaxacensis also has intermediate enamel-thickness differentiation and that Herpetomys guatemalensis and Orithriomys umbrosus have 

"Mimomys" differentiation. 

Those North American faunas containingAllophaiomys 

that are younger than 850,000 years show varying degrees of 

morphologic shift away from typical A. pliocaenicus and 

toward living North American Pitymys and Pedomys. In 

none of these is there a morphologic overlap in individual 

variability between Allophaiomys and Microtus. In North 

American faunas that are older than 850,000 years, a direction of variation toward the Microtini is known only from 

SAM Cave, New Mexico; this is the unique population with 

a trend of Allophaiomys toward the North American microtine genus Lemmiscus. Otherwise, the origins of the tribe 

Microtini are in the Old World. 

The genus Lasiopodomys has been used for more than 

10 years by the author to indicate an evolutionary grade 

between Allophaiomys and Microtus. This usage was first 

made by Repenning in 1978, was defined by Repenning in 

1983, defined in more detail by Repenning and Grady 

(1988), and is restated in the present report. The concept of 

what should be called Microtus is the same for the present 

author and V.S. Zazhigin (who placed Lasiopodomys in 

Allophaiomys), but their usage is more restricted than that of 

many authors, including Markova (1990), who include 

Lasiopodomys in Microtus. As discussed in the preceding 

section, "Classification," the majority of current students of 

microtine rodents would place all genera discussed in the 

present report in the genus Microtus. 

The less specifically varied and more provincial genera 

Proedromys and Lemmiscus are also mentioned under the 

tribe Microtini. 

GENUS LASIOPODOMYS LATASTE, 1887 

(fig. 11) 

Type species.-Arvicola brandtii Radde, 1861. 

Type locality.-Northeast Mongolia, P.R.C.; locality 

30, in fig. 1. 

Revised dental diagnosis.-A genus of the tribe Microtim with no development of Secondary Wings or of Dimension A-A' on the Cap of the Anteroconid Complex of the 

first lower molar, except in living and some fossil forms of 

the Oriental faunal region, and having a simple last upper 

molar (see discussion). 

"1YPICAL" LASIOPODOMYS 

Revised dental diagnosis.-As for the genus. 

Selection of "typical" morphology.-As defined in the 

living and fossil fauna of the Oriental faunal region (Transbaikalia, Mongolia, and the People's Republic of China with 

minor extensions following topography through the Himalaya), Lasiopodomys is a genus of the tribe Microtini with a 

Dimension B-B' on its first lower molar that is reduced to 

the point of closure at the confluence between Triangle 5 and 

the Cap. It also has slight to moderate reduction of Dimension A-A', forming a weak Secondary Wing or Wings (fig. 

liN, 0). These conditions describe the most advanced morphology of the first lower molar in the genus and this morphology is known only in the Oriental faunal region. 

Universally, the genus has a simple last upper molar. 

As Lasiopodomys is known in the fossil record of the 

rest of the Northern Hemisphere (fig. 11), Dimension B-B' 

usually is wide or only moderately constricted, Triangle 5 is 

not fully formed and is confluent with the Cap, and Dimension A-A' is not evident although a posterolingual angularity 

may appear on the Cap. One exception is noted herein of a 

very advanced form from the Hanover Quarry Fissure fauna 

ofPennsylvania (fig. IlL, M). 

In the Oriental region, Lasiopodomys brandtioides is 

known from mammal zone VI ofZheng and Li (1990; Gongwangling age), which is close to being the oldest record for 

the genus (mid-Matuyama age; :::1.3 Ma); and it is more 

advanced than the specimens from the Hanover Quarry Fissure fauna (:::0.83 Ma). The oldest record for the genus, 

Lasiopodomys praebrandtii from the Kudun fauna ofBuryat 

south of Lake Baikal, is of the more simple and primitive 

form (see Repenning and Grady, 1988, fig. 4B) and is similar 

in structure to the specimens of figure llB-G; the individual 

variation of this species overlaps the morphology of Allophaiomys (Erbaeva, 1976). The fauna is believed to be about 

the age of the Olduvai event on faunal grounds (Repenning 

and others, 1990). Buryat is in western Transbaikalia, the 

north westernmost part of the Oriental faunal region as herein 

defined. 

In all areas other than the Oriental faunal region, the 

appearance of dimension A-A' on the Cap of the first lower 

molar marks the morphologic beginning of Microtus, and 

this condition appears before the last upper molar becomes 

complex, as indicated by one associated upper and lower 

dentition from the oldest faunas of the Hansen Bluff faunal 

sequence in Colorado (fig. 12A), or as indicated by several 

living species of Microtus. The last upper molar is simple in 

living and fossil forms of Lasiopodomys. As a generalization, typical Lasiopodomys, known from abundant fossil 

records throughout the Northern Hemisphere, differs from 

Allophaiomys only by the closure of Dimension C-C'. Some 

workers have assigned such fossils to either Allophaiomys or 

to Microtus, as has been noted. This different usage has 

caused many erroneous biochronologic correlations, as has 

also been noted. 
GENUS IASIOPODOMYS 47 

Thus we have the somewhat awkward situation in 

which the living species of the genus are very advanced 

forms living only in the Oriental faunal region. Most of the 

fossil species in this region are similarly advanced. El~ewhere, from Maryland to California, from northern Canada 

to northern Y akutia across Beringia, across Siberia to the 

Ural Mountains and westward through Kazakhstan and the 

Ukraine to central Europe (but not to France or Holland), a 

common early Pleistocene form of Lasiopodomys was 

present that is much less advanced toward Microtus than 

most fossil or living species of the Oriental faunal region. If 

the remains of living Lasiopodomys brandtii were found in 

the United States, they would be thought to be a primitive 

species of Microtus and possibly more than 800,000 years 

old. Compare figure 11N (living Lasiopodomys brandtii) 

with figure 12A (820,000 year old primitive Microtus 

paroperarius from Colorado) and with figure 12C (a fossil 

representative of the living Microtus nivalis from Czechoslovakia). Both of these examples of Microtus can have a 

simple last upper molar; that of the illustrated specimen of 

Microtus paroperarius (a gigantic individual) is also illustrated (fig. 12A). 

In view of the "atypical" morphology of most Lasiopodomys species from the Oriental faunal region (where the 

genus exclusively lives today), the present author has taken 

the liberty of declaring the more primitive form known in the 

fossil record of the rest of the Northern Hemisphere as having the "typical" first lower molar morphology of the genus 

(fig. 11B-G). 

The extinct fossil species Lasiopodomys deceitensis 

(Beringia and North America) and (or) L. ratticepoides 

(Eurasia exclusive of Beringia) are considered typical for the 

genus. L. deceitensis, described (as Microtus deceitensis) 

from the Cape Deceit fauna of Alaska (Guthrie and 

Matthews, 1971), has more frequent posterobuccal angular.:. 

ities on the Cap than do some. (See figs. 11, 15, 16, and 17.) 

L. ratticepoides was described (as Microtus ratticepoides) from the Upper Freshwater Bed at West Runton, 

England, by Hinton (1923). It is considered by many to be 

ancestral to those living species of Microtus that have a relatively simple frrst lower molar, such as M. oeconomus. This 

may be so, but M. oeconomus has a complex last upper 

molar, and Lasiopodomys does not. The last upper molar of 

Microtus (or Lasiopodomys) ratticepoides has never been 

identified, and may not be cited in defense of the generic 

assignment. It is, therefore, possible that the form from European late Biharian faunas (Koneprusy C-718 and Upper 

Freshwater Bed) may indeed have a complex M\3 and may 

be ancestral toM. oeconomus, while middle Biharian faunas 

(Holstejn, Chlum 6, and. Valerots) may have a simple M\3 

and might be called "L. preratticepoides." This possibility 

cannot be confirmed without further examination of the collections. Lacking this, one cannot say when Lasiopodomys 

became extinct in Europe. 

The distinctively different history of evolution of 

Lasiopodomys in the Oriental faunal region is one of several 

examples illustrating the relative isolation of this region, 

indicating its provincial faunal nature. Other examples 

among the microtines will be mentioned, and Flynn and 

others ( 1991) have suggested a similar provincial isolation 

because of other and older aspects of the Chinese fossil 

fauna. 

The recognition of a separate genus Lasiopodomys is a 

compromise: It provides a name for intermediate forms that 

have been assigned either to the more primitive Allophaiomys or to the more advanced Microtus. The evolutionary 

history, dispersal patterns, and environmental preferences of 

Lasiopodomys are different than those of the genera to which 

it has been elsewhere assigned. Therefore, its recognition as 

a distinct taxon is informative. This recognition permits the 

definition of Allophaiomys as limited to an open Dimension 

C-C' and that of Microtus as beginning with the presence of 

Dimension A-A'. The morphologic limits of these two genera, respectively the ancestor and the descendant of Lasiopodomys, have been too vague in previous delineations of these 

genera. 

Erbaeva (1976) was the first to assign "typical," primitive fossil forms to the genus Lasiopodomys; advanced fossil 

forms from China, assigned to the genus much earlier 

(Young, 1934), differ little from the living species and indicate a different, but parallel, history in the Oriental faunal 

region. Repenning (1980) followed Erbaeva' s usage of 

1976. 

Character evolution.- "Intermediate" enamelthickness differentiation is most common in fossil populations of Lasiopodomys, although "Mimomys" differentiation 

is known (fig. 16A) and most, but not all, advanced forms 

have "Microtus" differentiation. 

Evolutionary advancement of the genus is marked by 

increasing percentages of "Microtus" enamel-thickness differentiation, increasing prominence of either or both lingual 

and buccal posterior angularities on the Cap (eventually 

leading to Secondary Wings in Microtus), and narrowing of 

Dimension B-B' (fig. 11). These changes lead to the living 

species of Lasiopodomys, and to the genus Microtus. 

The most primitive described morphotype of Lasiopodomys is found in the species Lasiopodomys praebrandtii, 

described by Erbaeva (1976) from the Kudun fauna of 

Buryat A.S.S.R., south of Lake Baikal. In this species, reduction of Dimension C-C' is evident only in some individuals. 

Reduction is never complete, never completely closing the 

buccal Primary Wing to form Triangle 4 (Repenning and 

Grady, 1988, fig. 4B). The generic assignment has been 

questioned (M.A. Erbaeva, oral common., 1987). Depending 

upon morphotype percentages within the sample, the species 

might be more appropriately considered an advanced species 

of Allophaiomys, but population characteristics are not available. As the species is not in question, the intermediate 
48 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

arbitrary name might be "Allophaiomys-Lasiopodomys 

praebrandtii." 

Lasiopodomys praebrandtii is a small species, having a 

first lower molar that is little more than 2 mm long. The 

small size may be a provincial character, as Zheng and Cai 

(1991) have recently described Lasiopodomys probrandtii 

from Weixian County, Hebei Province, P.R.C., that is morphologically similar to Lasiopodomys deceitensis, but 

smaller. The sample was of fairly large size. Zheng and Cai 

have considered L. probrandtii to be as old as about 1.2 million years, roughly the same age as older records of the 

derived L. brandtioides, which suggests the existence of two 

lineages of Lasiopodomys in China, one of which is smaller 

and has an evolutionary rate more comparable with that of 

extra-Chinese Lasiopodomys. 

The age of the Kudun fauna has not been determined by 

external evidence. It is here believed to be about the age of 

the Olduvai event on the basis of the associated fauna. No 

other record of Lasiopodomys is thought to be as old. 

''Typical" forms have been described from central 

Europe to China, but have been listed as Allophaiomys or 

Microtus; some of these clearly show an individual variation 

of morphotypes overlapping that of Allophaiomys, but none 

show a mode so apparently intermediate as that from the 

Kudun faurta, and none are securely dated. 

When and where Lasiopodomys first evolved out of 

Allophalomys is not at all clear. One is impressed with the 

liuggestion of mosaic evolution, but frustrated in the effort to 

recognize a pos&ible center of origin by the lack of external 

time control. 

By the diagnosis here used, the living species of 

Lasiopodomys (L brandtii and L. mandarinus) and some 

advanced Chinese fossil species, such as Lasiopodomys 

brandtioides (Young, 1934), have primitive Microtus first 

lower molar morphotypes; they have a weak development of 

at least the lingual Secondary Wing on the Cap of first lower 

molar (fig. 11N, 0). The presence of a simple last upper 

molar is not universally exclusive of Microtus, as the earliest 

forms of this genus had simple last upper molars and some 

living lineages retain them. The living species of Lasiopodomys could be considered as primitive species of Microtus 

as here defined. 

As here defined, based on the character states of fossil 

species included in the genus, Lasiopodomys is a genus intermediate between ancestral Allophaiomys and derived Microtus. With the exception of Lemmiscus, which evolved 

directly out of Allophaiomys in the United States, and 

Proedromys, whose derivation is not yet known, Lasiopodomys initiates the lineage of the tribe Microtini and leads to 

the obviously polyphyletic genus Microtus (fig. 14). 

Although overlapping individual variability correctly 

indicated to Chaline (1972) that Microtus evolved from 

Allophaiomys, a conclusion that this evolutionary sequence 

is documented in France is not indicated by the faunas 

Chaline considered. He described no fauna with a population 

of "typical" Lasiopodomys, although he illustrated advanced 

forms of Lasiopodomys (with prominent lingual and buccal 

posterior angularities on the Cap) under the name Microtus 

nivalis, from the localities Combe Grenal, Regourdou, and 

Hortus (Chaline, 1972, figs. 58 and 59). Only one individual 

variant described by him is a "typical" morphotype; it is 

from Regourdou (no. 10 of his fig. 58). 

To judge from the illustrations of Chaline (1972), 

Lasiopodomys (or the Lasiopodomys morphotype in primitive Microtus populations) was an immigrant to France at a 

late date, possibly middle to late Biharian, and at an 

advanced stage; the beginning of the tribe Microtini took 

place elsewhere. 

Discussion.-That the application of names to forms 

here included in the genus Lasiopodomys varied greatly led 

directly to the misunderstanding of the age of the Olyor Suite 

in Y akutia, which stimulated this discussion. It also led to the 

invalid conclusion that the age of the Olyor Suite was comparable to that of the Karay-Dubina fauna of the Ukraine. It 

was not realized that what was called Allophaiomys in the 

Olyor faunas was called Microtus in the Karay-Dubina 

fauna. Each misunderstanding, based as it was upon acceptance and use of names that appeared in published lists rather 

than upon comparison of specimens, led to erroneous interpretations of the paleomagnetic patterns and thus to errors in 

temporal correlation nearly as great as a million years. 

As here used, the morphologic point of first discrimination of Lasiopodomys of tribe Microtini from Allophaiomys of tribe Arvicolini is the essential closure of 

Dimension C-C' (fig. 10), separating the Primary Wings of 

the Anteroconid Complex and producing Triangle 4 in an 

otherwise typical Allophaiomys first lower molar (fig. 11). 

This is the only consistent dental character that defines the 

morphologic beginning of Lasiopodomys and the tribe 

Microtini. It is a character completely lacking in the type 

population of Allophaiomys pliocaenicus and, hence, in the 

genus. 

Except in the Oriental faunal region, the first point of 

discrimination of Microtus from Lasiopodomys lies in the 

development of one or both Secondary Wings on the Cap of 

the Anteroconid Complex of the frrst lower molar of Microtus (Repenning and Grady, 1988). This is the only consistent 

Figure 11 (facing page). Lasiopodomys. A, Lasiopodomys sp., 

Anza-Borrego Desert, California; LACM specimen; outline dashes 

indicate incomplete parts of specimen. B, Lasiopodomys ratticepoides, Locality C718, Czechoslovakia. C-K, Lasiopodomys deceitensis from: C, County Line, Illinois; ISM specimen. D-1, 

Cheetah Room fauna, West Virginia; USNM specimens. J, K, 

Cheetah Room fauna, individuals overlapping Microtus morphology; USNM specimens. L, M, ? Lasiopodomys sp., advanced morphology from Hanover Quarry Fissure, Pennsylvania (sample 

consists of three specimens); CMNH specimens. N, Lasiopodomys 

brandtii from Inner Mongolia, P.R.C., living species; USNM specimen. 0, Lasiopodomys mandarinus from Korea, living species; 

USNM specimen. 
GENUS LASIOPODOMYS 49 

0 1 2mm 
50 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

dental character that defines the morphologic beginning of 

Microtus, as here defined, and even this character state is 

violated by the advanced state of living Lasiopodomys and 

similarly advanced fossil forms of eastern Asia. 

In the consideration of the earliest records of Microtus 

paroperarius that follows, the development of Secondary 

Wings in the living Lasiopodomys species of eastern Asia is 

regarded as independently derived, and Microtus is recognized in the United States and Eurasia (excluding the Oriental region) with the first modal development of one or both 

of these wings. Although not always developed, a great 

reduction in Dimension B-B', forming Triangle 5 on the first 

lower molar, and the development of a complex last upper 

molar are also indicative of Microtus. 

In the introductory section on Conventions, it was 

stated that the system of diagnostic dimensions followed that 

of van der Meulen (1973) with one significant addition 

called Dimension A-A', the distance between the reentrants 

anterior to the secondary wings of the present report (fig. 

10). Van der Meulen (1973; 1978) actually recorded this 

dimension, naming it dimension D-D' -the width of the 

Cap. He considered it to be present in Allophaiomys, in 

which no reentrants are present on the Cap, and to be present 

in morphologically advanced forms with Secondary Wings, 

such as are shown in figure 10 of the present report. In these 

advanced forms van der Meulen's dimension D-D' does not 

show the width of the Cap, but rather the narrowness 

between the reentrants on the Cap anterior to the Secondary 

Wings. When reentrants are present (making Secondary 

Wings), van der Meulen's dimension D-D' is always less 

than the width of the Cap (van der Meulen, 1973, fig. 22) and 

it corresponds to the Dimension A-A' of the present report; 

when reentrants are not present, van der Meulen's dimension 

D-D' is the width of the Cap (van der Meulen, 1978, fig. 3), 

but the Dimension A-A', as herein used, does not exist. 

To avoid possible confusion in usage, a Dimension 

A-A' (an alphabetical symbol not used by van der Meulen) 

is used in the present report and it is not considered the 

same as van der Meulen's dimension D-D'. The Dimension 

is considered to be present only when reentrants have 

developed anterior to the Secondary Wings; it is not 

present in Allophaiomys or typical Lasiopodomys, whereas 

van der Meulen's dimension D-D' is. 

The transition of Microtus out of Lasiopodomys or 

Lasiopodomys out of Allophaiomys is understood to take 

place within the modal morphology ofthe population; it may 

not be represented in individual variants of low abundance in 

populations. An Allophaiomys-Lasiopodomys transitional 

fauna, showing this origin of the Microtini, is not known 

from North America. Lasiopodomys evolved from Allophaiomys in Eurasia, and both genera dispersed to North America, but at greatly different times. 

Little difference in the morphology of different North 

American populations of Lasiopodomys has been recognized, and nearly all are assigned to Lasiopodomys 

deceitensis (Guthrie and Matthews) (1971), named (as 

Microtus deceitensis) from the Cape Deceit fauna of Alaska. 

(See fig. 17 .) The present author is currently unable to separate L. deceitensis from Eurasian Lasiopodomys ratticepoides (Hinton) (fig. liB), but retains the separate names 

until further study can be made. It is considered possible that 

the genus Lasiopodomys is not represented by the type population of Microtus ratticepoides Hinton, as the last upper 

molar has not been described. If it were complex, the species 

ratticepoides should remain in the genus Microtus. 

LASIOPODOMYS FROM THE ANZA-BORREGO DESERf 

(fig. 11A; locality 21, fig. 1) 

In the Anza-Borrego Desert of southernmost California 

(lat 33°10' N.), 39 miles (62 km) north of the border of 

Mexico, west of the Salton Sea and on the western flank of 

the Imperial Valley, lies an extensive and continuous exposure of sediments extending upward from the marine Imperial Formation, of late Miocene and early Pliocene age, 

essentially to the top of the lower Pleistocene (Downs and 

White, 1968). The section has paleomagnetic control from 

the Nunivac Normal-polarity Subchron of the Gilbert 

Reversed-polarity Chron to what has been assumed to be the 

Jaramillo Normal-polarity Subchron of the Matuyama 

Reversed-polarity Chron (Johnson and others, 1984), but 

which must represent the beginning of the Brunhes Normalpolarity Chron. 

Sedimentation rates have been calculated throughout 

this section and, in that part between the Olduvai and the purported Jaramillo events, there appears to have been very little 

variation (Johnson and others, 1984). Terricola meadensis 

(fig. 1 OB) was found in this part of the Anza-Borrego Desert 

section (the Vallecito Creek fauna; LACM Locality 68123, 

specimen number LACM 24828) below the youngest normal 

magnetic interval in a continuous part of the section with 

other faunas used in characterization of the late Vallecito 

Creek mammalian fauna (J.A. White, written common., 

1990). There is no recor4 of Terricola meadensis in the 

United States that is as old as the Jaramillo event and this 

immigrant indicates an age younger than 850,000 years. 

Thus the youngest normal-polarity zone represents the 

Brunhes Chron, and sediment rates must be less than was 

calculated on the basis of this polarity being the Jaramillo 

event. More importantly, at least one period of nondeposition is indicated by the lack of a record of the Jaramillo event 

in the section. This decreasing depositional rate, with gaps of 

no deposition, is more consistent with the subsequent record 

of orogenic activity that resulted in elevation and the cessation of all deposition in the Anza-Borrego part of the former 

basin (Johnson and others, 1984). 

Although microtine rodents are not common in the 

Anza-Borrego Desert deposits because of the southern location, a few of some significance to the present discussion 
GENUS l.ASIOPODOMYS 51 

have been recovered: Microtus, Lasiopodomys, and, as just 

mentioned, Terricola (figs. lOA and B, and llA). Figure llA 

shows the only tooth with a Lasiopodomys morphotype from 

the Vallecito Creek faunal sequence in the Anza-Borrego 

Desert. It is a very damaged specimen, but what is preserved 

clearly indicates that it is a Lasiopodomys morphotype. It is 

the only microtine tooth from LACM Locality 1942 

(ANZA-2 on fig. 14), which is 540 feet (164.6 m) below the 

Brunhes Chron and 1 ,000 feet (304.8 m) above the Olduvai 

normal event (J.A. White, written commun., 1990). Assuming the uniform depositional rates that have been calculated 

(Johnson and others, 1984), it is about 1.10 million years old. 

This is older than the Jaramillo event, which was not 

recorded in the section, and therefore the age should be older 

than this calculation by at least the duration of this event 

(70,000 years) or about 1.17 million years. An age of about 

1.2 million years is thus assumed for the specimens of 

Lasiopodomys, although it is not possible to judge what other 

irregularities in deposition are present in the long reversely 

polarized section. Although quite speculative, this approximate interpolated age is quite close to a Northern Hemisphere cold period (Repenning and Brouwers, 1992) that 

climaxed just before the Cobb Mountain Normal-polarity 

Subchron (1.10 Ma), suggesting a correlation between the 

southward dispersal of Lasiopodomys from Beringia and 

climate change. 

Although imperfectly preserved and inadequate as a 

representative sample of the population, what is preserved 

(fig. llA) is clearly a Lasiopodomys morphotype; and it 

seems probably older than the oldest immigrant Lasiopodomys to the east of the Rocky Mountains (about 840,000 

years old). It provides some suggestion of the possible age of 

the genus and also a suggestion of differing dispersal and 

evolutionary histories on either side of the Rocky Mountains 

of North America. The last suggestion has been discussed in 

consideration of the Allophaiomys and Microtus from 

Wellsch Valley, Saskatchewan, and is discussed again in the 

section, "Provinciality." This is the only known specimen of 

Lasiopodomys from west of the Rocky Mountains. 

LASIOPODOMYS FROM THE CHEETAH ROOM FAUNA 

(fig. 11D-K; locality 17, fig. 1) 

The Cheetah Room fauna of Hamilton Cave, West 

Virginia, was discussed previously in connection with its 

Allophaiomys population. It is believed to be about 840,000 

years old on the basis of its fauna (Repenning and Grady, 

1988). The ample sample of Lasiopodomys deceitensis (36 

M/1 s in the sample seen; as noted previously, the entire sample was not seen) is apparently the oldest record south of 

Beringia on the east side of the Rocky Mountains of North 

America; it is younger than the specimen of Lasiopodomys 

from California and from Beringia. 

One specimen of Lasiopodomys deceitensis from the 

Cheetah Room fauna (USNM 264316) has associated upper 

and lower dentition, and is the only fossil record of physically associated upper and lower dentition of this genus 

known to the author. The last upper molar of the individual 

with associated first lower molars is simple, as is equally 

indicated by the isolated teeth from the fauna. 

Nonbimodal (unimodal) morphologic overlap was 

described in the separation of Microtus morphotypes from 

the Lasiopodomys population of the Cheetah Room fauna 

(Repenning and Grady, 1988). The Microtus morphotype 

was very primitive and of minor proportion (25 percent) in 

this population, and thus it should have been viewed only as 

an extreme in the individual variation of Lasiopodomys. The 

strong single mode (75 percent) of Lasiopodomys in this 

fauna (fig. llD-1) was counted by considering even the 

slightest suggestion of a lingual Secondary Wing (fig. 111, 

K) as a Microtus morphotype; a much smaller number 

(perhaps 3 percent) were obvious morphotypes of Microtus 

(Repenning and Grady, 1988, fig. 4E). The presence of 

Microtus morphotypes in the Lasiopodomys population from 

the Cheetah Room fauna justifies a separate species name 

within Lasiopodomys, although none has been or is 

suggested. 

The most Microtus-like individual in the Cheetah 

Room fauna was illustrated by Repenning and Grady (1988, 

fig. 4E). Except that it is smaller, it is quite similar to the 

specimen shown from the older part of the Hansen Bluff 

faunal sequence (this report, fig. 12A; Repenning and Grady, 

1988, fig. 4K; these are left and right teeth of the same individual). This most advanced Microtus morphotype of 

Lasiopodomys from the Cheetah Room fauna resembles the 

primitive Microtus paroperarius morphotypes of Cumberland Cave (van der Meulen, 1978, figs. 11A, D, F, and G), 

and of Hansen Bluff (fig. 12A), and the more primitive variations of the typical population from the Cudahy fauna of 

Kansas (fig. 12B; also see Paulson, 1961, figs. 7 A-D and H). 

It is unlike the Lemmiscus morphotypes in the variation of 

Allophaiomys from SAM Cave, New Mexico, which, as has 

been noted, show development of primarily the buccal Secondary Wing (fig. 6F, G). 

Even these weak indications of the Microtus morphotype are not recorded in the very small sample from Hanover 

Quarry Fissure (fig. IlL, M), but this sample also has no 

typical morphotypes of Lasiopodomys deceitensis. The low 

variability of the population of Pitymys cumberlandensis 

from the Hanover Quarry Fissure fauna and the presence of 

Allophaiomys guildayi and typical Synaptomys indicate that 

the Hanover Quarry Fissure fauna is younger than the 

Cheetah Room fauna. 

As discussed in the later section, the Lasiopodomys and 

Microtus morphotypes in the Cumberland Cave fauna, 

Maryland, also lack a bimodal distribution in this population. 

The single mode is within the Microtus morphotypes, 

although very close to the defined boundary between this 
52 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

genus and Lasiopodomys. Three situations indicate that the 

Cumberland Cave fauna is more derived than the Cheetah 

Room fauna: (1) the Cheetah Room fauna contains a Lasiopodomys modal morphology (rather than the Microtus 

modal morphology in the Cumberland Cave fauna), (2) morphologic gradation occurs between Pitymys cumberlandensis and Allophaiomys in the Cheetah Room fauna 

(contrasting with the polarity of the Pitymys morphology in 

Cumberland Cave), and (3) the gradation between the lemmings Synaptomys and Mictomys in the Cheetah Room fauna 

(Repenning and Grady, 1988) contrasts with the morphologic polarity of these two genera in Cumberland Cave 

fauna. 

?LASIOPOIXJMYS FROM THE HANOVER QUARRY FISSURE 

FAUNA 

(fig. IlL and M; locality 16, fig. 1) 

The Hanover Quarry Fissure fauna was discussed previously in connection with its population of Allophaiomys 

guildayi. Its age is close to that of the Cumberland Cave 

fauna, but it may be slightly older because, although very 

small, the sample of ?Lasiopodomys sp. contains no Microtus morphotypes, whereas over half the population in Cumberland Cave was of Microtus morphotypes, and in the 

Hanover population of Allophaiomys guildayi a lower percentage of individuals exhibit a Pedomys morpho type than in 

the Cumberland Cave population (Guilday and others, 1984, 

p. 121). 

The few individuals (five were listed by Guilday and 

others, 1984, two more than were available for the present 

study) of ?Lasiopodomys were originally referred to Microtus paroperarius (Guilday and others, 1984) because they 

conform to morphotypes of Lasiopodomys that van der 

Meulen (1978) included in Microtus paroperarius when 

describing the Cumberland Cave fauna. Although not sufficiently derived to fit the morphologic definition of Microtus, 

the morphology of all three specimens is quite advanced for 

Lasiopodomys (fig. IlL, M). Salient angles are present at the 

positions of the Secondary Wings, but the Wings are not 

present; the anterior portion of the Cap is not enlarged so that 

the position, or existence, of Dimension A-A' is not indicated. In addition, the separation of Triangle 5 (the lingual 

Primary Wing) from the Cap is complete in one individual 

(fig. 11M), and reduction of Dimension B-B' is complete. 

?Lasiopodomys from Hanover Quarry Fissure is very close 

to living Lasiopodomys mandarin us (fig. 11 0), as are Microtus variants of Lasiopodomys from the Cheetah Room fauna 

(fig. llJ, K). 

Strict adherence to the definition of Microtus, as forms 

first being recognized with the development of Secondary 

Wings and a Dimension A-A', requires that these few individuals from Hanover Quarry Fissure be called advanced 

Lasiopodomys morphotypes. The morphology of these 

specimens is similar to some morphologies found in the 

Cumberland Cave samples that have been placed in Microtus 

paroperarius, but nearly half the Cumberland Cave population consists of Lasiopodomys morphotypes. 

The Hanover Quarry Fissure fauna contains nothing 

that resembles the frrst lower molar of typical Microtus 

paroperarius or of typical Lasiopodomys deceitensis. Without a population sample of sufficient size, determining the 

modal morphology is impossible, and generic assignment is 

uncertain. 

LASIOPOOOMYS FROM THE CUMBERlAND CAVE FAUNA 

(locality 11, fig. 1; illustrated in van der Meulen, 1978) 

The Cumberland Cave fauna of western Maryland has 

been discussed in connection with its population of Allophaiomys guildayi. As just mentioned, it also contains a population that was referred to the species Microtus paroperarius 

by van der Meulen (1978). He showed an overlap in variability between the morphotypes of Lasiopodomys (his figs. 

llB, C, and E) and Microtus (his figs. llA, D, F, and G) in 

this sample, although he referred the entire sample to M. 

paroperarius. 

Because van der Meulen did not consider Dimension 

A-A', the development of which is indicated by the appearance of the Secondary Wing or Wings that define Microtus, 

and did not indicate what percentage of the Cumberland 

Cave population has these morphotypes, it is not clear from 

his report what genus should be recognized in the fauna. 

A total of 178 first lower molars from the Cumberland 

Cave fauna are here assigned to Microtus paroperariusLasiopodomys deceitensis. These M/1 s are composed of 

"typical" Lasiopodomys deceitensis (15 percent) and 

"advanced" Lasiopodomys morphotypes having a posterolingual corner on the Cap similar to figure 111-M (26 percent). "Primitive" Microtus, with at least the lingual Secondary Wing in evidence (and often a weakly developed 

buccal one) similar to figures 110 and 128, C, or D, constitutes the largest part of the population (42 percent). A 

smaller portion ( 17 percent) is made up of "unquestionable" 

but still primitive Microtus paroperarius similar to forms 

from the oldest faunas of the Hansen Bluff faunal sequence, 

to a few morphotypes from the Cheetah Room fauna, and to 

the more simple morphotypes from the type population of 

the Cudahy fauna. All Microtus morphotypes thus make up 

59 percent of the population, although only 17 percent would 

be considered "typical" on the basis of the type population 

from the Cudahy fauna. There are no advanced, complicated 

Microtus morphotypes in the Cumberland Cave population 

as there are in the type population. "Microtus" enamelthickness differentiation was present in 71 percent of Microtus morphotypes and in 56 percent of Lasiopodomys 

morpho types. 
GENUS USIOPODOMYS 53 

The unimodal morphological variation has its mode 

very close to the diagnosed taxonomic boundary between the 

definitions of Lasiopodomys and Microtus. Diversification 

into two distinct species is not indicated; the anagenetic evolution of one population, grading from Lasiopodomys to 

Microtus, is. A slight percentage dominance of Microtus 

morphotypes suggests that the population might be called 

Microtus paroperarius, but it is very much a borderline situation, and the hyphenated name Microtus paroperariusLasiopodomys deceitensis is here assigned. It would be, and 

has been, very misleading to assign the entire population to 

either of these defined species and genera. 

The Cumberland Cave fauna of Maryland records the 

evolution, in the United States, of Microtus paroperarius out 

of Lasiopodomys deceitensis. This independent evolution of 

one species of Microtus postdates many older records of 

Microtus species, which had evolved out of Lasiopodomys in 

regions other than the United States. It was not until about 

450,000 years ago that species of these older lineages of 

Microtus first entered the United States east of the Rocky 

Mountains. The oldest record may be in the undated Porcupine Cave fauna of south-central Colorado, which contains 

both immigrant Microtus and native M. paroperarius 

(Barnosky and Rasmussen, 1988). With the immigration of 

Beringian-Asian Microtus to the United States, M. paroperarius appears to have become extinct, and no younger 

records exist. 

Nearly half the population of Microtus paroperariusLasiopodomys deceitensis from Cumberland Cave consists 

of Lasiopodomys morphotypes, which should have been 

associated with simple last upper molars, and some of the 

simplest morphotypes of Microtus paroperarius also should 

have had associated simple last upper molars. Because typical Microtus paroperarius (from Cudahy, Kansas) has complicated last upper molars, van der Meulen (1978) assigned 

only complicated last upper molars from the collection to 

this species. No associated upper and lower dentitions 

appear to have been collected in Cumberland Cave. Of the 

total last upper molars collected, the number that he assigned 

to this species is reasonably proportionate to the number of 

first lower molars with Microtus morphotypes. It is probable, 

therefore, that some of the simple last upper molars from the 

Cumberland Cave fauna, which van der Meulen (1978) 

assigned to Pitymys and Pedomys, belong to more primitive 

morphotypes of the Microtus-Lasiopodomys population. 

If the two first lower molar morphotypes from Cumberland Cave that van der Meulen included in Microtus paroperarius are not recognized as representing separate generic 

morphotypes, the use of the generic name Microtus would 

also be made acceptable for Lasiopodomys deceitensis. For 

example, Guilday and others (1984) identified the first lower 

molars of a Lasiopodomys morphotype (fig. IlL, M) from 

the Hanover Quarry Fissure fauna as M. paroperarius 

because they match the Lasiopodomys morphotypes that van 

der Meulen (1978) included in this species of Microtus from 

Cumberland Cave. Also, the single tooth of Lasiopodomys 

from the County Line fauna of Illinois was assigned to M. 

paroperarius on this basis (Miller and others, 1987). 

It is generally agreed that the lineage leading to 

Microtus is Mimomys-+Allophaiomys-+Lasiopodomys-+ 

Microtus. If Microtus is acceptable as the generic assignment for species with a Lasiopodomys morphotype, then, 

by extension, the same logic would be acceptable for 

Allophaiomys morphotypes in faunas of Lasiopodomys 

(possibly the Razdolie fauna). Microtus could thus become 

acceptable as the generic assignment of typical Allophaiomys pliocaenicus. 

By further extension, primitive populations of Allophaiomys, with some individuals having less hypsodonty 

and rooted teeth, would then become acceptable as representatives of the genus Microtus. Ultimately the species now 

assigned to Mimomys and the subfamily Arvicolinae could 

have a history represented by the single genus Microtus. The 

purpose of taxonomy is to identify definable stages in a 

known history, and such treatment would identify very few. 

The majority of population morphotypes must conform to 

existing diagnoses. 

Although this hypothetical possibility seems unlikely, it 

should be pointed out that Chaline (1972) has done exactly 

this, except in reverse, and has projected the generic name 

Allophaiomys well into the definitions of the genera Microtus and Pitymys by allowing nomenclature to follow gradation beyond the limits of diagnosis. 

Chaline did not have complete gradation. Microtus did 

not evolve out of Allophaiomys in France any more than it 

did in North America; it originated elsewhere in faunas possibly older than any French localities considered by Chaline 

and immigrated to France and to North America. In nearby 

Holland, Allophaiomys became extinct before Microtus first 

appeared (van Kolfschoten, 1988). 

In his treatment Chaline ( 197 4) did nothing more, in 

fact, than did van der Meulen (1978) when he enlarged the 

definition of the species Microtus paroperarius to include 

atypical morphologies here called Lasiopodomys deceitensis. VanderMeulen had, in his study collection, specimens 

of Guthrie and Matthews' (1971) L. deceitensis (in the terminology of the present report), but apparently did not realize 

that part of his population of M. paroperarius was identical 

to L. deceitensis. 

Although slightly more than 50 percent of the population from Cumberland Cave has a Microtus morphotype, the 

morphologic borderline condition of the population mode 

indicates that the identification Microtus paroperariusLasiopodomys deceitensis should be used in order to prevent 

creating the impression that all of the morphologies present 

are truly Microtus. As mentioned, several published references (Guilday and others, 1984; Miller and others, 1987, for 

example) identify typical L. deceitensis morphotypes as M. 

paroperarius on the strength of the name that van der 

Meulen gave to this Cumberland Cave population. The 
54 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

admittedly awkward device of a hyphenated name is here 

adopted to point out the morphologically intermediate nature 

of the population from Cumberland Cave and to avoid the 

inference that Lasiopodomys morphotypes can be included 

in the genus Microtus. 

In addition to the lack of Allophaiomys, no Lasiopodomys morphotypes were present in the samples of Microtus 

from the oldest faunas of Hansen Bluff. These population 

conditions suggest that the Cumberland Cave fauna is older 

than the oldest faunas of Hansen Bluff (820,000 years) and 

older than was suggested by Repenning (1987); it is about 

the age that van der Meulen (1978, fig. 14) indicated. 

As has been discussed, Cumberland Cave is younger 

than the Cheetah Room fauna (approximated at 840,000 

years) on the basis of its having (1) a lack of individual variation in Synaptomys cooperi overlapping the genus Mictomys, as is present in the Cheetah Room fauna; (2) a very 

primitive Microtus paroperarius morphologic mode within 

a Microtus-Lasiopodomys population, rather than a Lasiopodomys population that overlaps Microtus in its variability; 

and (3) Pitymys cumberlandensis with no overlap of Allophaiomys in its morphologic variation. All these conditions 

are more progressive than has been documented in the Cheetah Room fauna (Repenning and Grady, 1988). The Cheetah 

Room fauna is less than 850,000 years old because it contains the Old World immigrant Lasiopodomys. 

The Cumberland Cave fauna is here arbitrarily considered 830,000 years old, intermediate between the oldest part 

of the Hansen Bluff faunal sequence, which indicates a more 

advanced fauna, and the older Cheetah Room fauna. All 

these faunas lived shortly before the Brunhes Normalpolarity Chron, by the time of which Microtus paroperarius 

contained advanced individual variants, and after 850,000 

years ago, when Lasiopodomys and Terricola immigrated 

into the United States. 

LASIOPODOMYS FROM THE COUN1Y LINE FAUNA 

(fig. llC; locality 20, fig. 1) 

The County Line locality lies near the Mississippi River 

in central Illinois and is under study by Miller and others 

(1987). These authors have reported mollusks, insects, 

pollen, plant megafossils, and mammals from the locality, as 

well as reversed paleomagnetic polarity. A single first lower 

molar of a microtine rodent was found and was reported as 

Microtus paroperarius (Miller and others, 1987), an identification that is acceptable under the identification used by 

van der Meulen (1978), but not by morphologic definition as 

here explained. The tooth is typical of Lasiopodomys 

deceitensis (fig. 11 C) and, as such, is in agreement with the 

inference that the reversed magnetic polarity represents the 

late Matuyama Chron. 

Although the population characteristics of the single 

specimen from the County Line fauna are unknown, the 

morphotype from the County Line locality (fig. 11 C) is that 

of typical Lasiopodomys deceitensis, rather than an 

advanced form of Lasiopodomys that could possibly be associated with some Microtus morphotypes. It could be an 

individual representing a very minor percentage of a population like that from Cumberland Cave (15 percent), but its 

"typical" morphology suggests that it more likely is from a 

more typical population of Lasiopodomys. Consequently, it 

is questionably referred to L. deceitensis until a larger sample might establish that the nature of the population differs 

from what is suggested by the single tooth. In such rapidly 

evolving and individually variable lineages, no certain identification of so small a sample is possible. 

The age suggested by this tooth from the County Line 

locality is equal to or greater than that of the MicrotusLasiopodomys fauna of Cumberland Cave (±830,000 years 

old). It could be as old as the Lasiopodomys-with-Microtusvariations fauna of Cheetah Room (±840,000 years old). It 

cannot be older than the approximated 850,000-year-old 

immigration of Lasiopodomys into the United States, and 

cannot be as young as the 820,000-year-old faunas in the 

Hansen Bluff sequence, which appear to postdate all 

Lasiopodomys morphotypes in the United States. 

To 1992, further collecting of the locality has failed to 

produce additional microtine fossils (R.W. Graham, oral 

commun., 1990). 

LASIOPODOMYS FROM THE LOCALI1Y CRH-47 FAUNA 

(locality 25, fig. 1) 

Locality CRH-47, along the Old Crow River in northem Yukon Territory, Canada, is near the Canada-Alaska 

border and about 100 miles ( 161 km) south of the Arctic 

Ocean in easternmost Beringia. The locality was discovered 

by C.R. Harington and contains a very large microtine rodent 

fauna that is under study by R.E. Morlan of the Archaeological Survey of Canada (R.E. Morlan, written commun., 

1991). The sediments at the locality have normal magnetic 

polarity (Schweger, 1989). This fauna has been discussed 

previously in consideration of the affinity of the Microtus 

associated with Allophaiomys from the Wellsch Valley 

fauna of Saskatchewan (p. 38). 

R.E. Morlan's examination of this fauna (written commun., i991; work in progress) indicated that it contains 

Phenacomys deeringensis, named from the Cape Deceit 

fauna of Alaska (Guthrie and Matthews, 1971; age uncertain 

and to be discussed). Locality CRH-47 also contains a species of Mimomys (Cromeromys) similar toM. (C.) virginianus from the Cheetah Room fauna of West Virginia 

(Repenning and Grady, 1988; ±840,000 years old) and toM. 

dakotaensis (Martin, 1989) from the Java fauna of South 

Dakota (1.9-1.4 Ma); the subgenus is older than the Brunhes 

Chron in both North America and Eurasia. 
GENUS I.ASIOPODOMYS 55 

R.E. Morlan (written common., 1991) noted a shift in 

the dental pattern complexity of the collared lemming 

Dicrostonyx upsection at CRH-47, which appears to conform to the changes in pattern from Dicrostonyx renidens 

into D. simplicior, and, accordingly, he has referred the timeaveraged sample to D. renidens-simplicior. This identification is in accord with an assignment of the normal polarity of 

the locality to the Jaramillo event, as D. simplicior was 

described from a middle Biharian fauna of Europe (Fejfar, 

1966) and D. renidens is more primitive (Zazhigin, 1976). 

Zazhigin (in Sher and others, 1979) recognized the earliest 

D. renidens from Locality KL0-9 of the Krestovka Sections, in the uppermost part of the older member of the Olyor 

Suite (lila), to be discussed in the final section of this report, 

"Age of Krestovka Olyor and Cape Deceit faunas." In that 

discussion, Locality KL0-9 is assigned an age of about 1.1 

million years, 200,000 years older than the Jaramillo event. 

The fauna from CRH-4 7 also contains Lasiopodomys 

deceitensis (also described from the Cape Deceit fauna) and 

an assortment of Microtus that includes morphotypes similar 

toM. paroperarius as well as forms that seem to be early representatives of several advanced living species (R.E. Morlan, written common., 1991). Lasiopodomys became extinct 

farther south (in the United States) before the Brunhes 

Chron. It also became extinct in western Beringia before the 

Brunhes Chron (Sher and others, 1979, as Allophaiomys). 

Of considerable significance in the Old Crow faunas, 

including CRH-4 7, is the total lack of Allophaiomys and of 

members of the Pitymyini; this lack in both eastern (Old 

Crow) and western (Krestovka) Beringia suggests a period 

of erosion, rather than deposition due to lowered sea level 

caused by the accumulation of ice on the continents. These 

genera were and are temperate-climate animals and they 

must have passed through Beringia during marked warm 

periods immediately following or preceding major continental glaciation. Allophaiomys passed through Beringia to 

North America just before the Olduvai event, no more than 

100,000 years after a peak in continental glaciation extended 

south to the State of Iowa and during a remarkably warm 

period throughout the Northern Hemisphere. Terricola, of 

the tribe Pitymyini, entered the United States 850,000 years 

ago, just prior to the frrst of the glacial advances that have 

been called Nebraskan in North America (Repenning and 

Brouwers, 1992). 

It now appears virtually certain that the normal polarity 

of Locality CRH-47, Old Crow basin of Yukon Territory, 

represents the Jaramillo Normal-polarity Subchron. This 

indicates that the fauna, containing no Allophaiomys, is of 

the same approximate age as the older faunas of SAM Cave, 

New Mexico, containing only Allophaiomys. Locality 

CRH-47 may be slightly older than the Wellsch Valley 

fauna of southern Saskatchewan that is intermediate in latitude and faunal composition, and contains both Allophaiomys (which still survived to the south) and Microtus 

(known at this time primarily to the north in Beringia), as has 

been discussed (p. 38). 

The late derivation of Microtus in the Cumberland Cave 

fauna of Maryland (± 830,000 years old) is clearly an event 

uniquely occurring in the United States to the east of the 

Rocky Mountains, because in southern Canada east of the 

Rocky Mountains and at two localities in California, west of 

the Rocky Mountains, advanced Microtus lived during the 

reversed polarity before the Brunhes Chron, and even before 

the Jaramillo event in the Anza-Borrego Desert of 

California. 

It does not seem that Locality CRH-47 can be as young 

as the Brunhes Chron; it contains Lasiopodomys, Mimomys 

(Cromeromys) sp. cf. M. (C.) virginianus, and Dicrostonyx 

renidens (R.E. Morlan, written common., 1991) not known 

anywhere in the world as recently as the Brunhes Chron. Nor 

are these forms known from localities as old as the Olduvai 

event. But Locality CRH-47 is normally polarized; it can 

only represent the Jaramillo event. 

This age interpretation is further supported by a consideration of the climate indicated by the plant remains from 

CRH-47 when compared with other records of the arctic 

region. These climatic factors are discussed in consideration 

of the age of the lower part of the Olyor Suite to follow, and 

by Repenning and Brouwers (1992). 

Led by the similarities of parts of this fauna to the Cape 

Deceit fauna of Alaska, earlier reports by the present author 

(especially Repenning, 1984) correlated the normal polarity 

of Locality CRH-47 with the Olduvai event. This age 

assessment was reinforced by his misconception regarding 

the age of the Krestovka Olyor Suite (similar to that of the 

Cape Deceit fauna), as will be discussed. However, as further information was gathered about the little-known microtine historical sequence between the Olduvai and Jaramillo 

polarity events (the greatest lacuna in microtine biochronology), this opinion became increasingly questionable, as 

stated by Repenning and Grady (1988), for two reasons. 

First came the realization that Lasiopodomys deceitensis had a rather long temporal range (Repenning and Grady, 

1988). As has been discussed, Lasiopodomys lived until just 

before the Brunhes Chron in several faunas of the United 

States, and its oldest dated record is about 1.2 million years 

old, although some undated localities (especially the Kudun 

fauna of Buryat A.S.S.R.) may be as old as the Olduvai 

event. 

Second, with his visit to Moscow in 1990, the author 

learned that his original concept of the age of the Olyor 

Suite of the Krestovka Sections was in error, as explained 

in the section, "Explanation of the problem." This information greatly strengthened the author's confidence in the biochronology of the collared lemmings, Predicrostonyx and 

Dicrostonyx, and required the revision of those correlations 

influenced by the previous interpretations of the age of the 

Krestovka Olyor, the Cape Deceit fauna and Locality 

CRH-47. 
56 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Critical to the correlation of faunal history, the fauna 

from Locality CRH-47 provides strong evidence of far 

greater diversification of Microtus than is known in considerably younger faunas of the United States. At the time when 

Locality CRH-47 was deposited, only Allophaiomys was 

present in the United States east of the Rocky Mountains; 

Lasiopodomys and Terricola were not introduced into the 

United States until 50,000 years ·after the Jaramillo event. 

And although Microtus paroperarius evolved out of immigrant Lasiopodomys in the eastern United States perhaps 

80,000 years after CRH-47 was deposited, Beringian Microtus did not enter the United States to the east of the Rocky 

Mountains until about 450,000 years after the CRH-47 

fauna lived, marking the beginning of the Irvingtonian III 

small mammal age (Repenning, 1987; as Rancholabrean 1). 

Latitudinal provincialism is prominent in micro tine history. 

Lasiopodomys is an abundant part of the CRH-47 fauna 

and continued to be present in apparently younger faunas of 

the Old Crow basin (at Localities· CRH-11 and CRH-64 as 

"Microtus sp. X" (Morlan, 1984, fig. 3)) coexisting with an 

increasing variety of advanced Microtus morphotypes. 

Age relationships of the Old Crow basin faunas are still 

under study, but all these faunas that contain Lasiopodomys 

are in normally magnetized deposits. If Lasiopodomys 

became extinct in Yukon Territory before the Brunhes 

Chron, as it did in western Beringia (as Allophaiomys) and in 

the United States (where it is not known after about 825,000 

years ago), all Lasiopodomys-bearing faunas of the Old 

Crow basin would appear to date from the Jaramillo event. 

However, at present no evidence suggests that 

Lasiopodomys became extinct in eastern Beringia at the 

same time that it did in the United States and Y akutia with 

the exception of those arguments presented above. 

GENUS MICRGIUS SHRANK, 1798 

(fig. 12E; Germany; locality 32, fig. 1, exact locality uncertain) 

Type species.-Mus arvalis Pallas, 1779; = Microtus 

terrestris Shrank, 1798. 

Revised dental diagnosis.-A genus of the tribe Microtim with Secondary Wing or Wings and a Dimension A-A'. 

Last upper molar simple or complex. 

"''YPICAL" MICR01US 

Revised dental diagnosis.-As for the genus. 

Comment.-Living and some fossil Lasiopodomys 

from the Oriental faunal region overlap this diagnosis, as has 

been noted (p. 46). The generic name Lasiopodomys derives 

from this lineage, and the lineage appears to be unique to this 

province. Should further study indicate that these forms from 

the Oriental region are more properly considered as a separate lineage of Microtus, originating in this province at an 

early date, the use of Lasiopodomys for more simplified 

fossil forms of the Northern Hemisphere will become inappropriate. 

This is not implausible, to judge from the present fossil 

record: an extremely early, advanced Microtus is known 

from the United States west of the Rocky Mountains (fig. 

lOA and C; California localities 21 and 22; fig. 1) which 

could have had its origin (fig. 14; ANZA-1 and Irvington) in 

such an early form of Microtus in the Oriental faunal region. 

These early Californian Microtus survive as the living 

Microtus califomicus and have been mentioned in connection with the age of the Wellsch Valley fauna of 

Saskatchewan (p. 37). They will be further discussed in the 

major section, "Provinciality," which follows on page 74. 

As here used, Lasiopodomys appears earlier than 

Microtus in most fossil records, and thus the generic distinction is biochronologically useful as well as morphologically 

definable. As has been discussed, the lack of recognition of 

this distinction has caused considerable variation in identification, with consequent errors in biochronologic 

interpretation. 

Discussion.-The development of the first Secondary 

Wing is here considered to be marked by the first detectable 

indentation of the anterolingual surface of the Cap of the first 

lower molar, anterior to the posterolingual angularity, or 

comer, of the Cap found in advanced Lasiopodomys. The 

specimens of figure 111 and K, from the population of L 

deceitensis in the Cheetah Room fauna, were counted as 

Microtus morphotypes although they hardly differ from 

some associated teeth counted as advanced Lasiopodomys. 

The most developed Microtus morphotype from this population (Repenning and Grady, 1988, fig. 4E) is very similar to 

the specimens of figures 12A and 16D of the present report. 

The appearance of a complex last upper molar and, with 

minor exception, the extreme narrowing or closure of 

Dimension B-B' are features not found in extinct morphotypes of Lasiopodomys (but see the living species in fig. liN, 

0); they are also suggestive characters of Microtus, but are 

not always present in this genus. 

Other advanced characters not always present in Microtus are: (1) narrowing or closure of Dimension A-A', (2) 

prominent development of both Secondary Wings, (3) narrowing or closure of Dimension B-B' (forming Triangle 5 

out of the buccal primary wing), (4) closure of Dimension 

A-A' (forming Triangles 6 and 7), and (5) complication of 

the last upper molar by development of a posterior hook and 

lingual third reentrant. 

As here restricted the genus Microtus is large, complex, 

and unquestionably polyphyletic. The type species is M. 

arvalis (Pallas), and it incorporates all morphologic criteria 

(fig. 12E): Secondary Wings are well developed on the Cap 

of the Anteroconid Complex, the last upper molar is complex 

and has a posterior hook, and Dimension B-B' is narrow to 

closed. But exceptions to these characters are common 

among the living species; only the presence of at least one 

Secondary Wing is universal. M. oregonensis (fig. 12F) and 

M. nivalis (fig. 12C) have an advanced M/1, but usually 

retain simple M\3s; M. oeconomus (fig. 12D) and its extinct 
GENUS MICROTUS 

A 

c 

E 

D 

0 1 2mm 

Figure 12. Microtus. A, Microtus paroperarius, locality CT-2, oldest fauna in the Hansen Bluff faunal sequence, Colorado, Ml 

1 and M\3 of primitive and gigantic form. B, Microtus paroperarius, Cudahy fauna, Kansas, M\3 and Mil of advanced form. C, 

Microtus nivalis, Dzeravaskala fauna, Czechoslovakia, M/1. D, Microtus oeconomus, living, Alaska, Mil and M\3. E, Microtus 

arvalis, living, Belgium, Mil and M\3. F, Microtus oregonensis, living, Washington, M/1 and M\3. 

57 
58 AILOPHAIOMYS AND THE OL YOR SUITE, Y AKUTIA 

namesake, M. paroperarius (fig. 12B) (M. operarius is a junior synonym of M. oeconomus), have a complex M\3, but 

their M/1 often lacks any sign of a buccal Secondary Wing. 

The separation of Lasiopodomys from Microtus identifies an ancestral trunk (at least double) from which the 

branches containing the many species of Microtus diverged, 

but this separation is only useful biochronologically and 

does little to help understand the phylogenetic interrelationships among the species of Microtus. Many attempts, based 

on morphology and genetic analysis (Chaline and Graf, 

1988, among others), have been made to elucidate these 

interrelationships, and some seem obvious from the living 

fauna but biogeographically puzzling: for example, can M. 

oregonensis of the United States be closely related to M. 

nivalis of Europe and western Asia as their simple last upper 

molars would suggest? 

Identijication.-Attempts to define the general configuration of the Anteroconid Complex have resulted in specific, named terms for the major variations in pattern. (See 

van der Meulen, 1973, p. 54-55, for descriptions.) From this 

attempt such terms as "ratticepid," "nivalid," "gregalid," 

"arvalid," "hintonid," and others have originated. The terms 

are useful in description and, as their names indicate, are 

characteristic of the Anteroconid Complex in the majority of 

individuals in particular living species. 

However, the Cap of the Anteroconid Complex is the 

most variable feature in the dentition of microtine rodents, 

and exceptions are common even in the living species, in 

which character polarization would seem to have had the 

greatest time to remove the variability that reflects ancestral 

morphologic features. The various patterns of the Cap of the 

Anteroconid Complex have been considered meaningful in 

species assignment and have been traced backward in time to 

try to establish the history of the living species lineages. This 

concentration on the configuration of the Cap of the Anteroconid Complex has led to neglect of other characters and to 

acceptance of variations in Cap configuration as probable 

evolutionary trends. The results, as published by competent 

authorities, have been extreme in their inferences of differing affinity; particularly in Europe the recognition of only 

one species of Microtus in fossil faunas is rare, and thoughtful population analysis is needed, as has been done by Fejfar 

and Horacek (1983), to recognize potential oversplitting. 

Tracing Cap configuration back in time has caused a 

morphotype from the Karay-Dubina fauna of the Ukraine to 

be assigned to "Microtus ex gr. 'oeconomus"' (Markova, 

1990, fig. 17, nos. 23-34 ). This morpho type is identical to 

forms from the Olyor Suite, Krestovka Sections of Y akutia, 

that, by tracing Cap configurations forward in time, have 

been assigned to "Allophaiomys cf. pliocaenicus" (Zazhigin 

in Sher and others, 1979) or "Allophaiomys pliocaenicus 

(advanced form)" (Zazhigin in Sher, 1986). Specimens of 

the latter populations are frrst illustrated in figures 15 and 16 

of the present report, and are compared with "Microtus ex gr. 

'oeconomus'" from the Karay-Dubina fauna, reproduced 

from Markova (1990), in figure 16. All are called Lasiopodomys spp. in the present report, and they provide no justification for the interpretation that the Krestovka Olyor Suite is 

the same age as the Karay-Dubina fauna on the grounds that 

they both contain the transition from Allophaiomys into 

Microtus-as neither actually does. 

In arriving at these identifications, Markova would 

seem to have considered the lack of a fifth lingual reentrant 

on the first lower molar, always present in Microtus oeconomus, and the presence of a simple last upper molar, never 

found in M. oeconomus, as primitive features of the lineage. 

Zazhigin would seem to have considered the closure of 

Dimension C-C', never found in Allophaiomys pliocaenicus, 

as an advanced feature of the Allophaiomys lineage. Both are 

reasonable assumptions, but neither considered the definitions of other related taxa, and both assumptions extended 

the morphologic definition of the named taxa into the morphology of other taxa as used by others. As a result, what 

Zazhigin called "Allophaiomys pliocaenicus (advanced 

form)" is the same morphotype that Markova referred to 

"Microtus ex gr. 'oeconomus. '" 

The morphotype from Karay-Dubina that Markova 

called Allophaiomys is in agreement with the present report, 

but is not present in the Olyor. The morphotype from the 

Olyor that Zazhigin called Microtus is in agreement with the 

present report, but is not present in the Karay-Dubina fauna. 

As herein defined, three generic morphotypes are recognized: (1) Allophaiomys, represented in the Karay-Dubina 

fauna but not present in the Krestovka fauna; (2) 

Lasiopodomys, called Microtus in the Karay-Dubina by 

Markova and called Allophaiomys in the Krestovka by 

Zazhigin; and (3) Microtus, represented in the Krestovka 

fauna but not present in the Karay-Dubina fauna (but present 

in younger faunas of that region). 

Both authors listed an "Allophaiomys replacement by 

Microtus, " and the age of the Krestovka Olyor fauna was 

based on that of the Karay-Dubina fauna because of this 

replacement. But the "replacement" was not the same, and 

the correlation was incorrect. In the terminology of the 

present report, Lasiopodomys seemed to replace Allophaiomys in the Karay-Dubina fauna, and Microtus seemed to 

replace Lasiopodomys in the Krestovka fauna. 

Actually the few Allophaiomys morphotypes present in 

the Karay-Dubina fauna appear, in Markova's illustrations, 

to be variants of Terricola, and were not replaced by "Microtus." Instead, these morphotypes no longer appeared in the 

younger faunas because they had been polarized out of the 

range of variability in the Terricola populations. Similarly, 

Microtus was an immigrant to the Krestovka fauna, as stated 

in Sher and others (1979), and Lasiopodomys did not 

disappear by evolution into Microtus, but presumably is 

missing in younger faunas because these are not well 

known-younger faunas of the Krestovka Sections are 
GENUS MICROTUS 59 

represented by very small samples (A.V. Sher, oral common., 1990); the genus is known in younger faunas elsewhere in Beringia. In addition, the Krestovka Lasiopodomys 

morphotypes are "typical," and not advanced, they are not 

approaching a Microtus morphotype, as will be discussed in 

this report under the heading, "Age of Krestovka Olyor and 

Cape Deceit faunas." 

Markov a ( 1990) and Sher ( 1986) also assumed that the 

Karay-Dubina fauna was well dated by paleomagnetic control. In reality, no paleomagnetic control exists other than 

that the fauna is older than the Brunhes Chron; the paleomagnetic determinations ended well upsection of the horizon 

from which the described fauna was recovered (V elichko 

and others, 1983). The Karay-Dubina fauna could have lived 

after, during, or before the Jaramillo event. The section overlies Tertiary limestone (Markova, 1990), and the younger 

age constraint provided by the paleomagnetic study is simply 

"older than the beginning of the Brunhes Chron"; how much 

older the Karay-Dubina fauna may be is not constrained. 

Configurations of the Cap of the Anteroconid Complex 

have been used in the hope of subdividing the Arvicolinae 

and in describing variations within their populations. These 

configurations of the Anteroconid Complex are very similar 

in the tribes Microtini and Pitymyini. At times, in the mind 

of the person looking for a pattern, consideration of the general configuration of the Anteroconid Complex supersedes 

the significance of Dimension C--C', the dimension that 

determines whether Triangles 4 and 5 are confluent as in 

Allophaiomys and the Pitymyini or separated as in the 

Microtini. Lineages have been proposed of one Anteroconid 

Complex Cap configuration but include members of both the 

Microtini and the Pitymyini. 

In this regard, workers may tend either to ignore the distinction between Microtus and Pitymys that Hinton (1923) 

specifically described, or to have trouble counting triangles 

forward from the posterior loop of the first lower molar. For 

example, in discussing Microtus paroperarius from the type 

locality, the Cudahy fauna of Kansas, van der Meulen (1978, 

p. 122) stated (bracketed material added in explanation): 

It is possible that Paulson included some five-triangled variants of M. 

meadensis [Terricola meadensis] in his counts [of Microtus paroperarius]. 

This is concluded from the presence of seven five-triangled M. meadensis 

variants in vial V40299 (evidently picked forM. paroperarius). M. meadensis is distinguished from M. paroperarius by the better developed anterior 

loop [Cap] of the former. On this criterion theM. paroperarius ml'sofPaulson (1961: Figs. [7]F and [7]0) belong toM. meadensis. Neither Hibbard 

(1944) nor Paulson (1961) have described five-triangled variants of M. 

meadensis. 

In the definitions by Hinton (1923) for Microtus, given 

previously (p.44), and for Pitymys, given later (p. 65), which 

were certainly followed by Hibbard and Paulson, Terricola 

meadensis is a species of the tribe Pitymyini and cannot 

have a five-triangled variant, or even a four-triangled variant; if it did it would be a member of the tribe Microtini. 

Dimension C--C', as well as Dimension B-B', must be closed 

to have either or both Triangles 4 and 5; and the specimen 

with these character states belongs in the tribe Microtini by 

definition. Members of the tribe Pitymyini have confluent 

Primary Wings in the position of Triangles 4 and 5. 

Paulson's figures 7F and G show specimens in which 

the Primary Wings are separated by closure of Dimension 

C--C'; they are Microtus, as he indicated. Van der Meulen 

(1978) apparently forgot the difference between Microtus 

and Pitymys in his concern about the configuration of the 

Cap of the Anteroconid Complex; if he were considering the 

definitions of Hinton (1923), he could not have made these 

statements. 

Paulson's figures 7F and G of Microtus paroperarius 

do have confluent Triangles 6 and 7 (Secondary Wings). 

These confluent Secondary Wings on the Cap of the Anteroconid Complex are well developed. Both the Microtini and 

the Pitymyini may have completely confluent Secondary 

Wings; it is the nature of the Primary Wings that separates 

the members of these two tribes (fig. 1 0). Because of the 

nature of the Secondary Wings on Paulson's figures, it 

seems plausible that van der Meulen assigned these specimens to Pitymys meadensis; that is, it seems possible that 

van der Meulen mistook confluent Triangles 6 and 7 for confluent Triangles 4 and 5 in these two specimens. The diagnostic Primary Wings (Triangles 5 and 6) are, however, not 

confluent, and the specimens are Microtus. 

Van der Meulen (1978) did not explain how he defined 

Microtus and Pitymys (= Terricola): a strange situation in a 

paper naming new species of these genera. Paulson's figures 

7F and 7G are Microtus paroperarius by the only available 

definition: Dimension C--C', between Triangles 4 and 5, is 

closed. If one can count to Triangle 4, no similarity exists 

between these two specimens and Terricola meadensis. 

Seldom is a late Pleistocene fauna described with only 

one species of Microtus or Terricola; the reason possibly lies 

more in the variability of the pattern of the Cap of the 

Anteroconid Complex, than in the congeniality of species of 

these genera. If any success results from consideration of the 

configuration of the Cap of the Anteroconid Complex, it will 

be on a statistical basis, as was accomplished by Fejfar and 

Horacek (1983). At present, no pattern is apparent other than 

the characters discussed herein. 

Correlation.-In the Anza-Borrego Desert of California, Microtus californicus is presumably dated at about 1.4 

million years old (locality 21, fig. 1; fig. lOA; ANZA-1 of 

fig. 14). The locality, LACM 6683, is 109m above the Olduvai event and 360 m below the Brunhes Chron, but the rate 

of sedimentation was not constant. As discussed previously 

(p. 50) in the section on Lasiopodomys from the AnzaBorrego Desert, the date is approximate. The presence of 

Terricola meadensis in overlying deposits (fig. 14, Locality 

ANZA-3) suggests that the youngest normal polarity 

recorded represents the Brunhes Chron, rather than the 

Jaramillo event as inferred by those making the paleomagnetic study (Johnson and others, 1984), because Terricola 
60 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

does not appear elsewhere in the United States until after 

the Jaramillo event, both east and west of the Rocky Mountains (Repenning, 1983). 

The specimens of Microtus from the Anza-Borrego 

Desert are the oldest dated record of the genus in the world, 

but the date is not consistent with the remainder of the 

history of Microtus; it seems too old (see fig. 14). If the 

beginning of the Brunhes is represented, as seems evident, 

the Jaramillo appears to be missing in the section, and possibly reversely polarized deposits older and (or) younger than 

the Jaramillo are also missing. If so, the age is quite uncertain. The association with several Blancan holdover microtines (Mictomys vetus, Mimomys parvus, and Ondatra 

idahoensis: Zakrzewski, 1972; Repenning, unpub. data) 

does suggest a rather early age following the Olduvai event, 

possibly as much as 1.4 million years ago, and still the oldest 

known Microtus in the world. 

However, great age for an advanced Microtus morphotype indicated by the Anza-Borrego record is also indicated 

by the younger, and larger, sample from the Irvington fauna 

of central California (Savage, 1951). The age of the Irvington fauna is plausible in consideration of global records of 

the genus (figs. 10C, 14). 

The record from the Irvington fauna includes 14 first 

lower molars and 5 last upper molars that indicate the presence of the advanced species Microtus califomicus, with a 

morphologic variability that had polarized to a fixed, littlevariable phenotype. Such an advanced morphotype did not 

become common east of the Rocky Mountains until the 

610,000-year-old M. paroperarius of the Cudahy fauna of 

Kansas, and it is not apparent that M. paroperarius evolved 

a morphologically stable pattern before its extinction about 

450,000 years ago. Yet the Irvington fauna of California is in 

reversely polarized deposits, clearly more than 790,000 

years old. 

As discussed previously (p. 50), the first Lasiopodomys known in the United States, also from the AnzaBorrego Desert (fig. 11A), is at least 1.2 million years old if 

the youngest normal polarity represents the Jaramillo event; 

and as discussed, if the youngest deposits with normal polarity represent the Brunhes, the record seems to be older. However, Lasiopodomys did not immigrate from Beringia to the 

area east of the Rocky Mountains until 850,000 years ago, 

and immigrant Microtus did not appear there until about 

450,000 years ago. To the east of these mountains, Microtus 

reached southern Canada possibly 875,000 years ago in the 

Wellsch Valley fauna, as discussed, and its oldest record east 

of the mountains in the United States is approximated at 

450,000 years ago in the Porcupine Cave fauna of Colorado 

(Bamosky and Rasmussen, 1988). 

The evolution of Microtus paroperarius out of 

Lasiopodomys in the United States east of the Rocky Mountains is obviously a provincial event and does not correlate 

with dispersal patterns. Evidently, Lasiopodomys and 

Microtus (other than M. paroperarius) dispersed across 

Beringia to western North America between 1.4 and 1.2 

million years ago, but the later dispersal of these microtines 

southward was at different times and followed different 

routes on either side of the Rocky Mountains (Repenning, 

1990). 

Allophaiomys is not known west of the Rocky Mountains, but it immigrated to the eastern three-quarters of the 

United States at the beginning of the Olduvai event. No data 

from the west suggest an immigration of any micro tine at the 

beginning of the Olduvai event, but the genus Phenacomys 

dispersed south to Idaho (Froman Ferry, locality 33, fig. 1; 

Repenning, unpub. data) after the Olduvai event. The lack of 

Allophaiomys west of the mountains thus suggests that the 

genus was present in Beringia only during the Olduvai and 

that it was not present to participate in a southward dispersal 

west of the Rocky Mountains with Phenacomys. No paleomagnetic evidence exists in Beringia that suggests nonmarine deposition during the Olduvai event, so the suggestion 

cannot be supported by Beringian fossil records. 

Later, 850,000 years ago, Terricola and Lasiopodomys 

entered the United States east of the Rocky Mountains. 

Lasiopodomys was by then a long-time resident of Beringia, 

but the lack of record ofTerricola in Beringia again suggests 

that this genus had a very brief presence in this northern 

region after the Jaramillo event and before the Brunhes 

Chron. In this case, Beringian deposits believed to be of this 

age do exist, in the type section of the Olyor Suite ofYakutia 

(Virina and others, 1984), but Terricola is not reported from 

their faunas, which are represented by small samples. 

Beringian Microtus is first recorded before the 

Jaramillo event (p. 84); the genus is abundant in Yukon 

Territory (eastern Beringia) during the Jaramillo event 

(p. 54); it is present in southern Canada before the Brunhes Chron (p. 36); and it frrst appears, as an immigrant, 

in the United States east of the Rocky Mountains during 

the middle part of the Brunhes Chron (=450,000 years 

ago; Bamosky and Rasmussen, 1988). 

These records of the distribution of Allophaiomys, 

Terricola, and Microtus suggest major ecological restrictions in the dispersal of these microtines through Beringia 

and to the south. Constraints on the use of a dispersal route 

to the west of the Rocky Mountains are, in part, related to 

uplift and erosion of coastal mountains in Canada and 

Alaska and to periods of intense glaciation in these mountains. Constraints on the use of a dispersal route to the east 

of the Rocky Mountains are only partially documented; these 

include subtropical climates in the Great Plains of the United 

States, forests in the Great Plains of Canada, and possibly 

continental ice before 2.0 million years ago and intermittently after 850,000 years ago (Repenning, 1990; Repenning 

and Brouwers, 1992). 

The delay in southward dispersal of Microtus into eastem U.S.A. seems to follow climatic deterioration and 

requires that the provincial nature of latitudinal climatic 

zones, as well as east-west regional separation of microtine 
GENUS MICROTUS 61 

faunas by the Rocky Mountains, be considered in biochronologies. Correlations in North America based on the genus 

Microtus must be specific for at least four different regions: 

Beringian, Canadian, Eastern U.S.A., and Western U.S.A. It 

seems reasonable that a fifth, Mexican, region will be added 

when enough information is available. 

These regional considerations are well illustrated by 

Microtus, but apply to most microtines. The regions of Eurasia are not well comprehended from this biohistorical point 

of view, but separate faunal regions and provinces would 

seem to be more numerous there than in North America. 

These are not yet well documented by differences in the distribution and composition of microtine faunas, although 

broad differences between Europe, western Asia, and eastern 

Asia are presently recognizable. As indicated in this discussion, there is ample reason to infer the presence of northeastem (Beringian) and southeastern (Oriental) Asian regions. 

MICRO'IT.JS FROM THE HANSEN BLUFF FAUNAS 

(fig. 12A; locality 15, fig. 1) 

Hansen Bluff is in the broad valley of the Rio Grande of 

southern Colorado, U.S.A., a few miles north of the New 

Mexico State line in the eastern part of the Rocky Mountains. The bluff is at 7,546 feet (2,300 m) elevation; 1,400 

feet (428 m) lower than, and about 39 miles (63 km) northeast of SAM Cave, New Mexico. Both localities are within 

deposits filling the uppermost basin of the Rio Grande. 

Hansen Bluff contains a succession of vertebrate and invertebrate faunas and pollen floras that range in age from possibly 840,000 to an approximated 700,000 years (Rogers and 

others, 1985). 

Age control for most of the Hansen Bluff faunas is 

tightly constrained by paleomagnetic patterns, one identified 

tephra of known age, and climatic correlation with the early 

part of the Nebraskan glaciation of North America (Rogers 

and others, 1985). Rogers confmned its position within the 

youngest reversed deposits of the Matuyama Chron after 

1985 by digging to the Jaramillo event at the foot of Hansen 

Bluff, and by drilling a core through the Matuyama Chron to 

the Gauss Normal-polarity Chron at the same location (K.L. 

Rogers, oral common._, 1986; and Rogers and others, 1992). 

The faunal sequence was listed as "Alamosa, Colorado" in 

Repenning (1987), which was written earlier than Rogers 

and others (1985). 

The oldest faunas of the Hansen Bluff faunal sequence 

(localities CT1-3 and PP2) are about 820,000 years old. The 

youngest (CG, TS, and Ff) are estimated to be about 

700,000 years old (Rogers and others, 1985). 

The microtine fauna includes Microtus paroperarius 

(fig. 12A) and Terricola meadensis (fig. 13G; listed as Pitymys meadensis in Rogers and others, 1985). T. meadensis 

represents the immigrant group of the Pitymyini in North 

America (the "quasiater species group" of Repenning, 

1983), and Hansen Bluff is the oldest record of this 

immigrant in North America. This species varies little from 

the oldest to the youngest faunas in Hansen Bluff (Rogers 

and others, 1985): its morphotype seems to have polarized, 

and it had not recently evolved from some more primitive 

ancestor like Terricola arvaloides of Eurasia. Dimension 

A-A', however, is not as markedly constricted as it is in the 

type sample from the 610,000 year-old Cudahy fauna of 

Kansas. 

In contrast, Microtus paroperarius varies from the oldest to the youngest Hansen Bluff faunas in the shortening of 

Dimension A-A' and complication of the last upper molar. 

Its changing mode of variability indicates a recent evolution 

out of Lasiopodomys by its lack of polarization in dental pattern. Although no Lasiopodomys morphotypes are present, 

the oldest populations of Microtus paroperarius in the 

Hansen Bluff sequence have a relatively simple Anteroconid 

Complex on the first lower molar with little reduction of 

Dimension A-A', and a fairly high proportion (40 percent) 

of simple last upper molars (fig. 12A). 

These oldest faunas of the Hansen Bluff faunal 

sequence contain the only known association of upper and 

lower dentition of Microtus paroperarius. In this specimen a 

simple first lower molar is associated with a simple last 

upper molar, indicating that some of the simple last upper 

molars in the fauna belong to primitive Microtus, rather than 

all of them belonging to the pitymyinine Terricola. Relative 

proportions, based upon the count oflower first molars, suggest that 40 percent of M. paroperarius individuals in the 

oldest fauna of Hansen Bluff had a simple last upper molar. 

Simple last upper molars are unknown from the younger faunas of the Hansen Bluff sequence, and some of the first lower 

molars show well-developed reentrants anterior to the Secondary Wings and a conspicuous reduction of Dimension AA'. 

Microtus paroperarius from the older faunas of Hansen 

Bluff closely resembles: (1) Microtus variants of Lasiopodomys deceitensis from the Cheetah Room fauna (see 

Repenning and Grady, 1988, fig. 4); (2) Microtus morphotypes (primitive) in the population referred to as Microtus 

paroperarius-Lasiopodomys deceitensis from Cumberland 

Cave (see van der Meulen, 1978, fig. 11D, F); (3) the more 

primitive forms of Microtus paroperarius shown by Pfaff 

(1990; fig. 4 except 4D and G) from the Trout Cave No. 2 

fauna in West Virginia; and ( 4) the simplest forms from the 

type population of M. paroperarius from the Cudahy fauna 

(see Paulson, 1961, fig. 7A-D). They do not resemble the 

Lemmiscus morphotypes found in the nearby but older population of Allophaiomys from SAM Cave (this report, fig. 

6F,G). 

The population described by Pfaff (1990; fig. 4) from 

Trout Cave No. 2 most resembles samples from the middle 

part of the Hansen Bluff sequence, but sample sizes from this 

part of the Hansen Bluff sequence are very small. In the 

youngest faunas from Hansen Bluff, approximated at 
62 AUOPHAIOMYS AND THE OLYOR SUITE, Y AKUTIA 

700,000 years old by the rate of deposition calculated in the 

lower part of the section (where age control is stronger), the 

populations of Microtus paroperarius are comparable to the 

typical form from the Cudahy fauna of Kansas (Paulson, 

1961 ), but again are represented by very small sample sizes. 

Although not far from the SAM Cave localities and in 

deposits filling the same valley, the Hansen Bluff faunal 

sequence contains no record of Allophaiomys. It has been 

noted previously in the discussion of Allophaiomys (p. 31) 

that in the core drilled at the foot of Hansen Bluff a single 

tooth that can only be attributed to Allophaiomys was 

collected 240 feet down core, very close to the base of the 

Olduvai event. A few teeth of Allophaiomys were also 

recovered higher in the core, above the Olduvai event. That 

the genus was probably a part of the local fauna until shortly 

after the Jaramillo event is indicated by the faunas from 

nearby SAM Cave, containing large samples. 

It would appear that Allophaiomys became extinct in 

the upper part of the Rio Grande drainage basin shortly 

before 820,000 years ago. No records in the United States 

suggest that it survived later, although the Allophaiomys 

morphotype survives in the living fauna as a variation of 

Pedomys at lower elevations east of the Rocky Mountains. 

There is a global pattern of province-by-province extirpation of Allophaiomys soon after the appearance of 

Lasiopodomys, or Microtus where the more primitive intermediate genus is not known. The pattern, repeated in many 

records throughout the Northern Hemisphere (Repenning, 

1990), appears to reflect climatic change to an environment 

too cold for Allophaiomys but preferred by Microtus, or 

Lasiopodomys, as will be discussed. The pattern also suggests that the evolution of Allophaiomys into Pedomys in 

North America provided some advantage, as Pedomys persists in the presence of Microtus, but usually only in the more 

temperate parts of colder environments; its avoidance of 

higher elevations in the Rocky Mountains and of summer 

arctic air in northeastern North America is conspicuous in its 

modem distribution. 

Possibly because of differing environmental constraints, no Pedomys are known from the high-elevation 

Hansen Bluff faunal sequence or the Porcupine Cave fauna 

farther north and at greater elevation in Colorado. Pedomys 

was, and is, widely distributed across the Great Plains; and 

the genus now lives westward to the eastern foot of the 

Rocky Mountains up to 5,000 to 7,000 feet (1,542-2,158 m) 

in elevation. It is not known in higher terrain. It seems possible that the 7,546-foot elevation of Hansen Bluff in the 

upper Rio Grande Valley has always been too high for this 

genus. Although Pitymys cumberlandensis is known from 

the Appalachian Mountains before the time of the Hansen 

Bluff faunas, the genus appears to have always remained distributed only in the eastern United States. Terricola did not 

enter this eastern province, although present in both high elevation localities, Hansen Bluff and Porcupine Cave, suggesting some reason other than high-elevation climate factors for 

its avoidance of the eastern United States. 

The absence of both Allophaiomys and Lasiopodomys, 

and the transition upsection into typical Microtus paroperarius make the 820,000-year-old oldest faunas of Hansen Bluff 

appear younger than the Cumberland Cave fauna of Maryland, which is, accordingly, considered as being about 

830,000 years old and intermediate in age between the Cheetah Room fauna (containing no Microtus) and the Hansen 

Bluff fauna (containing no Allophaiomys or Lasiopodomys) 

(fig. 14). 

MICR01T.JS FROM THE CUMBERLAND CAVE AND 

LOCALI1Y CRH-47 FAUNAS 

(localities 11 and 25, fig. 1) 

The Cumberland Cave fauna of western Maryland has 

been discussed in connection with its Allophaiomys and 

Lasiopodomys. Locality CRH-47 fauna of easternmost 

Beringia in northern Yukon Territory, Canada, has been discussed in connection with the age of Microtus andAllophaiomys from the Wellsch Valley fauna of Saskatchewan and in 

connection with Lasiopodomys from CRH-47. 

As just mentioned, Cumberland Cave seems to be about 

830,000 years old. Locality CRH-47 was deposited during 

the Jaramillo polarity event between 970,000 and 900,000 

years ago. Two younger localities in the Old Crow basin of 

Yukon Territory, CRH-11 and CRH-64, also contain 

Lasiopodomys and are normally magnetized (Morlan, 1984 ), 

suggesting that they also represent the Jaramillo event and 

that the fauna from CRH-47 may have lived fairly early during this event. This assumption is based upon the further 

assumption that Lasiopodomys became extinct in eastern 

Beringia before the Brunhes as it did in the United States and 

western Beringia. 

Because of their latitudinal provinciality, the faunas of 

Cumberland Cave and Locality CRH-47 contrast greatly, 

even though they may be only 70,000 years different in age. 

In a single, intergrading population identified as Microtus 

paroperarius-Lasiopodomys deceitensis, Cumberland Cave 

contains both L. deceitensis and primitive M. paroperarius 

morphotypes. The species M. paroperarius evolved out of 

Lasiopodomys in the Cumberland Cave fauna. 

The older Locality CRH-47 also contains Lasiopodomys deceitensis, but this fauna contains a large spectrum 

of Microtus morphotypes including forms resembling primitive M. paroperarius as well as forms that appear related to 

modem species (R.E. Morlan, oral common., 1986-1987 and 

work in progress, 1991). Allophaiomys is present in the 

Cumberland Cave fauna but missing in the fauna of Locality 

CRH-47. No pitymyinines are present in Locality CRH-47, 

although they are abundant in Cumberland Cave. The effects 

of latitudinal provincialism are obviously great at this time, 

just prior to and during the Nebraskan glaciations (beginning 

850,000 years ago). 
GENUS MICROTUS 63 

Between the ages of these two faunas, about 850,000 

years ago, the genera Lasiopodomys and Terricola dispersed 

southward from Beringia into the conterminous United 

States, as has been mentioned (p. 33). The complete lack of 

any Terricola in Locality CRH-47, or in other locality along 

the Old Crow River (Morlan, 1984 ), suggests that it was after 

the Jaramillo event that Terricola passed through Beringia 

on its way to the United States, in agreement with its earliest 

records in the U.S.A. 

The original date for this dispersal was assumed to 

approximate the frrst of the Nebraskan glacial advances in 

North America, the age of which was first inferred from the 

age of stage 22 of the oceanic oxygen isotope record (Repenning, 1984). Most recognized microtine dispersal events can 

be associated with "cold" climatic events as suggested by the 

oxygen isotope record (Repenning and others, 1990). 

Since that initial evaluation of the age of this dispersal 

event, the age of the Cumberland Cave fauna (about 830,000 

years) and that of the older Cheetah Room fauna of West 

Virginia (about 840,000 years), both containing some of the 

immigrants, have reinforced the younger limit of this 

assumption. Among the SAM Cave faunas of New Mexico, 

Locality BOT -4 contains none of the immigrants but is 

younger than the Jaramillo Normal-polarity Subchron 

(younger than 900,000 years), supporting and further 

restricting the older limit of the assumption made from oxygen stage 22 and the Nebraskan glaciations. The author still 

considers as reasonable the interpretation, originally based 

on the inferred age of oxygen stage 22, that the dispersal of 

these microtines into the United States was about 850,000 

years ago. 

After this dispersal event, records east of the Rocky 

Mountains in the United States show Lasiopodomys evolving only into Microtus paroperarius; no other species of 

Microtus is evident until the next dispersal event, about 

450,000 years ago, and these are of immigrants from Beringia, and presumably Asia. Despite evidence of much earlier 

(about 1.4 Ma) immigrant populations west of the Rocky 

Mountains, despite the great variety of Microtus morphotypes in Yukon Territory (co-occurring with Lasiopodomys 

before 0.97 Ma), and despite the southern Saskatchewan 

record (perhaps 0.87 Ma) of an advanced morphotype of 

Microtus from reversed deposits of the Wellsch Valley fauna 

(co-occurring with Allophaiomys), it seems that east of the 

Rocky Mountains Microtus did not enter the United States 

until about 0.45 million years ago, 1 million years after it 

was first present along the Pacific Coast of the United States 

(Repenning, 1984, 1987, and 1990). 

These later immigrant Microtus are assigned to living 

species. M. paroperarius appears to have become extinct 

shortly after this late Microtus invasion; only in Porcupine 

Cave of south-central Colorado isM. paroperarius found in 

association with more advanced species of Microtus that 

were then newly immigrant from Beringia (Bamosky and 

Rasmussen, 1988). 

These different but interrelated records have direct 

bearing on the age of Microtus in Beringia and the Olyor 

Suite of the Krestovka Sections. During the Jaramillo 

Normal-polarity Subchron, Microtus was abundant and 

diverse in Beringia, but unknown in the United States except 

west of the Rocky Mountains. In the discussion of the 

Wellsch Valley fauna of southern Saskatchewan, Canada, it 

was indicated that Beringian Microtus had a range that 

extended essentially to the northern boundary of the United 

States before 850,000 years ago; no record indicates that it 

moved southward across this international boundary to the 

east of the Rocky Mountains until about 450,000 years ago, 

although it has a record west of these mountains perhaps 1.4 

million years old. The oldest record of Microtus to the east 

of the Rocky Mountains is in Cumberland Cave, Maryland, 

and is clearly the result of endemic evolution out of 

Lasiopodomys in the United States. 

MICR01US FROM THE TROUT CAVE NO. 2 FAUNA 

(locality 17, fig. 1) 

Trout Cave is in West Virginia, near Hamilton Cave, 

which contains the Cheetah Room fauna. The microtines 

from locality Trout Cave No. 2 were recently described by 

Pfaff (1990) and include Microtus paroperarius, Pedomys 

llanensis, and Pitymys cumberlandensis. The frrst two 

species were described as being more advanced than from 

Cumberland Cave, the last as being the same. 

As indicated previously, the population characteristics 

of Microtus paroperarius from Trout Cave appear to fit in 

the upper part of the Hansen Bluff faunal sequence, probably 

correlative to the earliest part of the Brunhes Chron. No 

Lasiopodomys morphotypes are present, as there are in Cumberland Cave, and no simple last upper molars were assigned 

to M. paroperarius, as in the oldest faunas of Hansen Bluff. 

First lower molars from Trout Cave No. 2 include primitive 

forms like those from the oldest Hansen Bluff faunas as well 

as more advanced forms, but none are as advanced as are 

some from the type locality, the Cudahy fauna of Kansas 

(Paulson, 1961). 

A conspicuous reduction of Dimension A-A' seems 

indicated by Pfaffs figures 4D and G and may approximately correlate with his statement that 39 percent of the 

sample had cementum in buccal reentrant angle 4, the buccal 

side of this Dimension. Cementum is increasingly likely to 

be deposited in the reentrants as they become deeper transversely. Pfaff noted that cementum deposition is greater than 

that in the Cumberland Cave fauna and less than that in the 

type Cudahy fauna. The presence of such cement deposition 

indicates a stage of advancement beyond that of the oldest 

faunas of Hansen Bluff, as do the morphologies that Pfaff 

illustrated. 

Pfaff also noted that Pedomys llanensis is more 

advanced than Allophaiomys guildayi from the Cumberland 
64 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Cave fauna, but still retains a wide range of individual variation, with a good percentage (34 percent) of Allophaiomys 

morphotypes (having no Dimension A-A'; Pfaffs figs. 5C, 

D, and E). In this respect the population may be less 

advanced than the type sample from the Cudahy fauna of 

Kansas, which is extremely small; it is clearly advanced over 

the condition of Allophaiomys guildayi from Cumberland 

Cave. 

The population characteristics of Pitymys cumberlandensis from Trout Cave No. 2 are very similar to those of 

Cumberland Cave and Hanover Quarry Fissure. Again, these 

similarities suggest a persistence of the polarization of characters in this lineage. From its evolution out of Allophaiomys 

in the Cheetah Room fauna (about 840,000 years old) 

through Hanover Quarry Fissure (perhaps 835,000 years), 

Cumberland Cave (about 830,000 years), Trout Cave No.2 

(possibly 725,000 years), and possibly lasting until the living 

fauna, Pitymys pinetorum shows no change in the morphologic structure of its teeth other than in enamel-thickness 

differentiation (van der Meulen, 1978). 

Although the opinion is based upon inadequate faunal 

samples from the upper part of the Hansen Bluff faunal 

sequence, it seems that Trout Cave No. 2 may be somewhat 

greater than 700,000 years old, but clearly younger than 

820,000 years old, by comparison with this series of faunas. 

In agreement with Pfaff, it certainly seems older than the 

610,000-year-old Cudahy fauna of Kansas. An arbitrary age 

of about 725,000 years is assigned. 

GENUS LEMMISCUS THOMAS, 1912 

(fig. 6F, G, and J; Mt. Magruder, Nevada; locality 37, fig. 1) 

Type species.-Arvicola curtatus Cope, 1868. 

Revised dental diagnosis.-A genus of the tribe 

Microtini with only the buccal Secondary Wing strongly 

developed on the Anteroconid Complex of the first lower 

molar; a weak lingual Secondary Wing may be present or 

absent; because of this arrangement of the cusps of the first 

lower molar, the Primary Wings (forming fully developed 

Triangles 4 and 5) are in a position more alternating than 

opposing, as is usual in the Microtini; the last upper molar 

has two alternating triangles and an elongate, uncomplicated 

posterior loop. 

"TYPICAL .. LEMMISCUS 

Revised dental diagnosis.-As for the genus. 

Comments.-Lemmiscus is a North American genus 

(largely U.S.A.) of the tribe Microtini. The genus now lives 

in the northwestern Great Plains of the United States 

(extending north a short distance into Canada) and in the 

northern Rocky Mountains. West of these mountains the 

range of Lemmiscus extends southward to the Inyo Mountains of California and down the Wasatch Plateau to 

Escalante, Utah; this far south it lives at much higher elevations (9,000 to 10,000 ft; 2,776-3,048 m). 

The single species, Lemmiscus curtatus, has always 

been questionably considered a member of genus Lagurus, 

of tribe Lagurini, because of many similarities, but differences have been noted (see Carroll and Genoways, 1980). 

These differences have led to the separation of the American 

species from Eurasian ones by including Lagurus curtatus in 

a subgenus Lemmiscus. Lemmiscus is sometimes treated as a 

full genus within the tribe Lagurini; this is the frrst published 

treatment as a member of the tribe Microtini. 

The direct origin of Lemmiscus curtatus out of North 

American Allophaiomys, discussed previously in connection 

withAllophaiomys from SAM Cave, New Mexico (p. 33-35; 

fig. 6F, G, and J), requires a separate generic, non-lagurinine 

identity for this lineage. It belongs in the tribe Microtini, and 

Thomas' term is here treated as a full genus within the tribe. 

The relationship with Allophaiomys will be further considered when the several faunas of SAM Cave are completely 

studied, but the relationship seems obvious in the sample 

from Locality BOT -4 of SAM Cave. 

R.E. Morlan (written common., 1991) has identified an 

apparently true lagurinine (more like living Eolagurus than 

Lagurus) from Locality CRH-47 in the Old Crow basin of 

Yukon Territory, Canada. Otherwise the tribe Lagurini 

seems not to have entered North America. Although SAM 

Cave, New Mexico, and Porcupine Cave, Colorado (containing the living species Lemmiscus curtatus; Bamosky and 

Rasmussen, 1988), are both well south of the modem distribution of L. curtatus, this is not the southernmost extent of 

its former range. Harris (1980) reported the species from Dry 

Cave, southeastern New Mexico, dating from a late Pleistocene glacial period. 

This single-species lineage (ignoring the possibility 

that the material from SAM Cave may deserve a separate 

species name) has no bearing on the age of the Olyor Suite 

in the Krestovka Sections. The North American lineage differs from Old World lagurinines by the dominance of only 

the buccal Secondary Wing on the frrst lower molar, by only 

two alternating triangles between the anterior and posterior 

loops of the last upper molar, and by having cementum 

present in the reentrants angles of the teeth. Other differences have been noted by Davis (1939). 

The morpho types from SAM Cave, Locality BOT -4, 

differ from living Lemmiscus curtatus in having relatively 

wide Dimensions B-B' and A-A', more strongly resembling 

Allophaiomys. However, by about 450,000 years ago these 

dimensions have been reduced to the condition observed in 

the living species, L. curtatus, as documented in Porcupine 

Cave, Colorado (Barnosky and Rasmussen, 1988). The 

genus is unusual in that it appears to have originated in and 

not dispersed far from the Rocky Mountains. Hypothetically, 

its origin may have resulted because of high-elevation cooling before the Nebraskan glaciation, and out of subtropical 

to temperate Allophaiomys. Its present northward range 
GENUS PROEDROMYS 65 

retraction seems to be the result of post-glacial hot summers, 

of which it is intolerant. The modern northward range limit, 

essentially to the northern border of the United States, also 

suggests an intolerance of severe winter cold, and that the 

Mictomys and ?Phenacomys association in SAM Cave indicates a similar ecologic restriction to cool summers and 

relatively temperate winters. 

Rogers and others ( 1985) recorded a relatively warm 

climate at nearby Hansen Bluff, Colorado, just before the 

time of the second advance of the Nebraskan ice in the 

United States, and Lemmiscus was not present in this fauna. 

Interestingly, a few specimens of Mictomys kansasensis 

were in this fauna, but these were all badly abraded, as 

though they had washed down into the valley of the Rio 

Grande from the surrounding mountains. Possibly coolsummer-, warm-winter-adapted Lemmiscus was first forced 

to withdraw northward (by virtue of its evolved adaptations) 

not long after it evolved out of the local population of subtropical to temperate Allophaiomys. 

GENUS PROEDROMYS THOMAS, 1911 

(Minchow, Kansu, People's Republic of China; locality 36, fig. 1) 

Type species.-Proedromys bedfordi Thomas, 1911. 

Revised dental diagnosis.-A genus of the tribe Microtini with a first lower molar like that of "typical" 

Lasiopodomys, having a closed Dimension C-C' and a 

rounded Cap with no Dimension A-A' or Secondary Wings; 

but with a last upper molar having the posterior loop reduced 

to a single buccal Hook (illustrated in Repenning and Grady, 

1988; fig. 4A). 

"''YPICAL" PROEDROMYS 

Revised dental diagnosis.-As for the genus. 

Comments.-Proedromys is a Chinese genus of the 

tribe Microtini and has little or no distribution outside of that 

faunal region. Like Microtus, its fossil record goes back to 

before the Jaramillo event (Gongwangling fauna; An and 

Ho, 1989). The first lower molar appears identical to that of 

Lasiopodomys deceitensis, and an origin out of Allophaiomys or early Lasiopodomys seems apparent but is not as yet 

documented. 

The genus is characterized by a reduction, rather than 

complication, of the last upper molar; the posterior loop is 

essentially lost even in its oldest recognized form, from the 

Gongwangling fauna of China (Zheng and Li, 1990). The 

genus shows little change to the living fauna and has no evident bearing on the age of the Olyor Suite of Y akutia. The 

unusual evolutionary vector of reduction, rather than complication, of the third upper molar has only been observed 

elsewhere in living Phaiomys leucurus (fig. 4), and in Phaiomys it has progressed only half as far in that direction. 

TRIBE PI1YMYINI, REPENNING, 1983 

Basis ofdiagnosis.-Hinton, 1923 (for genus Pitymys): 

"M1 with posterior loop, followed successively by three substantially closed and alternating triangles and a confluent 

pair of triangles, and terminated by an anterior loop of variable form." 

Revised dental diagnosis.-Genera of the tribe Pitymyini (subfamily Arvicolinae) have dentinal confluence 

between the Primary Wings of the Anteroconid Complex 

(Dimension C-C' open or substantially open); Cap of the 

Anteroconid Complex is complex (Secondary Wing or 

Wings present, Dimension A-A' present and variously 

reduced); Dimension B-B' often narrowed or closed; cheek 

teeth rootless with cement in the reentrants. 

Generic contents of the tribe.-Herpetomys*, Terricola, Neodon*, Orithriomys*, Pedomys, Pitymys, and 

Tyrrhenicola*. 

[Note: The genera marked by an asterisk have not been 

examined in detail during this study and no opinions are 

offered. They have no bearing on the age of the Olyor Suite.] 

Discussion.-In the tribe Pitymyini the Anteroconid 

Complex Dimension C-C', between the Primary Wings of 

first lower molar, does not shorten and separate the two 

Primary Wings as in the Microtini; it remains as it was in 

Allophaiomys, and the Primary Wings (incomplete Triangles 

4 and 5) remain partially to completely confluent. Narrowing 

of Dimension A-A', to initiate the development of Secondary Wings on the Cap of the Anteroconid Complex, is the 

only criterion that separates all species of the tribe Pitymyini 

fromAllophaiomys. Hinton's diagnosis of Pitymys separates 

it from Microtus, but not from Allophaiomys, which was not 

known in 1923, although the very similar Phaiomys was and 

has been considered a pitymyinine. 

The interrelationships of tribe Pitymyini are as complex 

as those of tribe Microtini, and are in need of as much study. 

In North America the tribe is represented by two lineages. 

One is endemic and contains the type species of Pitymys as 

well as the genus Pedomys. The other is that of Terricola, 

and this lineage immigrated to North America from Asia 

850,000 years ago (Repenning, 1983), with Lasiopodomys 

of the tribe Microtini. 

Rather than become involved in a major revision of 

nomenclature, Repenning (1983) called the two lineages 

"species groups," each named after representative living 

North American species: the "pinetorum species group" for 

the native stock and the "quasiater species group" for the 

immigrants from Eurasia. 

Ognev (1950) has discussed the problem of generic separation of the Eurasian species-the "quasiater species 

group"-from the separately derived Pitymys of North 

America-the "pinetorum species group" (he did not discuss 

the concept of these groups). He stated that Terricola Patio 

(1867) was preoccupied by Terricola Fleming (1828), said 

to be a genus of mollusk. He suggested (Ognev, 1950, p. 345 
66 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

of the English translation) that "it would be most reasonable 

to unite all Old World animals within the confines of the subgeneric name Micrurus to distinguish them from the American Pitymys s. str." His use of Micrurus as a subgenus 

reflects his inclusion of all genera of the Pitymyini and the 

Microtini in the genus Microtus. 

Ognev (1950), however, did not recognize this taxonomic separation of the Old World forms included in Pitymys (although he did so in his classification of 1948), but 

continued using the genus Pitymys in the U.S.S.R. His suggested (1950) and substituted (1948) generic name was 

Micrurus Forsyth-Major (1877), a pitymyinine genus 

erected to hold a species from Sicily. Micrurus ForsythMajor is preoccupied by Micrurus Wagler (1824), a coral 

snake. In addition, Ognev's statement that Terricola Patio 

was preoccupied was in error; Fleming (1828) used the term 

''Terricola" in the Latin vernacular for land-dwelling mollusks as a group, and not as a genus. It, therefore, is available 

as a generic name (Chaline and others, 1988; K. Kowalski, 

written common., 1991). 

Terricola Patio (1867) is the first available name and 

was originally applied as a subgenus to include both Terricola savii and Terricola subterraneus where their ranges 

overlap in Switzerland. There appears to be considerable 

variability in the development of the last upper molar in species of Terricola, which needs further study to explain. 

Although many have, for many years, suggested that 

the two groups of Pitymyini should be separated, Chaline 

and others (1988) were the first to do so. There seems to be 

no reason for not doing so except for the reluctance to drastically revise the present nomenclature. With this separation 

the genus Pitymys ceases to exist in Eurasia, and some species of North America (the "quasiater species group") no 

longer belong in Pitymys. The usage of Chaline and others 

( 1988) is here followed. 

The endemic North American Pitymys and Pedomys 

usually have both Secondary Wings developed, although 

individual variation is great, reflecting the recency of their 

evolution out of Allophaiomys. The development of these 

Wings is not strong, however, and Dimension A-A' is usually large (fig. 13A-F). Dimension B-B', separating the confluent Primary Wings from the Cap and its weakly 

developed Secondary Wings, often is quite large but is 

extremely variable and may be quite narrow; the average 

condition probably is more reduced than in Allophaiomys 

pliocaenicus, but the variability is so great that it is not easily 

noticed. The presence of weak Secondary Wings remains the 

most reliable character to separate Pitymys and Pedomys 

from Allophaiomys. 

The earliest Pitymyini of Eurasia often do not have both 

Secondary Wings. Many early Terricola have only a lingual 

Secondary Wing. By the time that Terri cola had dispersed to 

North America, about 850,000 years ago, the development 

of both Secondary Wings (shortening of Dimension A-A') 

had polarized as a generic character, at least in the dispersing 

lineage, as in the living Eurasia lineages. 

Thus all North American Pitymyini, endemic or immigrant, have both lingual and buccal Secondary Wings. However, in North America the Secondary Wings in Terricola 

are much better developed than they are in endemic North 

American genera (fig. 13G-K; J and K are European). Terricola also differs from the North American Pitymys and 

Pedomys in its prominent shortening of Dimension B-B', 

which easily distinguishes the genus from Allophaiomys. 

In North America, the shortening of Dimension B-B', 

as well as the shortening of Dimension A-A', serves to separate the immigrant "quasiater species group" (Terricola) of 

the tribe Pitymyini from the native "pinetorum species 

group" (Pitymys and Pedomys), in which Dimension B-B' 

may not be shortened or may be only moderately shortened 

on an individual basis and Dimension A-A' is never shortened (Repenning, 1983). 

In the Old World, early morphotypes, having only a 

lingual Secondary Wing but a greatly reduced Dimension 

B-B', have been given names such as "Pitymys hintoni," 

"Pitymys arvaloides," and "Pitymys gregaloides" (based 

upon the configuration of the Cap). These are abundant in 

the early Pleistocene faunas of Eurasia. Some early Eurasian 

individuals with an extremely weak development of the lingual Secondary Wing are similar to advanced Allophaiomys 

(figs. 6D or 9B), except that Dimension B-B' is much more 

constricted, and, of course, all of these early populations of 

Terricola include Allophaiomys morphotypes in their population variation. The retention of Allophaiomys morphotypes in early populations of Terricola persists much longer 

in evolving lineages than it seems to persist in early populations of Lasiopodomys. 

An example of these primitive forms of Terricola 

comes from the Razdolie fauna, south of Bamaul in Western 

Siberia (Zazhigin, 1980, fig. 38; this report, locality 29 in fig. 

1). Based upon figured specimens, this fauna contains intergrading morphotypes of moderately advanced Allophaiomys 

(72 percent) and Terricola hintoni (28 percent). Although 

the present author briefly examined this fauna in Moscow, 

the entire sample has not been counted to eliminate a few 

Lasiopodomys morphotypes (six were illustrated, one as 

Microtus) that were included in the count of, but that do not 

appear to intergrade with, Allophaiomys. A few last upper 

molars are complex (all included in Terricola), and the brief 

examination of the sample in Moscow showed that about 33 

percent of the individuals have "Microtus" enamel-thickness 

differentiation. From the morphotype counts presented, a 

bimodal pattern does not appear evident, and it is not certain 

whether Terricola hintoni should be recognized in the fauna 

or whether a population of Allophaiomys is present with a 

strong Terricola variation. 

The Razdolie fauna also contains Cromeromys intermedius, Mimomys pusillus, "Villanyia," Eolagurus, Prolagurus, and Clethrionomys. From its composition, the fauna 
GENUS PITYMYS 67 

would seem to date from well before the Jaramillo event of 

the Matuyama Chron, but no paleomagnetic control is available. The Razdolie Terricola is much less advanced than that 

which dispersed to North America 850,000 years ago, after 

the Jaramillo event and before the Brunhes Chron. 

Although Terricola in Eurasia and Pitymys and 

Pedomys in North America have separate origins out of Allophaiomys, they are retained in the single tribe Pitymyini. 

Because of the preliminary nature of the phylogeny of these 

descendants of Allophaiomys, suprageneric (tribal) groups 

are not treated as monophyletic in the present report. Basically the function of suprageneric categories is to subdivide 

bewildering arrays of taxa into comprehensible units. Thus, 

the separate origins of Pitymys and Terricola out of Allophaiomys (an unknown number of lineages in Eurasia and 

two in the United States) and the need for different dental 

diagnoses to distinguish them, are not here considered sufficient reason for the establishment of separate tribes. Nor are 

the two, and possibly more, origins of Microtus out of 

Lasiopodomys or the possible multiple origins of Lasiopodomys out of Allophaiomys. As the history of Terricola and 

Microtus is further revealed, tribal subdivision may become 

desirable for clarity in discussion. 

GENUS Pl1YMYS M'MURTRIE, 1831 

(fig. 13A-E; Georgia, U.S.A.; locality 28, fig. 1, exact locality uncertain) 

Type species.-Psammomys pinetorum LeConte, 1830. 

Revised dental diagnosis.-A genus of the tribe Pitymyini with weak Secondary Wings and a large Dimension 

A-A'; often with a large Dimension B-B'; and a simple M\3. 

Triangle 4 (buccal Primary Wing) of first lower molars 

projects posterobuccally-not normal to the tooth longitudinal occlusal midline (fig. 13). Enamel-thickness differentiation is of "Microtus" or intermediate type. 

'iYPICAL" PllYMYS 

Revised dental diagnosis.-As for the genus. 

Comments.-Pitymys pinetorum has been recognized 

as belonging to a strictly North American lineage at least 

since van der Meulen (1978) and suspected as such prior to 

Ognev (1948). Both Secondary Wings on the Cap of the 

Anteroconid Complex are present, but they are poorly developed and Dimension A-A' is large. M\3 is always simple. 

Enamel-thickness differentiation is of either the "Microtus" 

or the intermediate type; the enamel tends to be quite thick. 

The genus is characterized by a moderate to wide 

Dimension B-B' so that, like Allophaiomys, it usually has 

moderate to great dentinal confluence between the Primary 

Wings and the Cap of the Anteroconid Complex; however, 

this confluence has exceptions. Although only 6 of 44 first 

lower molars of Pitymys pinetorum from New Paris #3, 

Pennsylvania (Holocene), were judged to have Dimension 

B-B' completely open, in the remainder the dimension was 

less than half closed. In none was the dimension closed, 

breaking the confluence between the Cap and the Primary 

Wings. On the other hand Paulson (1961) stated that he 

examined 91 specimens of P. pinetorum and counted 40 percent as being closed between the Primary Wings and the 

Cap. More examination of P. pinetorum would seem to be 

needed. Also, a more critical evaluation of uniformity in the 

use of the terms "open," "half closed," and "closed" would 

probably help reduce uncertainties. A question exists regarding the possibility of extreme differences between local 

populations. 

In the population found in the Cheetah Room fauna of 

West Virginia, the genus can be seen to have evolved out of 

Allophaiomys. Judging from the sample seen from the 

Hanover Quarry Fissure fauna, from van der Meulen's 

description of the Cumberland Cave population, and from 

Pfaffs discussion of both Trout Cave No. 2 and Cumberland 

Cave populations, Pitymys cumberlandensis appears to be an 

evolutionary stage of the genus more fixed in its individual 

variability but differing from the living form by lacking 

"Microtus" enamel differentiation in a significant percentage of individuals. 

Van der Meulen (1978) suggested that Dimension 

A-A' of P. cumberlandensis is relatively wider than in 

P. pinetorum so that the reentrants created by its shortening are weaker and not filled with cement; that is, its 

Secondary Wings are less developed (fig. 13). This difference did not seem obvious in the sample of P. cumberlandensis from the slightly older Hanover Quarry Fissure 

here examined. Pitymys cumberlandensis from Cumberland Cave was not examined for the present evaluation, 

as its nature did not seem to be in doubt from published 

accounts; see van der Meulen (1978) for illustrations. 

There appears to be little difference in the morphology 

of Pitymys cumberlandensis from the Hanover Quarry 

Fissure, from Cumberland Cave (van der Meulen, 1978), and 

from Trout Cave No. 2 (Pfaff, 1990). Viewed with the 

awareness of the distinct changes in morphotype modes in 

the Allophaiomys-to-Pedomys and in the Lasiopodomys-toMicrotus populations of these same faunas, this persistent 

lack of individual variability seems unusual. It strongly 

suggests that Pitymys cumberlandensis had achieved morphologic stability (polarization). 

On the other hand, the difference between Pitymys cumberlandensis and the single living species of this genus, 

Pitymys pinetorum, is so slight (a change toward increased 

"Microtus" enamel-thickness differentiation) that it is difficult to believe that the living species does not derive from P. 

cumberlandensis. No other obvious source is known for the 

living species, and Allophaiomys, the ancestral root stock, 

appears to have become extinct, through linear evolution of 
68 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Allophaiomys guildayi into Pedomys, during the existence of 

Pitymys cumberlandensis. 

After the time of the Trout Cave No. 2 fauna, the stability of the character polarization of enamel-thickness differentiation in Pitymys cumberlandensis must have decreased, 

but no fossil record of such has been demonstrated. Although 

an adequate number of populations have not been examined, 

many have reported the opinion that extreme variation characterizes living Pitymys pinetorum. It is suggested that this 

change in character stability may be happening today. This 

is a situation in which the identification of the decrease in 

polarization of enamel-thickness differentiation will require 

the determination of percentages of differentiation in large 

samples of the living species from many local populations. 

Half a dozen or fewer fossil species have been named (see 

Repenning, 1983) and they cannot be properly evaluated 

until the variability of the living species is better known. 

Pitymys lives primarily near trees and has always had a 

distribution confined to open forests and the forest-prairie 

mosaic of the eastern United States. The possibility exists 

that it was competitive with immigrant Terricola, explaining 

their former mutually exclusive distributions. 

GENUS PEDOMYS BAIRD, 1857 

(fig. 13F; Fort Pierre, South Dakota; locality 29, fig. 1) 

Type species.-Pedomys ochrogaster Baird, 1857. 

Revised dental diagnosis.-A member of the tribe 

Pitymyini very similar to Pitymys but with Triangle 4 (buccal Primary Wing) projecting at right angles from the longitudinal occlusal midline of the frrst lower molar (fig. 13F). 

Comments.-The type species has been considered by 

many as belonging in Pitymys. Pedomys, like Pitymys and 

Allophaiomys, has a moderate to wide Dimension B-B' so 

that it has wide dentinal confluence between the Primary 

Wings and the Cap of the Anteroconid Complex. Both 

Secondary Wings on the Cap of the Anteroconid Complex 

are present, and, as in Pitymys, they are commonly poorly 

developed. Dimension A-A' is large; the dimension does not 

seem to average quite as large, however, as in Pitymys. The 

M\3 is always simple. "Microtus" enamel-thickness differentiation is the rule, although in some individuals it is only 

weakly developed. 

From dental characters, distinguishing individuals of 

Pedomys from those of Pitymys is difficult, as many who 

work with the teeth of these genera have stated. Martin 

(1974; enlarged in Martin, 1991) indicated that the first 

lower molars of Pedomys can be distinguished from those of 

Pitymys by the lateral projection of Triangle 4 (buccal Primary Wing), which projects nearly at right angles to the 

occlusal axis in Pedomys, rather than posterolaterally as in 

Pitymys (fig. 13). Pfaff (1990) agreed with this character but 

expressed it in terms of the angle formed by the anterior 

borders of the two Primary Wings (Pedomys >140°; Pitymys 

<135°); he also indicated that the reentrants of Pitymys are 

narrower and curved more to the anterior at their apices than 

are those of Pedomys. 

Paulson (1961) examined 146 specimens of living 

Pedomys ochrogaster and counted 95 percent as being confluent between the Primary Wings and the Cap, differing in 

this great percentage from his observations of Pitymys, 

wherein only 60 percent were confluent There is, however, 

reason to question this observation, as noted previously (p. 

67). These characters may be useful in the identification of 

Pedomys ochrogaster populations for which a large sample 

is available, but are not without exception and are not positive in the identification of individual specimens. 

Pedomys appears to have begun evolving from Allophaiomys guildayi in the Cumberland Cave fauna; it appears 

as a morphotype variant of Allophaiomys (1 percent) in the 

Hanover Quarry Fissure fauna. Van der Meulen (1978) 

stated that about 20 percent of the population from Cumberland Cave has the typical Allophaiomys morphotype, with no 

suggestion of the development of Secondary Wings. The 

remainder of the population has one or two rudimentary Secondary Wings according to his description. What van der 

Meulen's morphologic criteria were is not clear, but the 

present author's count of a part of the same sample indicates 

a different percentage, a condition that is bound to occur 

with different observers because of varying criteria for subdividing a morphologic continuum. Thirty-seven first lower 

molars were available for the present study, but van der 

Meulen stated that he had 200. How the sample available for 

the present study was separated from van der Meulen's is not 

known. 

As previously discussed under Allophaiomys from 

Cumberland Cave (p. 42), 51 percent of the available sample 

of Allophaiomys guildayi has a "typical" Allophaiomys morphology, 32 percent has an "advanced" Allophaiomys morphology with a posterolingual angularity on the Cap, and 16 

percent has a Pedomys morphology with both Secondary 

Figure 13 (facing page). Pitymys and Terricola, first lower and 

last upper molars. A, Pitymys hibbardi, Cheetah Room fauna, West 

Virginia, individual overlapping Allophaiomys morphotype; 

USNM specimen. B, Pitymys hibbardi, Cheetah Room fauna, West 

Virginia, typical individual; USNM specimen. C, Pitymys hibbardi, 

Cheetah Room fauna, West Virginia, individual overlapping Pitymys cumberlandensis morphotype; USNM specimen. D, Pitymys 

cumberlandensis, Hanover Quarry Fissure fauna, Pennsylvania; 

CM specimen. All the following (E-K) have "Microtus" enamelthickness differentiation: E, Pitymys pinetorum, New Paris fauna, 

Pennsylvania (fossil). F, Pedomys ochrogaster, Kansas (living). G, 

Terricola meadensis, Locality CT -2, oldest faunas in Hansen Bluff 

faunal sequence, Colorado (fossil). H, Terricola meadensis, Cudahy fauna, Kansas (fossil)./, Terricola quasiater, Vera Cruz, Mexico, UCMVZ specimen (living). All the preceding have simple 

M\3s. J, Terricola subterraneus, Belgium, M/1 and associated 

complex M\3 (living). K, Terricola duodecimcostatus, Spain, M/1 

and associated simple M\3 (living). The last is a "rhomboid" M\3. 
GENUS PEDOMYS 69 

F G H I 

J K 

0 1 2mm 
70 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Wings in clear evidence, although never well developed. 

Such counts, of course, vary with the counter, and one may 

consider an enamel irregularity insignificant while another 

will consider lt as certain evidence. 

It seems probable that what is here considered as 

"advanced Allophaiomys" was considered as Pedomys by 

van der Meulen, and such a judgment could be defended by 

pointing to the variability observed in living Pedomys. But 

van der Meulen's method of judging would seem to eliminate 

half the type population from Betfia-2, and this is not justified. However, there remains the uncertainty of how the 

sample seen in the present study was separated from that 

examined by van der Meulen; the selection might have been 

biased. 

To the extent that the present author has seen the type 

population from Cumberland Cave, Allophaiomys guildayi 

has a morphologic variation with 16 percent overlap of the 

Pedomys morphotype. Pfaff (1990) had access to the Cumberland Cave fauna and also referred the species to Allophaiomys. Earlier, Repenning (1983) made the same judgment 

from consideration only of van der Meulen's illustrations 

(1978, fig. 7), which contain only one Pedomys morphotype 

and eight specimens of "typical" and "advanced" Allophaiomys morphotypes. 

Allophaiomys guildayi from Hanover Quarry Fissure 

fauna has the Pedomys morphotype in 7 percent of the sample; the minimum of 16 percent in the Cumberland Cave 

fauna (by the same counter) suggests advancement toward 

Pedomys and a somewhat younger age. The sample of 

Lasiopodomys from Hanover Quarry Fissure, though of 

inadequate size, suggests the same advancement. The possible age relationships are discussed under Allophaiomys from 

Cumberland Cave (p. 42). 

PEDOMYS ILANENSIS HIBBARD, 1944 

Discussion.-In 1944, Hibbard introduced the name 

Pedomys llanensis for a form from the Cudahy fauna of Kansas (610,000 years old). His illustration of the type specimen 

indicates a very weakly developed buccal Secondary Wing, 

and none is shown on the lingual side. As the lingual one is 

usually the first to form in this lineage and as it is suggested 

by an angular posterolingual comer on the Cap as illustrated, 

it seems probable that the lingual Secondary Wing had been 

present but was obliterated by wear of the tooth. Hibbard 

apparently had only one specimen, the type, although he 

mentioned a right and a left lower jaw. In 1961, Paulson 

illustrated a second left ramus from Cudahy and mentioned 

at least four individuals. He also noted the presence of slight 

fifth lingual and fourth buccal reentrants; these reentrants are 

those anterior to the Secondary Wings and their presence is 

necessary for the angular comers of the Cap to be called 

Wings. 

Van der Meulen (1978) separated Pedomys guildayi 

from Pedomys llanensis on the basis of a wider Cap (relative 

to the width of the Primary Wings) and a longer Anteroconid 

Complex (relative to the total length of the tooth) in P. llanensis. These are features that result from the increase in the 

complexity of the Cap (or, in his ratios, result in a narrowing 

of the width across the Primary Wings), and thus their 

increase is a derived character relative to the condition in 

ancestral Allophaiomys. He also stated that the confluence 

between the Cap and the Primary Wings (Dimension B-B') 

is less in Pedomys llanensis; this appears to be true of the 

specimen figured by Paulson (1961) but not of the type figured by Hibbard (1944). 

Van der Meulen did not have an opportunity to study 

the type or other topotypic material from the Cudahy fauna; 

they also were not available for the present study. Published 

accounts seem to indicate that possibly only five individuals 

are known from the type locality-too few to know what the 

typical morphology might be. 

The oldest unquestioned population of Pedomys llanensis is that from Trout Cave No.2, West Virginia, which was 

described by Pfaff (1990). The sample of this population of 

the species includes morphotypes of Allophaiomys pliocaenicus (<10 percent), A. guildayi, and Pedomys llanensis (66 

percent), and Pfaff noted that more than 90 percent have the 

development of at least one Secondary Wing (Pfaff, 1990, 

fig. 5A) and that 66 percent show the development of both 

(Pfaff, 1990, fig. 5). Less than 10 percent are described as 

having an Allophaiomys pliocaenicus morphotype (Pfaff, 

1990, fig. 5E), and the sample apparently shows a Pedomysmode with individual variation overlapping primarily the 

advanced Allophaiomys species morphotype. 

This composition of the Pedomys population from 

Trout Cave No.2 and the lack of Lasiopodomys variants in 

its sample of Microtus paroperarius indicate an age younger 

than Cumberland Cave, as concluded by Pfaff. The stage of 

advancement of the Microtus first lower molars (his fig. 4) is 

comparable to that known from the oldest faunas of Hansen 

Bluff, Colorado, but includes a few individuals with a more 

prominently reduced Dimension A-A', and only complex 

last upper molars were assigned. The Trout Cave No. 2 fauna 

is thus considered to be somewhat younger than the oldest 

faunas of Hansen Bluff (820,000 years), but probably not as 

young as the youngest faunas of this Colorado faunal 

sequence (approximately 700,000 years). Pfaff noted that the 

fauna appears clearly older than the Cudahy fauna of Kansas 

(610,000 years), and it is here assigned an approximate age 

of 725,000 years. 

The Trout Cave No. 2 fauna also contains Pitymys cumberlandensis in a population that seems no different than that 

of Cumberland Cave or Hanover Quarry Fissure, again 

suggesting a polarity of individual variation in this extinct 

species, as has been discussed. 

The species Pedomys llanensis had been recognized in 

several other faunas (Wathena, Kentuck, and Sappa), until 

Martin (1975) pointed out that the fossils so identified were 
GENUS TERRICOLA 71 

very similar to Allophaiomys pliocaenicus. Thus these other 

records do not help in the recognition of P. llanensis. 

Pfaff (1990) noted the similarity of Pedomys llanensis 

to living P. ochrogaster and suggested that they might be 

conspecific, the principal difference being that older populations have, apparently, greater individual variability. But he 

also noted that considerable variability still exists in the living species. Graham (1972) reported the existence of about 

30 additional first lower molars of P. llanensis from the 

Cudahy fauna and an equal number from Conard Fissure, 

Arkansas. The present author has not seen these and has not 

been able to confirm the existence of 30 additional first 

lower molars from Cudahy. 

Living Pedomys is more of an open grassland animal 

than is Pitymys and has a distribution farther west, extending 

across the Great Plains westward to the foot of the Rocky 

Mountains. It does not live in the mountains and, as noted, it 

is not present in northeastern North America; its range 

appears to be exclusive of areas cooled in the summer by arctic air or higher topography. However, its modem range does 

not extend as far south as did that of Allophaiomys, and in 

contrast to Allophaiomys, it coexists with Microtus in the 

southern part of the range of the latter. 

GENUS TERRICOLA FATIO, 1867 

(figs. lOB, 13G-K; Lake Geneva, Switzerland; locality 35, fig. 1) 

Type species.-Fatio did not designate a type species 

for Terricola but erected it as a subgenus to include both 

Terricola savii and Terricola subterraneus. The ranges of 

the two rather different species (this report, fig. 13J, K) overlap in the type area. Terricola savii, as grouped by Corbet 

(1978), is a southern European form that has a simple last 

upper molar in many populations (includes T. duodecimcostatus, this report, fig. 13[(). Terricola subterraneus is a 

northern species with a complex M\3 (this report, fig. 13J). 

Many other living species have been named. 

Revised dental diagnosis.-A genus of the tribe Pitymyini with strong Secondary Wings, wide to very narrow 

Dimension A-A', very narrow to closed Dimension B-B', 

and "Microtus" enamel-thickness differentiation. Last upper 

molar complex or simple. 

"TYPICAL" TERRICOLA 

Revised dental diagnosis.-As for the genus. 

Comments.-On the basis of the last upper molar alone, 

the genus Terricola appears in need of subgeneric subdivision. Kratochvil (1970) has examined many characters 

in an effort to subdivide and classify Terricola; Kratochvil 

and Kral (197 4) have identified two major groups on the 

basis of karyotypes. Brunet-Lecomte and Chaline (1990) 

have examined European fossil and living species and have 

suggested a rather complicated, but nonetheless plausible 

evolutionary history. However, their analysis does not 

consider Asiatic and North American populations, nor the 

morphology of the last upper molar, which, in contrast with 

its significance in the tribe Microtini, appears so variable that 

it seems useless. No characters used in these attempts to subdivide Terri cola of Europe and western Asia seem to match 

well with characters in the others; each attempt at subdivision seems to produce different geographic groupings, and in 

many populations individual variation appears to be great. 

Discussion.-Unlike Pitymys and Pedomys, the genus 

Terricola has a very narrow to closed Dimension B-B' 

resulting in little or no confluence between the Cap and the 

Primary Wings. Dimension A-A' is also narrow in most living forms, and in most individuals Secondary Wings are 

strongly developed (fig. 130-K). This character is much less 

prevalent in fossil species. In North America, Terricola has 

only "simple" last upper molars except for a few individuals 

of the living Terricola quasiater (east-central Mexico), 

which seem today to be developing a more derived last upper 

molar. This condition contrasts with many, but not all, Eurasian species (Repenning, 1983 ). Possibly a situation similar 

to that of the Mexican population may explain the variability 

reported in the Eurasian species, and it may be decipherable 

only on a "percentage of the population" basis. The Eurasian 

living Terricola populations have a variability in the complexity of the last upper molar comparable to that seen in 

Microtus paroperarius in the oldest faunas (820,000 years) 

of the Hansen Bluff faunal sequence; in some living Terricola lineages polarization to a complex last upper molar may 

only be in progress. 

In Eurasia, species that have a simple M\3 are southerly 

in distribution (Miller, 1912), suggesting a distribution of 

more primitive relics. But the geographic pattern is not simple. Kratochvil (1970) recorded individual variation between 

simple and complex last upper molars in some species (such 

as Terricola tatricus) and tentatively identified five to seven 

geographic species groups; Miller (1912) also recognized 

many species groups by grouping them on the basis of last 

upper molar complexity. 

With the possible exception of Pitymys pinetorum nemoralis, whose specific affinity (and now generic, with the 

separation of Pitymys from Terricola) Repenning (1983) 

questioned, North American Terricola appears to be now 

confined to central Mexico, although once widespread in the 

central and western United States. 

The tooth shown in figure lOB is that of Terricola 

meadensis (Hibbard) from an undated locality in the AnzaBorrego Desert of California (LACM Loc. 68123). It is 

from a locality within the depositional sequence that was 

studied magnetically (J.A. White, written common., 1990) 

and below the youngest normal polarity zone. Other 

records of Terricola in the United States, all west of the 

Mississippi River but both east and west of the Rocky 

Mountains (Repenning, 1983), indicate that this species is 

not known before the dispersal event 850,000 years ago. 
72 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

These post-Jaramillo-event localities include Californian 

localities as far north as the San Francisco area and Cape 

Mendocino (localities 22 and 23, fig. 1). Thus the youngest 

normal polarity of the Anza-Borrego Desert study is not 

the Jaramillo event, as was supposed by Johnson and others 

(1984 ), but the Brunhes Chron. The oldest closely dated 

records of Terricola meadensis are in the 820,000-year-old 

faunas of the Hansen Bluff faunal sequence. The type is 

from the Cudahy fauna of Kansas, 610,000 years old. 

It is believed that Terricola meadensis entered the 

United States, with Lasiopodomys, by way of the dispersal 

route on the east side of the Rocky Mountains and spread 

over the Great Plains between 850,000 and 610,000 years 

ago. At the time of its entry into the area of the United States, 

Terricola seems to have continued south past Hansen Bluff, 

Colorado, westward around the south end of the Rocky 

Mountains to southern California, and then northward up the 

Pacific Coast to nearly the northern limit of California. The 

genus is known from high in the Rocky Mountains (Hansen 

Bluff, 7,546 ft elevation, and Porcupine Cave, 9,500 ft elevation) and from sea level at the head of the Gulf of California (Anza-Borrego Desert) and at Cape Mendocino, northern 

California (Repenning, 1983; localities 15, 21, 22, and 23, 

fig. 1). This is a remarkable range in environment from what 

must have been subalpine meadows in Colorado to the northem fringes of subtropical coasts at the head of the Gulf of 

California. The obstacle preventing Lasiopodomys from also 

following this route was probably the presence of warmer 

climate around the south end of the Rocky Mountains, as 

other parts of the history of this genus indicate arctic to temperate climate preferences. 

The immigrant Terricola meadensis was present only in 

the western areas of the United States (Cudahy, Hansen 

Bluff, Porcupine Cave, and other localities both east and 

west of the Rocky Mountains), and its absence in the Appalachian faunas (Cheetah Room, Hanover Quarry Fissure, 

Cumberland Cave, and Trout Cave No. 2 faunas) is a feature 

of the eastern United States; it has never been reported from 

east of the Mississippi River (Repenning, 1983). 

Although an immigrant, with Lasiopodomys, from 

Beringia to the United States 850,000 years ago, Terricola is 

unknown in the Beringian fossil record. It Is unknown from 

the several localities of the Old Crow basin in northern 

Yukon Territory, unknown in Alaskan fossil and living 

faunas, and unknown in northeastern Siberia, either fossil or 

living. Yet it certainly passed through Beringia and appears 

to have done so between 875,000 and 820,000 years ago. 

Terricola meadensis does not appear to have stayed in 

Beringia very long, and unquestionably the coldest environments in which it has been found are those along the east 

edge of the Rocky Mountains of Colorado, at the Hansen 

Bluff locality (Rogers and others, 1985; 7,546 ft (2,300 m) 

elevation; during the Nebraskan glaciations) and Porcupine 

Cave locality (Bamosky and Rasmussen, 1988; 9,500 ft 

(2,900 m) elevation; possibly during the Kansan glaciation). 

At about the same time that it lived at Hansen Bluff, it also 

lived in hot subtropical wet climates near sea level at the 

head of the Gulf of California in the region of the modem 

Anza-Borrego Desert of California. Its known past range is 

broad in the region now occupied by the Temperate Zone but 

was mainly in warm-temperate to subtropical regions. The 

fossil record of Terricola does not speak for very intensive 

cold during the earlier glaciations of the United States 

(Repenning, 1983). 

No southward dispersal from Beringia took place down 

the west side of the Rocky Mountains 850,000 years ago; a 

combination of rising coastal mountains in western Canada 

and southern Alaska and increased mountain glaciation, 

which flowed into the Pacific Ocean, appears to have obliterated a coastal plain environment suitable for dispersal as 

well as erecting walls of ice across the route (Repenning, 

1990). 

The lack of a record of Terricola in Beringia suggests 

that the genus did not linger there when dispersing to North 

America but moved southward ahead of the first Nebraskan 

ice sheet; nor does it live in arctic environments today. Terricola seems to have decided temperate preferences. The 

fact that it did disperse to North America thus suggests a 

period, probably brief, of temperate climate in Beringia just 

before the first Nebraskan ice advance. Scant evidence exists 

for such a Beringian warm period at this time, except that little record seems to exist of deposition during the 50,000 

years between the Jaramillo event and the first Nebraskan ice 

sheet. Such a hiatus is known at least in Yakutia and Yukon 

Territory, as will be discussed in the section, "Age of 

Krestovka Olyor and Cape Deceit faunas" of this report. 

Other than avoiding arctic climates, Terricola seems to 

have had great adaptability, from subtropical sea levels 

along the Mexican border in southern California to 9,500-ft 

subalpine valleys in the eastern parts of the Rocky Mountains. This adaptability seems to suggest that competition, 

rather than environmental constraints, caused the failure of 

the genus to occupy the United States east of the Mississippi 

River. It now exists as a relict population in the eastern 

slopes of the Sierra Madre Oriental in central Mexico. 

SYSTEMATIC SUMMARY 

(fig. 14) 

Allophaiomys is a member of the tribe Arvicolini 

because it has a first lower molar with fully confluent Primary Wings and a Cap uncomplicated by Secondary Wings. 
SYSTEMATIC SUMMARY 73 

Dimension A-A' equals the width of the Cap (that is, the 

dimension does not exist); Dimension B-B' is wide and little 

reduced; Dimension C-C' is wide and little reduced; M\3 is 

simple; enamel differentiation is primarily "intermediate"; 

and hypsodonty is advanced so that roots do not form on the 

cheek teeth. 

The tribe Microtini.-The tribe Microtini formed out of 

Allophaiomys by complications of the Anteroconid Complex. The frrst complication is the separation of the two Primary Wings by the reduction of Dimension C-C', forming 

Triangle 4. Further complications consist of (1) reduction of 

Dimension B-B' to greatly narrow or eliminate the dentinal 

contact between the lingual Primary Wing and the Cap, ultimately forming Triangle 5; (2) establishment and reduction 

of Dimension A-A' to develop Secondary Wings (Triangles 

6 and 7); (3) complication of the posterior loop of the last 

upper molar; and (4) the development of "Microtus" 

enamel-thickness differentiation. These numbered further 

complications develop at rates that are independent of each 

other and define the genera of the tribe. 

Lasiopodomys shows only separation of the Primary 

Wings and no further complications, although "Microtus" 

enamel-thickness differentiation may develop variably. Living species, in the Oriental faunal region of Asia, appear to 

be at about the same stage of evolution as were the frrst 

Microtus that evolved out of Lasiopodomys; they are 

believed to have developed in the Oriental region by evolution parallel to the other Lasiopodomys lineage present 

throughout the Northern Hemisphere. Multiple origins of 

non-Chinese Lasiopodomys (out of Allophaiomys) also seem 

possible. 

Microtus shows further complication (2), establishment 

and reduction of Dimension A-A' with the development of 

Secondary Wings; it may also show further complications 

(1), reduction of Dimension B-B', and (3), complication of 

the posterior loop of M\3. Except for the earliest forms, 

further complication (4), "Microtus" enamel-thickness differentiation, is almost universal. Multiple origins out of 

different populations of Lasiopodomys on different continents at different times seem obvious. 

The subgeneric and specific subdivisions of Microtus 

result from the variations in rates of these further complications and are not yet clearly documented. Better documentation of the fossil record of Lasiopodomys will assist 

understanding of the lineages of Microtus, for different 

lineages presumably evolved out of different populations of 

Lasiopodomys in different regions. 

Proedromys is unique in that it shows a reduction, 

rather than complication, of the posterior loop of the last 

upper molar, but otherwise resembles Lasiopodomys. Its 

fossil and living records suggest no diversification or major 

dispersal, and it may have developed only in the Oriental 

region by evolution parallel to Lasiopodomys. 

The present fossil record suggests that the North American genus Lemmiscus evolved directly out of Allophaiomys 

perhaps 870,000 years ago in the southeastern Rocky Mountains of New Mexico and that this lineage experienced no 

diversification after this time. Its unique characters are the 

presence of a last upper molar with an elongate posterior process but only two alternating triangles anterior to it, of only 

a buccal Secondary Wing on the first lower molar, and of 

cement in the tooth reentrants. Like Proedromys in China, 

Lemmiscus in western United States seems to have experienced no major (global scale) dispersal from its area of 

origin (Rocky Mountains), nor diversification. 

Rather than being typical of either the eastern or the 

western regions of the United States, Lemmiscus appears 

unusual in that it appears to have originated within the Rocky 

Mountains and spread both east and west into both provinces. Its two oldest records are in Colorado within the eastem part of the Rocky Mountains. 

The tribe Pitymyini.-The tribe Pitymyini developed 

out of Allophaiomys by complications of the Anteroconid 

Complex, the frrst of which is establishment and reduction of 

Dimension A-A' to develop Secondary Wings (Triangles 6 

and 7). Further complications consist of (1) reduction of 

Dimension B-B' to narrow or eliminate the dentinal confluence between the Primary Wings and the Cap, (2) shortening 

of Dimension A-A' to make the Secondary Wings more 

prominent, (3) complication of the posterior loop of the last 

upper molar, and (4) development of "Microtus" enamelthickness differentiation. These numbered further complications develop at rates that are independent of each other, and 

their variations define the genera of the tribe. No subgenera 

are recognized, although they might be as justifiable as they 

are in Microtus. 

Pitymys is variable in the presence of further complication (1), reduction of Dimension B-B', and usually does not 

show it; the genus does not experience further complication 

(2), to produce prominent Secondary Wings, or further complication (3), to produce a complex last upper molar. Further 

complication (4), development of "Microtus" enamel differentiation, is variable and, because thick enamel is prominent 

in the genus, the differentiation is not always conspicuous; 

the genus may now be in the process of developing further 

complication ( 4) in the living fauna. 

Pitymys evolved in North America out of Allophaiomys 

and appears always to have had an eastern distribution 

within the eastern region of the United States. 

Pedomys usually does not experience further complication (1), reduction of Dimension B-B', but otherwise has the 

same variability of further complications as does Pitymys. 

Triangle 4 usually projects normally from the tooth axis 

rather than posterolaterally as in Pitymys. Pedomys also 

evolved in North America out of Allophaiomys, but at a 

slightly later time than did Pitymys. 
74 AUOPHAIOMYS AND THE OL YOR SUITE, Y AKUTIA 

POLARITY 

TRIBE PITYMYINI 

EXPLANATION 

OJ ROOTLESS 

[]] A-A' AND EHl' REOU::ED 

i1J C-C' REDUCED 

I1J LAST uPPER MOLAR REDUCED 

[I) A-A' REDUCED, LAST UFI'ER MOLAR COMPLEX 

[§) A-A' WEAK 

I2J LAST UFI'ER MOLAR c:avPLEX 

(§] BUCCAL SECONDARY WING, 

M13 WITH ELONGATE POSTERIOR LOOP 

l2] UNCERTAIN 

• EXTERNAIL AGE CONTROL 

TRIBE MICROTINI 

IRVINGTON 

Figure 14. Phylogenetic diagram of genera of the Microtini and the Pitymyini herein discussed. Based upon present information. 

Geography is not indicated. Time and geopolarity are. Broken connecting lines at lower right, origin uncertain: possibly from Oriental 

faunal region. 

Pitymys and Pedomys are not diverse and did not disperse to the Old World or west of the Rocky Mountains in 

North America. 

Terricola experienced all listed further complications 

and evolved in the Old World. It dispersed to North America 

about 850,000 years ago at a stage when the dispersing 

lineage had not yet experienced further complication (3), 

complex M\3; the population ofTerricola that immigrated to 

North America had already experienced further complications (1), shortening and closure of Dimension B-B', 

and (2), shortening of Dimension A-A'. The North American population of Terricola may now be experiencing further complication (3), complex M\3. Like Pitymys, North 

American Terricola is not consistent and may or may not 

have "Microtus" enamel-thickness differentiation (further 

complication (4)). 

The Eurasian species of Terricola appear to be divisible 

on the basis of whether or not further complication (3), complex M\3, has been experienced in their lineage, but the 

present record indicates current lack of polarity in many 

species. However, complicated last upper molars are a 

progressive character in all lineages of the subfamily Arvicolinae except that leading to Proedromys. 

The genera Herpetomys, Neodon, Orithriomys, and 

Tyrrhenicola are of uncertain affinity, in the author's mind. 

PROVINCIALITY 

Among the descendants ofAllophaiomys, differences in 

age of less than 10,000 years are inferred from progressive 

morphologic change within lineages; they are supported by 

other aspects of the fossil fauna as there are, currently, no 

age-determining methods which discriminate such brief time 

periods. The pattern of such rapid evolution cannot be calibrated with less accurate time control, and the age of stages 

of evolutionary change between times controlled by extrinsic (external) methods must be interpolated. Interpolation 

requires an estimate of proportionate change, and the 

assumption that the rate of change was uniform. A similar 

assumption, that the rates of deposition and evolution were 

uniform, is used to interpolate age in deep sea cores, possibly 

with less justification because it has often been demonstrated 

that the rate of deposition does change. Similarly, it is rather 

clear from the microtine fossil record that environmental 

change stimulates evolutionary change. These influences 
PROVINCIALITY 75 

require that attention to depositional and environmental 

change be maintained. 

Because of the rapid rates of morphologic change in 

microtine rodents, their provincial history must also be a 

consideration in interpreting their evolution. Over short 

periods of time, microtine populations can change greatly 

within a province, and these changes need not resemble 

those that took place in other provinces. Still, these changes 

can be so similar that they cloud recognition of provenance. 

Consequently, the integration of provincial histories around 

the world is impossible without an awareness of their differences and of interprovincial faunal exchanges. What came 

from Asia to Beringia as Lasiopodomys may have left 

Beringia for the United States as Microtus. 

Without knowing the direction and rate of evolution, 

the constraints of climate and geography, the morphologic 

definitions of taxa, and without time control, one has no 

basis for interpreting microtine history; evolutionary paths 

would be assumed rather than demonstrated, and the magnitude of possible error in such an assumption increases with 

the rate of evolution. All factors are critical to understanding, and the neglect of any one leaves questionable any 

interpretation. 

The record ofmicrotine rodent history, at least in North 

America, is now known well enough to indicate that this history can be quite different in different faunal regions. It is as 

obvious in the past as it is today that the microtine fauna in 

the arctic region is not the same as that in Spain. It also is 

obvious that the distribution and composition of microtine 

faunas change with changes in climate. The appearance or 

disappearance of any taxon in Europe does not necessarily 

have the same temporal significance as it does in central 

Asia, or other areas. Faunal regions were no less distinct in 

the past than they are today, and the time and direction of 

evolution are determined by provincial ecosystems; microtine evolution is mosaic. This is illustrated by the polyphyletic origins of Microtus. 

The following detailed demonstration illustrates the 

present lack of certainty regarding at what times and in what 

regions Microtus evolved out of Allophaiomys and the need 

to understand provinciality before inferring the origin of taxa 

and the timing of biochronology. This illustration has been 

mentioned repeatedly throughout this report, but serves as a 

summary of the preceding discussions of fossil faunas and 

their composition. And it is a significant consideration in the 

evaluation of the age of the Olyor Suite of the Krestovka 

Sections in Y akutia. 

1. SAM Cave, New Mexico (first discussed in the 

present publication) contains several fossil faunas representing populations of Allophaiomys that are morphologically 

advanced from the condition found in the typical Allophaiomys pliocaenicus (figs. 3, 6). A few individuals overlap the 

morphology of Lemmiscus (fig. 6F, G). Absent are 

immigrant Terricola and Lasiopodomys, and native Pitymys, 

Pedomys, and Microtus, denoting a later age. Present are 

cool and moist climate indicators (primarily Canadian forests and prairies of today) of the Irvingtonian I microtine 

age,Mictomys l«lnsasensis, ?Phenacomys, and the frrstLemmiscus. This locality is at 8,900 ft (2,728 m) elevation, one 

of the highest fossil microtine faunas in the United States. 

Preliminary paleomagnetic determinations indicate that the 

BOT -4- fauna of SAM Cave lived shortly after the Jaramillo 

event-less than 900,000 years ago. The BOT -4- fauna is in 

reversed deposits above the Jaramillo event and is arbitrarily 

assigned the age of about 875,000 years; it is older than the 

immigration of Lasiopodomys and Terricola 850,000 years 

ago. 

2. The Hansen BlutT faunal sequence, Colorado 

(Rogers and others, 1985) is 39 miles ( 62 km) northeast of 

SAM Cave and is from deposits within the same broad valley 

of the Rio Grande, which, for the most part, has been in its 

present valley for almost 5 million years (Repenning and 

May, 1986). This faunal sequence is at 7,546 ft (2,300 m) 

elevation, also one of the highest fossil microtine faunas in 

the United States. The oldest faunas of the Hansen Bluff 

sequence have no Allophaiomys or Lasiopodomys, but these 

faunas have primitive Microtus (fig. 12A) recently derived 

from immigrant Lasiopodomys. Immigrant Terricola meadensis (fig. 13G) and native Mictomys l«lnsasensis are present 

in the fauna. Native Synaptomys is not present although it 

has a presumably earlier record (earlier because it does contain Allophaiomys morphotypes) from Fyllan Cave, Texas 

(A.J. Winkler, written common., 1990). Lack of Synaptomys 

is believed to reflect the high elevation of Hansen Bluff and 

climatic conditions at the beginning of the glacial ages. 

Paleomagnetic stratigraphy, dated tephra, and climatic 

correlations at Hansen Bluff date its oldest Microtus as 

having been alive shortly before the Brunhes Chron-about 

820,000 years ago (Rogers and others, 1985). More 

advanced Microtus of Beringian-Asian origin is known 

earlier in northern and southern Canada (fig. 7D) and west of 

the Rocky Mountains in the United States (fig. lOA, C). The 

provincial age differences of the earliest Microtus are significant, but, thus far in this summary, the significance is 

unexplained. 

In the Hansen Bluff faunal succession the primitive 

Microtus grades upsection into typical Microtus paroperarius, named from the 610,000-year-old Cudahy fauna of 

Kansas. Computation of sediment rates, based upon paleomagnetic and tephra age controls and climatic cycles in the 

lower part of the section, suggests that the youngest part of 

the Hansen Bluff sequence is about 700,000 years old 

(Rogers and others, 1985). Climatic changes through this 

section are interpreted in this same reference. 

3. The Cheetah Room fauna, West Virginia 

(Repenning and Grady, 1988) contains three microtine populations pertinent to this summary: 

A. Immigrant Lasiopodomys deceitensis with 25 

percent of its individual variation overlapping primitive 
76 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Microtus paroperarius (fig. 111, K). This fauna records a 

morphotype trend in Lasiopodomys toward that of Microtus; 

it is not the only fauna in the world to do so. 

B. Nearly typical Allophaiomys (fig. 8) grading into a 

second morphologic mode that typifies endemic North 

American Pitymys, which, in tum, has individual variation 

that overlaps Pitymys cumberlandensis (fig. 13A-C). This 

fauna records the beginning of the genus Pitymys. 

C. And a morphologic gradation from Mictomys into 

Synaptomys, endemic North American lemmings. The 

intergradation shows the origin of the living genus Synaptomys, and so indicates an age older than other records of 

this genus. In the present report the Mictomys/Synaptomys 

intergradation is of importance only in age considerations. 

No paleomagnetic control is available for the Cheetah Room 

fauna, but North American Synaptomys is known from preBrunhes faunas, as Fyllan Cave, Texas (A.J. Winkler, 

written common., 1990), indicating that the Mictomys-toSynaptomys diversification of the Cheetah Room fauna must 

be older than the Brunhes Chron (beginning 790,000 years 

ago). 

The Cheetah Room fauna postdates the immigration of 

Lasiopodomys and Terricola to North America (about 

850,000 years ago) because it contains Lasiopodomys. It is 

distinctly older than the oldest fauna of Hansen Bluff 

(820,000 years) in having Lasiopodomys and Allophaiomys 

present. It is older than the Hanover Quarry Fissure fauna 

and the Cumberland Cave fauna in lacking a polarized 

Pitymys population, in lacking polarized Synaptomys and 

Mictomys populations, and in having a lower percentage of 

Microtus morphotypes in jts Lasiopodomys population. 

Arbitrarily the Cheetah Room fauna is assigned an age 

of about 840,000 years (10,000 years after the immigration 

of Lasiopodomys; 10,000 years before the transition of 

Lasiopodomys into Microtus in Cumberland Cave; and 

20,000 years before the extinction of Lasiopodomys and 

Allophaiomys, which are not present in the 820,000-year-old 

Hansen Bluff fauna). 

4. The Hanover Quarry Fissure fauna, Pennsylvania (Guilday and others, 1984) contains three pertinent 

microtine populations: 

A. Pitymys cumberlandensis, with no individual gradation into Allophaiomys as was found in the Cheetah Room 

fauna (fig. 13D). This species is also found in the Cumberland Cave fauna and in the Trout Cave No. 2 fauna, and may 

be changing into the living Pitymys pinetorum in the modem 

fauna. 

B. Allophaiomys guildayi with individual variation 

overlapping Pedomys (fig. 9E, F). The same variation was 

found in the Cumberland Cave fauna, but with a significantly 

greater percentage of the Pedomys morphotypes. Still 

greater overlap toward Pedomys is found in the Trout Cave 

No. 2 fauna, where, because of its majority of Pedomys morphotypes, the population is assigned to Pedomys llanensis 

(Pfaff, 1990). The Hanover Quarry Fissure population is 

clearly almost all Allophaiomys morphotypes. Although 

assigned to a species of Pedomys, the Trout Cave No. 2 population retains a few individuals that are of the Allophaiomys 

morphotype. 

C. ?Lasiopodomys of an advanced form (fig. 11L, M) 

similar to some of the morphotypes of this genus in the 

Lasiopodomys-Microtus population of Cumberland Cave, 

and as a variant of Lasiopodomys in the Cheetah Room 

fauna But no Microtus morphotypes were found in Hanover 

Quarry Fissure, suggesting an age older than Cumberland 

Cave (a suggestion weakened by the small sample size). 

Pitymys did not grade into Allophaiomys, suggesting an age 

younger than the Cheetah Room fauna. 

The Hanover Quarry Fissure fauna is younger than the 

Cheetah Room fauna and probably older than the Cumberland Cave fauna by virtue of these comparisons. However, 

these comparisons are only suggestive with respect to the 

Cumberland Cave fauna, and the two faunas are believed to 

be nearly the same age. Arbitrarily the Hanover Quarry 

Fissure fauna is assigned an age of 835,000 years. 

5. The Cumberland Cave fauna, Maryland (van 

der Meulen, 1978) contains four pertinent microtine 

populations: 

A. Immigrant Lasiopodomys deceitensis morphologically overlapping Microtus paroperarius. Both were called 

Microtus by van der Meulen (1978), but the population is 

almost exactly intermediate between the two genera. This is 

advanced over the condition found in the Cheetah Room 

fauna in which only a small percentage of Microtus morphotypes were present in a Lasiopodomys population. 

B. Allophaiomys overlapping the morphology of living North American Pedomys (named Pedomys guildayi by 

van der Meulen, 1978). The population is advanced over the 

condition in Hanover Quarry Fissure fauna in its greater percentage of Pedomys morphotypes, but is considerably less in 

this percentage than Trout Cave No.2. The major part of the 

population has an Allophaiomys morphotype and is assigned 

to this genus. 

C. A primitive form of Pitymys inseparable from Pitymys pinetorum except for enamel-thickness differentiation 

(called Pitymys cumberlandensis). This is the further result 

of the Allophaiomys/Pitymys intergradation seen in the 

Cheetah Room fauna, but is the same as in Hanover Quarry 

Fissure and Trout Cave No 2. 

D. And both Mictomys and Synaptomys but with no 

indication of morphologic overlap as in the Cheetah Room 

fauna (Repenning and Grady, 1988). 

The Cumberland Cave fauna is clearly older than both 

the Cudahy fauna of Kansas (610,000 years) and the oldest 

Hansen Bluff faunas (820,000 years) because of the presence 

of a primitive stage in the Microtus-Lasiopodomys transition. It is younger than the Cheetah Room fauna (about 
PROVINCIALITY 77 

840,000 years) by virtue of the above comparisons, and its 

fauna suggests that it is younger than, but nearly the same 

age as, the Hanover Quarry Fissure fauna. Arbitrarily, the 

Cumberland Cave fauna is assigned an intermediate age of 

830,000 years, 5,000 years younger than the similar Hanover 

Quarry Fissure fauna and 10,000 years older than the obviously more advanced oldest Hansen Bluff fauna. 

6. Trout Cave No.2 fauna, West Virginia (Pfaff, 

1990) contains: 

A. Pedomys llanensis containing a minor percentage 

of variants that overlap Allophaiomys, an advancement over 

Cumberland Cave. 

B. Pitymys cumberlandensis apparently no different 

than that in Cumberland Cave or Hanover Quarry Fissure. 

C. Microtus paroperarius lacking morphologic overlap with Lasiopodomys deceitensis, an advancement over 

Cumberland Cave. 

Advanced morphologies of the frrst lower molar and the 

lack of simple last upper molars of Microtus paroperarius 

from Trout Cave No. 2 indicate an age younger than the oldest faunas of Hansen Bluff (820,000 years) but probably 

older than the youngest faunas of Hansen Bluff (about 

700,000 years). The youngest faunas of Hansen Bluff seem 

nearly as advanced as the type population from the Cudahy 

fauna of Kansas, but these are very small samples from 

Hansen Bluff. 

The Trout Cave No.2 fauna is older than the Cudahy 

fauna (Pfaff, 1990), and, apparently, older than the youngest 

of the Hansen Bluff faunas, although the small samples from 

this part of Hansen Bluff sequence make this comparison 

uncertain. It is younger than the Cumberland Cave fauna and 

than the oldest faunas of Hansen Bluff by virtue of the above 

comparisons. Arbitrarily the Trout Cave No. 2 fauna is 

assigned an age of abo~t 725,000 years. 

These faunal compositions make it seem possible that 

in the faunas of eastern United States: (1) Cheetah Room 

fauna is perhaps 840,000 years old, (2) Hanover Quarry 

Fissure fauna is perhaps 835,000 years old, (3) Cumberland 

Cave fauna is perhaps 830,000 years old (compare van der 

Meulen, 1978, fig. 14, which places it at the same age as 

closely as the time scale can be read), and (4) Trout Cave No. 

2 fauna is, uncertainly, in the vicinity of 725,000 years old. 

Along the east side of the Rocky Mountains, (1) SAM 

Cave (BOT-4locality) is perhaps 875,000 years old (other 

faunas in SAM Cave extend back in time into the Jaramillo 

event and forward into the Brunhes Chron), (2) oldest 

Hansen Bluff is about 820,000 years old, (3) youngest 

Hansen Bluff is perhaps 700,000 years old, (4) the Cudahy 

fauna, out on the Great Plains, has been known for some time 

to be about 610,000 years old, and (5) the age of the Porcupine Cave faunas, south-central Colorado, the highest fossil 

microtine faunas in the United States (9,500 ft), is not 

known, but the presence of immigrant Microtus (from 

Beringia) with the last of endemic M. paroperarius is 

believed to indicate an age of around 450,000 years. 

Although the fossil microtine faunas of the eastern 

United States lack direct external age control, the integration 

of their evolutionary stages with those found in fossil faunas 

of the Great Plains and adjaceflt Rocky Mountains (that do 

have external age control) enables a plausible interpretation 

of the ages of these eastern faunas. Together, the microtine 

faunas of the United States, from the Rocky Mountains to the 

Atlantic coast, indicate and illustrate so explicit a history of 

change in several lineages that the entire region appears to be 

a single faunal region; and anomalous relationships, such as 

the failure of Pitymys and Terricola to coexist, raise the 

question of causes other than provincialism. It is difficult to 

consider greatly different age assignments for the faunas of 

the United States east of the Rocky Mountains. 

The age of Porcupine Cave faunas is based entirely 

upon the presumed age of the immigration of Beringian 

Microtus (see Repenning and others, 1990). In terms of possible error for these "dated" faunas east of the Rocky Mountains, possibly the greatest uncertainty is in the age of the 

BOT -4 fauna of SAM Cave, which is certainly younger than 

the Jaramillo event and older than the immigration of 

Lasiopodomys and Terricola, believed to be about 850,000 

years old. At first this immigration date was based on three 

premises: (1) the immigration came with the first Nebraskan 

ice; (2) the first Nebraskan ice correlates with oxygen isotope stage 22; and (3) oxygen isotope stage 22 is 850,000 

years old. These assumptions appear to be in agreement with 

other evidence of the age of this climatic change around the 

Northern Hemisphere (Repenning, 1984; Repenning and 

others, 1990). 

If the inferred age of the immigration is too old, the ages 

assigned to the Cheetah Room, Hanover Quarry Fissure, and 

Cumberland Cave faunas would be compressed against the 

820,000 year age of the oldest fauna of Hansen Bluff. If the 

inferred age of the immigration is too young, it must be less 

than 50,000 years in error, as the age of the BOT -4 fauna of 

SAM Cave is clearly less than the 900,000 year termination 

of the Jaramillo event and the immigration clearly occurred 

more recently than the BOT -4 fauna. In theoretical averages, 

this would reduce to a margin of error of 10,000 years 

between the ages arbitrarily assigned to the Cheetah Room, 

Hanover Quarry Fissure, and Cumberland Cave faunas, and 

it would also deny what seems to be the most logical stimulus for the dispersal, the climatic change that brought on the 

Ice Ages. All these age assignments have the further qualification that they depend upon the accuracy of radiometric 

ages assigned to the paleomagnetic stratigraphy. 

From the preceding comparisons and inferred ages, it 

would appear that to the east of the Rocky Mountains the last 

of immigrant Lasiopodomys evolved into a primitive Microtus paroperarius about 830,000 years ago (Cumberland 

Cave), which led to typical M. paroperarius between 

700,000 (latest Hansen BlufO and 610,000 years ago 

(Cudahy). The first M. paroperarius population without 

Lasiopodomys variants appears just before the Brunhes 
78 AUOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Chron (820,000 years ago, oldest Hansen Bluff), and it is 

primitive in both first lower and last upper molars; not until 

well after the Brunhes had begun is an advanced M. paroperarius known (high Hansen Bluff, Cudahy, and Trout Cave 

No.2). 

7. The Anza-Borrego Desert, southernmost California, contains the Vallecito Creek faunal succession, from 

which two teeth shown in figure 10 were recovered. Figure 

lOA is clearly of an advanced species of Microtus, and the 

tooth appears inseparable from that of the living Microtus 

californicus, except that "Microtus" enamel-thickness 

differentiation is not so well developed; it has well-formed 

Secondary Wings and shortened Dimension A-A'. 

This specimen, together with a toothless mandible 

whose alveolus indicates the same M/1, is from a locality in 

the Vallecito Creek faunal succession (LACM Loc. 6683). 

This locality is estimated, based on interpolation using a calculated constant sedimentation rate in a continuous section, 

to be 1.5 million years old (360m (1,175 ft) below the base 

of the Brunhes Chron, 109 m (330 ft) above the Olduvai 

event). It may be the oldest "dated" record of Microtus in the 

world, but doubt has been raised about its age in preceding 

discussion (p. 59), and the age has been reduced 100,000 yr 

to allow for presumed hiatuses (Jaramillo not recorded). 

The Irvingtonian I lemming Mictomys anzaensis (very 

similar to the latest Blancan Mictomys vet us) was described 

from this locality (Zakrzewski, 1972) and two other Blancan species, Mimomys parvus and Ondatra idahoensis 

(LACM specimens, unpublished), are also present in this 

and other faunas of this part of the section. These Blancan 

holdovers are typical of the Blancan V microtine age in the 

United States, which is between 2.6 and 1.9 million years 

old, but they are known to have lived into early Irvingtonian 

I faunas. (See section on correlation under the genus Microtus, p. 59-60.) All three are also present after the end of the 

Olduvai event (ending 1.67 Ma) in the Froman Ferry faunas 

(unpublished; present author's data) of the Glens Ferry 

Formation of Idaho (locality 33, fig. 1). 

The Microtus from the Anza-Borrego Desert is remarkably advanced for so ancient a species of the Microtini. It is 

not possible to rationalize this oldest Microtus from the 

Anza-Borrego Desert of California in the perspective of the 

known history of the tribe Microtini in the Northern Hemisphere (fig. 14). It is perhaps 670,000 years older than the 

oldest possible appearance of the primitive Microtus paroperarius in the United States to the east of the Rocky Mountains (Cumberland Cave). It is nearly 800,000 years older 

than the frrst dated M. paroperarius with well-developed 

Secondary Wings (Cudahy fauna), and it is 1 million years 

older than the presumed date of the immigration of AsianBeringian Microtus east of the Rocky Mountains. 

A problem arises with the interpretation of the AnzaBorrego Desert records (see p. 59). Although all published 

descriptions of the paleomagnetic section over the last 

decade and more have presumed the youngest normal event 

to be the Jaramillo, this is an assumption. If the Jaramillo is 

absent in the section and the uppermost normal event represents the Brunhes Chron, as indicated by the presence ofTerricola meadensis (p. 59-60; fig. 1 OB) the age of the oldest 

Microtus would be reduced to about 1.4 million years, 

depending upon how much of the record was missing in 

addition to the Jaramillo event. This would alter the age 

interpretation (fig. 14), but probably not very much. 

Based on other records, the Blancan holdover species 

associated with this early Microtus may be as young as 1.4 

million years. Tectonic history of the region indicates that 

the Anza-Borrego Desert was subjected to uplift that ended 

deposition after the youngest normal polarity recorded 

(Johnson and others, 1984). The specimen of Terricola 

meadensis was from the Vallecito Creek faunal sequence, 

and although the locality was not covered by the paleomagnetic study, it was along strike from deposits that were, and 

it was from the same horizon as several other faunas predating the youngest normal polarity of the magnetic section 

(J.A. White, written common., 1991). It was not from an isolated deposit that might have accumulated later, after uplift 

of the Anza-Borrego Desert. 

Microtus califomicus is also known by a much better 

sample from the Irvington fauna near San Francisco, California: the type locality of the "North American" Irvingtonian 

mammal age (locality 22, fig. 1). Here, the species has associated complex last upper molars and more typical enamelthickness differentiation (fig. lOC). This fauna is found in 

rocks of reversed polarity and is clearly older than the 

Brunhes Normal-polarity Chron, but is not certainly younger 

than the Jaramillo event (0.97 to 0.90 Ma). The Irvington 

fauna, although containing a good sample of Microtus californicus, completely lacks Terricola meadensis, although 

the species is known from other northern California localities, one quite near the Irvington locality (North Livermore 

Avenue locality; Repenning, 1983). This suggests that the 

Irvington fauna is older than 850,000 years and predates the 

immigration of Terricola. 

Even if as young as 850,000 years, the advanced 

Microtus californicus from the Irvington locality would be 

30,000 years older than the very primitive Microtus paroperarius from the lower part of the Hansen Bluff faunal 

sequence of Colorado (fig. 12A), 20,000 years older than the 

Microtus-Lasiopodomys from Cumberland Cave fauna of 

Maryland, and 10,000 years older than the Lasiopodomys 

with some Microtus variations from Cheetah Room of West 

Virginia, all with individuals having a simple last upper 

molar and a much less complicated frrst lower molar. The 

reversely polarized Irvington fauna cannot be as young as 

theM. paroperarius population from Trout Cave that is composed primarily of primitive morphotypes and which 

appears to be about the age of the beginning of the Brunhes 

Chron. It would be about 240,000 years older than the Cudahy fauna of Kansas, in which some individuals of Microtus 

paroperarius assume a morphology as advanced as Microtus 
PROVINCIALITY 79 

califomicus from the Irvington fauna; but the Cudahy population contains some individuals that are far more primitive 

than any individual from the clearly older Irvington sample, 

which has much less individual morphologic variation. 

The sample of Microtus califomicus from the Irvington 

fauna is of good size (65 specimens including several lower 

jaws) and shows very little individual morphologic variation 

in comparison with that shown by the Cudahy fauna. It is a 

population that has polarized its morphologic mode and is 

more removed in time from its ancestor than is the 610,000-

year-old Cudahy population. Thus, more derived species of 

Microtus are known west of the Rocky Mountains from faunas that are at least 240,000 and possibly close to 1 million 

years older than M. paroperarius from the Cudahy fauna of 

Kansas, to the east of the Rocky Mountains. 

This major interprovincial difference in the time of evolution of Microtus is significant, but has not yet been 

described outside the conterminous United States and adjacent southern Canada. As discussed in the consideration of 

Allophaiomys from the Wellsch Valley fauna of Saskatchewan (p. 36--38), the Californian records seem more in 

accord with the eastern Beringian records, which indicate 

that a large variety of both primitive and advanced Microtus 

morphotypes lived at Locality CRH-47 of the Old Crow 

basin during the Jaramillo event. 

The Californian records, the Wellsch Valley record, 

and the east-Beringian records do not correlate with any 

record of the history of Microtus in the United States east of 

the Rocky Mountains before about 450,000 years ago when 

Beringian Microtus, assigned to several living species, first 

appeared in the eastern province of the United States 

(Repenning, 1984, 1987; Bamosky and Rasmussen, 1988). 

Figure 11A illustrates a form of Lasiopodomys also 

from the Anza-Borrego Desert of California that is interpolated to be 1.2 million years old (LACM Loc. 1942; 165m 

below the Brunhes Chron, 304 m above the Olduvai event). 

If the inferred date is correct, this would be the oldest dated 

record of Lasiopodomys in North America. Lasiopodomys is 

also dated as being older than the Jaramillo event in the 

Gongwangling fauna of Shaanxi Province, P.R.C. (An and 

Ho, 1989; Zheng and Li, 1990-as Microtus), and in the 

pages that follow some of the records from the Olyor Suite 

of the Krestovka Sections in Y akutia are shown to be probably this old or older. Older ages of Lasiopodomys in other 

Eurasian faunas are inferred by faunal composition, as mentioned previously (p. 46) in connection with Lasiopodomys 

praebrandtii from the Kudun fauna of Buryat A.S.S.R. 

Finally, when, as well as where, Microtus first evolved 

out of Lasiopodomys is clearly uncertain; that it did so more 

than once in different regions of the world seems obvious. It 

is also probable that Lasiopodomys, the Allophaiomys/ 

Microtus transitional genus, may also have a different age 

significance in these different provinces, and perhaps may 

not have looked quite the same. 

The evolution of Microtus paroperarius out of 

Lasiopodomys to the east of the Rocky Mountains in the 

United States is clearly a provincial and late event. Before 

450,000 years ago the absence of Microtus of Old World 

origin in the eastern province of the United States appears to 

result from climatic conditions (Repenning, 1990); not until 

the Kansan glaciation did this genus of Asian ancestry move 

south of southern Canada; its northern range before this time 

suggests that the eastern United States was too warm during 

the earlier (Nebraskan) glacial advances (Repenning, 1990). 

The Rocky Mountain cordillera of North America has 

always been a barrier to the dispersal of microtine rodents. 

The fauna to the east of these mountains has always differed 

from that to the west, and, lasting until after the Olduvai 

event, two separate dispersal routes have been well documented on either side of the cordillera between Beringia and 

the United States (Repenning, 1987, 1990). No Allophaiomys is known west of the Rocky Mountains at any time, and 

its entry into the United States to the east of these mountains 

appears to have preceded, by nearly half a million years, the 

entry of advanced Microtus to the west. This has a bearing 

on. the time of extinction of Allophaiomys in Beringia. 

Topographically, the Rocky Mountains follow a great 

circle track across Alaska to the Bering Strait. Farther west 

they form the mountains of eastern and southeastern Siberia 

and extend past the Sea of Okhotsk southwest to the region 

of Lake Baikal. They fall in a nearly straight line on a polar 

projection such as used for figure 1. 

Possibly Microtus evolved at an earlier date out of 

Lasiopodomys in China; its earlier evolution from that genus 

seems consonant with the distinctively advanced dental morphology of living and fossil Lasiopodomys in the Oriental 

faunal region. As noted earlier (p. 46), since before the 

Jaramillo event L. brandtioides of China was as advanced as 

morphotypes referred to Microtus in the rest of the Northern 

Hemisphere. 

Possibly these forms dispersed through Beringia to 

North America south of the mountain barrier, without crossing it, thus ending in California still to the "south" of the 

mountain chain. Possibly Chinese Lasiopodomys-Microtus 

crossed the "Rocky Mountains" into northern and western 

Beringia later, and again moved southward in North America on the east ("north") side of the Rocky Mountains. Based 

upon present knowledge, it is equally possible that 

Lasiopodomys evolved into Microtus in Western Siberia 

later than in the Oriental region and moved eastward, north 

of the mountains, through northern Beringia and southward 

on the east side of the Rocky Mountains. The first record in 

the Krestovka Sections is a primitive form, although not the 

most primitive known morphotype, as might be expected in 

either model. 

One is reminded that the single living North American 

species of Microtus that still retains a simple last upper molar 

in the majority of its individuals is Microtus oregonensis, 

which still lives in the Pacific Northwest, west of the Rocky 
80 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

Mountains. This species has a first lower molar that is only 

modestly more advanced than living Lasiopodomys brandtii 

of Transbaikalia (compare fig. 12F with fig. llN). That it 

could show so little change in perhaps 1.5 million years does 

not seem strange when one compares the 1.4 million-yearold Microtus californicus (fig. lOA) with the living species 

(not illustrated). Whatever the history was west ("south") of 

the Rocky Mountains and its topographic extensions, the rate 

of evolution in the descendants of Allophaiomys appears to 

have been much slower after developing a Microtus grade 

than it was in the United States to the east ("north"). 

Regardless of where speculation leads, more needs to 

be learned about provincial histories, dispersal routes, geographic and climatic constraints, and the age of specific 

faunas before it is known where and when Microtus originated. Determining the details of provinciality will explain 

the history throughout the Northern Hemisphere. 

CORRELATION SUMMARY 

The preceding summary of faunas (see also table 1), of 

the relationship of their faunal population elements to each 

other, alld of external time controls associated with some, 

leads to the following interpretations of age. The interpretations are based on the assumption that the United States east 

of the Rocky Mountains has, for the most part, experienced 

faunal changes and faunal evolution as a single microtine 

faunal province. 

Exceptions to this assumption have been noted, such as 

the restriction of native Pitymys to the eastern part of this 

province and the failure of the immigrant Terricola to colonize this area. The unique population characteristics of Allophaiomys from SAM Cave, New Mexico, at 8,900 feet 

(2,728 m) elevation, may have resulted from isolation by 

adaptation to higher elevations. It has been suggested that 

native Pedomys has had an environmental restriction that 

limited its distribution to areas below 7,000 feet (2, 130 m) 

elevation in the western Great Plains and out of areas to the 

northeast that are dominated by arctic air. Little attempt is 

made to explain these exceptions, although possible reasons 

seem evident simply from the consideration of modem distribution patterns. The modem ecologic restrictions of 

Pedomys appear intermediate between those of Microtus and 

those inferred for Allophaiomys. 

Despite these exceptions, the strength of the faunal similarity in most species from the Atlantic Coast to the eastern 

parts of the Rocky Mountains seems to indicate that this 

region did exist as a single faunal province within the United 

States. This similarity justifies the following integration of 

faunal records over this great area to produce a single 

biochronologic history. If true, within this region the following age relationships seem to be approximate but unavoidable conclusions. Their precision may raise some doubt in 

the mind of the reader; never before has such temporal precision been suggested. 

However, as illustrated in the preceding section, faunal 

history is vastly different between the region to the east of 

the Rocky Mountains and that to the west. Faunas to the 

west clearly evolved within an entirely different time frame, 

essentially a million years earlier. As presently known and 

as discussed, the western time frame appears more in accord 

with the less known history of microtine faunas in Beringia 

and Asia, possibly China. 

Outstanding in this review is the realization that the 

extinct species Microtus paroperarius of the United States is 

an endemic product of the eastern United States faunal province, equally as native to the region as Pitymys pinetorum 

and as unrelated to other species of Microtus elsewhere in 

the Northern Hemisphere as P. pinetorum is unrelated to 

Terricola. 

Although clearly a provincial product of endemic evolution out of Lasiopodomys in the eastern two-thirds of the 

United States, early Microtus paroperarius is morphologically indistinguishable (in tooth morphology) from early 

Microtus in Asia and Europe, irrespective of the differences 

in age, ancestry, and geography that exist. 

At present, information about the age of critical faunas 

from Eurasia, information based on evidence of age other 

than stage of evolution, is too weak to detect similarly different times and regions of evolution. Microtine biochronology 

has reached the point at which its time-sensitivity is more 

precise than the assumption of global synchroneity of evolutionary (or extinction) events. 

The interpretation of evolutionary processes is also 

brought into question by this history. Debating whether evolution proceeds gradually or spasmodically seems pointless 

when demonstration of time is too weak to indicate the synchroneity of the evolutionary events compared. Additionally, systematic concepts that are based upon the fossil 

evidence of evolution available 200, 100, or even 25 years 

ago have been made inadequate by the acquisition of new 

evidence. In the present report the concept of a monophyletic 

species has been assumed, but not very well defended. The 

concept of a monophyletic genus, even as here recognized in 

unconventional detail, is, in reality, obviously impossible. 

And the conventionally used genus Microtus, including all 

taxa discussed in this report and represented in figure 14, has 

a very complex history, as has been repeatedly illustrated by 

Jean Chaline. If a genus is supposed to be monophyletic, 

Microtus cannot possibly include so many species and subgenera as Chaline has suggested; it cannot even include all 

the species here recognized in a greatly restricted sense. And 

the concept that a genus-group, or higher, taxon is monophyletic seems as archaic as the concept that species are 

diagnosable by sharply defined morphologic differences. 

Species boundaries, ultimately, must be drawn between 

parent and child. 
CORRELATION SUMMARY 

Table 1. Inferred ages and significant faunal characteristics of 

fossil localities discussed; positioned in temporal sequence by 

evolutionary stages; and availability of external age control 

[In taxa listed: I , bimodal overlap; two taxa, both named. > , variation overlap; one 

taxon, the ftrSt named. - , definition boundary mode, double name. ? , identification 

uncertain. In age control column: • , external age control, varying uncertainty. o , age 

interpreted from fauna. Dispersal events are shown between dashed lines(--)] 

Locality and significant taxa Age, in years B.P. 

(if Ma, so stated) 

Age control 

(symbol) 

United States east of Rocky Mountains 

Porcupine Cave, Colorado 

(last Microtus paroperarius,· Terricola; 

immigration of Beringian Microtus). 

Cudahy, Kansas 

(advanced Microtus paroperarius; 

Terricola; Pedomys). 

High Hansen Bluff, Colorado 

(advanced Microtus paroperarius; 

Terricola). 

Trout Cave No.2, West Virginia 

(Microtus paroperarius; Pitymys; 

Pedomys>Alloplutiomys). 

Low Hansen Bluff, Colorado 

(primitive Microtus paroperarius; 

Terricola). 

Cumberland Cave, Maryland 

(Microtus-Lasiopodomys; Pitymys; 

AllophaiomyS>Pedomys). 

Hanover Quarry Fissure, Pennsylvania 

(advanced ?Lasiopodomys; Pitymys: 

AllophaiomyS>Pedomys). 

Cheetah Room, West Virginia 

(Lasiopodomys>Microtus; Alloplutiomysl 

Pitymys; SynaptomyS>Mictomys). 

County Line, Illinois 

(? Lasiopodomys). 

Immigration Lasiopodomys and Terricola. 

Wellsch Valley, Saskatchewan (Alloplutiomys; 

Beringian Microtus; Phenacomys). 

SAM Cave (BOT-4), New Mexico 

(Alloplutiomys>Lemmiscus,· Mictomys,· 

Phenacomys). 

Wathena, Kentuck, Aries, Kansas; Sappa, 

Nebraska (Alloplutiomys). 

Java, South Dakota (Phenacomys; 

Alloplutiomys; many Blancan holdovers). 

Hansen Bluff core, Colorado 

( Alloplutiomys). 

Immigration Alloplutiomys and 

Phenacomys. 

450,000 

610,000 

700,000 

725,000 

820,000 

830,000 

835,000 

840,000 

840,000 to 

850,000 

850,000 

875,000 

875,000 

1.6 to 1.0 Ma 

1.6Ma 

1.9Ma 

0 

* 

* 

0 

* 

0 

0 

0 

* 

* 

* 

* 

0 

0 

* 

1.9 and 1.4 Ma * and o 

Locality and significant taxa Ase, in years B.P. 

(if Ma, so staled) 

United States west of Rocky Mountains 

Cape Mendocino, Livermore, and Anza- <850,000 

Borrego, California (Terricola; no 

Lasiopodomys). 

Irvington, California (advanced Microtus; no 

Alloplutiomys or Terricola). 

850,000+ 

Anza-Borrego, California ?1.2 Ma 

(one of two oldest d.lted Lasiopodomys). 

Anza-Borrego,Carfor.·la(oldestdatedMicrotus ?1.4 Ma 

[advanced]; many Blancan holdovers. 

Froman Ferry, Idaho 1.4 Ma 

(Phenacomys; many Blancan holdovers). 

Immigration of Microtus and Phenacomys to 

West Coast, U.S.A. 

Beringia 

?1.5 Ma 

Olyor Illb, Yakutia (west Beringia) <750,000 

(Microtus; no Lasiopodomys or Terricola). 

Old Crow Loc. CRH-47, Yukon Territory, 950,000 

east Beringia (Lasiopodomys deceitensis; 

diverse Microtus; Phenacomys; Dicrostonyx 

renidens to D. simplicior; no Alloplutiomys or 

Terricola). 

Olyor llla, Yakutia, west Beringia: Locality 1.1 Ma 

KL~9 (to be discussed) (Lasiopodomys 

deceitensis; Microtus; Dicrostonyx renidens; 

no Allophaiomys or Terricola). 

Cape Deceit, Alaskan Beringia (to be 1.3 to 1.6 Ma 

discussed) (Lasiopodomys deceitensis; 

Predicrostonyx hopkinsi; no Alloplutiomys, 

Terricola, or Microtus). 

Olyor llla, Yakutia, west Beringia: Locality 1.3 to 1.6 Ma 

KL~ (to be discussed) (Lasiopodomys sp., 

Predicrostonyx compitalis; no Microtus, 

Alloplutiomys, or Terricola). 

Other records mentioned 

Gongwangling, P.R.C. (one of two oldest dated 

Lasiopodomys: Allophaiomys). 

Karay-Dubina, Ukraine 

(Lasiopodomys, Terricola/Alloplutiomys). 

Razdolie, Western Siberia (Mimomys, 

Lasiopodomys, ?Terricola; Alloplutiomys). 

Mt. Peglia-2, Italy 

(Alloplutiomys>Lasiopodomys). 

Mt. Peglia-1, Italy 

(Alloplutiomys> Terricola) 

Betfia-2, Romania 

(Alloplutiomys pliocaenicus/Terricola). 

Zuurland, Holland: 

first Microtus 

last Alloplutiomys 

1.2Ma 

?1.3 Ma 

-1.3 Ma 

·1.5Ma 

=1.6 Ma 

... 1.7 Ma 

=970,000 

=1.5 Ma 

81 

Age control 

(symbol) 

* 

* 

• 

* 

* 

* 

• 

• 

* 

0 

* 

• 

* 

0 

0 

0 

0 

• 

* 
82 AILOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Table 1. Inferred ages and significant faunal characteristics of 

fossil localities discussed; positioned in temporal sequence by 

evolutionary stages; and availability of external age controlContinued 

Locality and significant tau 

Zuurland, Holland-Continued 

fmt Allophaiomys 

Huangkan, CKT-18: Beijing, China; 

Tizdar: Krasnodar, Russia 

(oldest dated Allophaiomys). 

Age, in years B.P. Age control 

{if Ma, so stated) (symbol) 

1.9Ma * 

2.0-2.3 Ma * 

AGE OF KRESTOVKA OLYOR AND 

CAPE DECEIT FAUNAS 

OLYOR FAUNA, WESTERN BERINGIA 

Sher and others (1979) subdivided the Olyor Suite 

of the Krestovka Sections, Kolyma Lowlands, Y akutia 

(locality 31, fig. 1), into lower and upper members. 

These they called Ilia and Illb, respectively. They have 

found four microtine faunas in the older Olyor lila, at 

localities KL0-8, KL0-7, KL0-10, and KL0-9, listed 

in increasingly younger order. One quarter of a meter 

above KL0-9, the reversed polarity of Olyor lila 

changes to normal (fig. 2). The identity of the normal 

polarity is the basic question in the difference of opinion 

about the age of the Olyor Suite. Repenning (1984) 

thought it probably represented the Reunion event; Sher 

and others (1979) thought it represented the base of the 

Brunhes Chron. The two interpretations were more than 

1.1 million years apart. 

KL0-8, 5.25 m (17 ft) below the base of normally magnetized deposits, and KL0-9, 0.25 m (10 in.) below the 

normal beds, contain the largest fossil microtine faunas and 

are discussed herein. 

KL0-7, 2m (6+ ft) below the normal beds, is younger 

than KL0-8 but consists in part of reworked fossils. The 

reworked fossils include Hypolagus and Predicrostonyx 

hopkinsi(?); both are otherwise unknown in the Krestovka 

Sections (Sher and others, 1979). Teeth of Plioctomys are 

also found in the older parts of Olyor Ilia, apparently 

reworked from the older Kutuyakh Beds, in which they are 

abundant. 

Throughout the world Hypolagus is replaced by 

Lepus, and this replacement was about 2.0 million years ago 

in North America. Lepus is known from the oldest Olyor 

fauna (KL0-8) as well as younger Olyor faunas. Predicrostonyx hopkinsi, named from the Cape Deceit fauna of 

Alaskan Beringia, is the most primitive known member of 

the collared lemmings. The oldest locality, KL0-8, 

contains the more advanced Predicrostonyx compitalis. The 

genus is unknown from the older Kutuyakh Beds, and P. 

hopkinsi? from KL0-7 is presumed to have been derived 

from unknown depositional units missing in the unconformity separating the Kutuyakh Beds from the Olyor Suite. 

KL0-7 also contains Lasiopodomys sp. and Cromeromys 

sp. cf. intermedius(= Mimomys sp. cf. savini) that probably 

represent contemporaneous faunal elements. Lasiopodomys is not known in deposits older than the Olyor, and 

the form of Cromeromys (C. intermedius) is more advanced 

than that found in the Kutuyakh Beds; but both genera have 

a long temporal range through much of the European Biharian (about 1.9 Ma to 850,000 years old; Lasiopodomys is 

probably no older than 1.5 Main Europe). Cromeromys (or 

Mimomys) intermedius (or savini) has about the same time 

range in the Oriental faunal region, probably not surviving 

so long, and different species of the genus have about the 

same temporal range in North America, although they are 

known from only three localities, Java, South Dakota (Martin, 1990), CRH-47 in the Old Crow basin (R.E. Morlan, 

written common., 1991), and the Cheetah Room fauna, 

West Virginia (Repenning and Grady, 1988). 

KL0-10 (1.25 m (4ft) below the normal beds) contains 

Predicrostonyx compitalis with an advanced last upper 

molar that appears to be transitional into the younger 

Dicrostonyx renidens (Sher and others, 1979). D. renidens 

was found 1 m (3 ft) higher in KL0-9. As described by 

Zazhigin (1976), the Olyor Suite of the Krestovka Sections 

contains nearly the full record of the evolution of collared 

lemmings from the earliest known form of Predicrostonyx 

into the living genus Dicrostonyx. It has been suggested that 

the lineage originated and evolved in arctic Asia, possibly 

farther north in regions now covered by the Arctic Ocean 

(Repenning, 1984). 

LOCALITY KL0-8 

As listed by Sher and others (1979), the small mammal 

fauna of Locality KL0-8 in Olyor Ilia of the Krestovka Sections contains Lepus sp., Ochotona sp., Lemmus cf. obenus 

(=L. cf. sibericus), Predicrostonyx compitalis, Cromeromys 

intermedius, Clethrionomys ex gr. rutilus, and the form that 

is illustrated in figure 15 of the present report. The last two 

taxa listed for KL0-8 are reported from faunas of Western 

Siberia as old as the Odessan age (Zazhigin, 1980). The form 

unnamed above was called Allophaiomys in Sher and others 

(1979) and is called Lasiopodomys in the present report. 

Although KL0-8 is a large fauna by the standards of 

the Krestovka Sections, its sample of the tribe Microtini is 

not sufficiently large to confidently evaluate statistically. 

Five frrst lower molars are shown in figure 15. These have a 

Dimension C-C' greatly reduced so that the dentinal 

confluence between the Primary Wings is almost eliminated: they are members of the tribe Microtini. Dimension 

B-B', between the Primary Wings and the Cap, varies from 
AGE OF KRESTOVKA OLYOR AND CAPE DECEIT FAUNAS 83 

c D 

A B 

F G 

0 1 2mm 

E 

Figure 15. Lasiopodomys sp. from the Olyor Suite, member llla, Locality KL0-8, Krestovka Sections, Y akutia. Dimension 

C-C' is nearly closed in all first lower molars (A-E). Dimension B-B' is not reduced in A and D. There is no Dimension A-A'. 

M\3s are simple (F, G). Note that the Posterior Loop on F is reduced as in living Phaiomys leucurus (fig. 4). GIN specimens. 

unreduced to moderately reduced; and Dimension A-A', 

producing Secondary Wings, is not evident: they are members of the genus Lasiopodomys. All last upper molars in 

the sample are simple, and "intermediate" enamel-thickness 

differentiation is dominant. 

Nothing in the sample resembles Allophaiomys pliocaenicus, nor Allophaiomys from other faunas described 

above. All individuals from KL0-8 belong in the tribe 

Microtini, as they have a significant reduction of Dimension 

C-C'. The specimens in figure 15 appear identical to those 

referred to as "Microtus ex gr. oeconomus" by Markova 

(1982) from the Karay-Dubina fauna of Ukraine (illustrated 

in fig. l6F-H, which are reproduced from Markova, 1990), 

and the genus Lasiopodomys, as herein defined, is obviously 

indicated. There is no suggestion of a posterolingual angularity on the Cap as found in advanced species of 

Lasiopodomys, nor is there any indication of a complex last 

upper molar in the sample. 

The morphology of Lasiopodomys found in Locality 

KL0-8 includes individuals with a very large Dimension 
84 AILOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

B-B' (fig. 15A, D). This condition is not a frequent character of known populations of Lasiopodomys, although a few 

individuals in some populations may show a very wide 

Dimension B-B'; three (1.7 percent) are present in the 

Cumberland Cave population of Microtus-Lasiopodomys, 

apparently the youngest record of "typical" Lasiopodomys 

morphotypes. 

In typical Allophaiomys pliocaenicus from Betfia-2, 

the modal condition of Dimension B-B' is narrower. Nearly 

all the specimens shown in figure 11 have a greater reduction 

of Dimension B-B' than do two of the five first lower molars 

from KL0-8 that are shown in figure 15. Comparison with 

Lasiopodomys deceitensis, shown in figure 17, suggests that 

the less marked reduction of Dimension B-B' of Lasiopodomys from KL0-8 may be significant, as it is not found in 

the Alaskan sample. 

Although the significance of this large Dimension B-B' 

is not certain, it suggests a primitive condition, and that possibly this sample should not be assigned to Lasiopodomys 

deceitensis. It is here referred to Lasiopodomys sp. The 

changes upsection into Lasiopodomys of Locality KL0-9 of 

the Krestovka Sections are in the direction of Lasiopodomys 

deceitensis. 

Largely because of its stratigraphic position below 

KL0-9 (whose age is discussed next), and because of the 

apparent change of Lasiopodomys toward a morphotype 

more typical of Lasiopodomys deceitensis in the younger 

KL0-9 locality, the KL0-8 fauna is believed to be younger 

than the Olduvai event (younger than the Kudun fauna of the 

Lake Baikal area) but older than KL0-9. It is inferred to be 

between 1.3 and 1.6 million years old. At present, there is 

insufficient evidence to be more precise. 

LOCALITY KL0-9 

As listed by Sher and others (1979), Locality KL0-9 of 

Olyor Ilia, 5 m (16ft) higher in the Krestovka Sections than 

KL0-8 and '1/4 m (10 in.) below the normally magnetized 

deposits, contains essentially the same fauna as Locality 

KL0-8 except that Dicrostonyx renidens replaces Predicrostonyx compitalis and a species with a Microtus morphotype is present. 

Again, the genus Lasiopodomys is present, as indicated 

by the closure of Dimension C-C'; this dimension is slightly 

more closed than in the sample from KL0-8. Dimension 

B-B' is consistently reduced in comparison with the sample 

from KL0-8, and the use of the species name Lasiopodomys deceitensis seems justified at Locality KL0-9. Not 

only did the lineage of Dicrostonyx undergo evolutionary 

advancement between the localities KL0-8 and KL0-9 of 

Olyor Ilia in the Krestovka Sections, but so did the lineage 

of Lasiopodomys. 

No specimen has a suggestion of the presence of 

Dimension A-A', and all last upper molars, with one exception, are simple; an advanced stage of Lasiopodomys evolution toward the Microtus morphotype is not indicated. In 

contrast, an individual with "Mimomys" enamel-thickness 

differentiation was in the sample of Lasiopodomys (fig. 

16A); but the variability of this character is such that it is difficult to decide the significance of the occurrence. 

The surprising addition to the fauna from KL0-9 is five 

first lower molars with a Microtus morphotype, noted by 

Sher and others (1979). Like Lasiopodomys deceitensis from 

the fauna, these have Dimension C-C' closed, but Dimension B-B' is either narrow or essentially closed, and the teeth 

also have a moderate development of Dimension A-A' on 

the first lower molar (fig. 16D). These five first lower Microtus molars also contrast with those of Lasiopodomys in that 

they alone have "Microtus" enamel-thickness differentiation. The sample of Microtini from KL0-9 may be the only 

one in the world that has all three variations of enamelthickness differentiation. 

One complex last upper molar (fig. 16E) was in the 

sample and is presumed to belong with the first lower molars 

that have a Microtus morphotype. This is not the most primitive Microtus morphotype included in the genus as here 

defined, and it is reasonable to suppose that all individuals of 

Microtus had a complex last upper molar. 

Unlike the Lemmiscus morphotypes from the SAM 

Cave faunas of New Mexico, the Microtus frrst lower 

molars from KL0-9 resemble those of primitive Microtus 

paroperarius populations from the older faunas of Hansen 

Bluff, Colorado (fig. 12A), and the most advanced morphologies of Microtus paroperarius-Lasiopodomys deceitensis 

from the Cumberland Cave fauna of Maryland (van der 

Meulen, 1978, his fig. liD). The Microtus morphotypes 

from KL0-9 would be an expectable variation of advanced 

Lasiopodomys, such as shown from the Hanover Quarry 

Fissure fauna, Pennsylvania (fig. IlL, M), and they are similar to simple Microtus morphotypes from Locality CRH--47 

of the Old Crow basin of Canada. In Europe such Microtus 

first lower molars would be referred to as "nivalid" or 

"arvalid" morphotypes and would be named on the basis of 

their morphologic similarity to a better known taxon, such 

as Microtus nivaloides or Microtus arvalidens, names based 

upon the similarity of their Anteroconid Complexes to those 

of the living species M. nivalis and M. arvalis. Such an identification would be made with the reservation that the taxon 

might not be identical or closely related. 

The preceding comparisons indicate that the simple 

Microtus morphotype cannot be identified as a particular 

species without a much better understanding of the provincial history represented by the compared examples. Nor can 

they be identified without an analysis of the populations. 

The morphotypes of primitive Microtus look very similar 

whether they have evolved in North America or Eurasia. 

Most certainly, the simple morphotypes from the Olyor Suite 

are not primitive M. paroperarius on biogeographic 
AGE OF KRESTOVKA OL YOR AND CAPE DECEIT FAUNAS 

B c D 

0 1 2mm 

Figure 16. Lasiopodomys and Microtus. A-C, first lower molars of Lasiopodomys deceitensis (referred to as "Allophaiomys cf.pliocaenicus" in Sher, 1986) from Olyor Illa Locality KL0-9, Krestovka Sections, Yakutia. F-H, Lasiopodomys 

ratticepoides referred to as "Microtus ex gr. oeconomus" in Markova, 1982, and in Sher, 1986) from the Karay-Dubina 

fauna, Ukraine. D, E, Microtus sp. from KL0-9, first lower and last upper molars. Dimension C-C' is closed or substantially closed in all first lower molars. Dimension B-B' is variably reduced in all individuals. Dimension A-A' is weakly 

present in D, and this is a Microtus morphotype. All M\3s from KL0-9 are simple except that shown as E, which presumably is also Microtus. A has "Mimomys" enamel-thickness differentiation. D has "Microtus" enamel-thickness differentiation. A through E are GIN specimens. F, G, and Hare reproduced from Markova (1990). 

85 

grounds, although on morphologic grounds they could be 

matched with individuals of this species. It would be reasonable, on biogeographic grounds, to consider them as the 

same species as similarly primitive forms from the Old Crow 

basin of Canada, but these have yet to be described and 

named by R.E. Morlan (written common., 1991). 

The associated Lasiopodomys from KL0-9 is not 

advanced; the limited sample shows no variation toward a 
86 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

Microtus morphotype such as is seen in the Cheetah Room 

fauna of West Virginia (fig. llJ, K; also Repenning and 

Grady, 1988, fig. 4E). It appears to equal the advancement 

of Lasiopodomys deceitensis from the Cape Deceit fauna of 

Alaska, and could be described as "typical," with no individual variation approaching the morphology of either Microtus 

or Allophaiomys. No morphotype similar to those few from 

Hanover Quarry Fissure, Pennsylvania (fig. IlL, M), or to 

the advanced Lasiopodomys morphotypes of MicrotusLasiopodomys from Cumberland Cave, Maryland (van der 

Meulen, 1978, fig. llA, F, and G), is present in the Olyor 

Suite. 

The sample size from KL0--9 is too small to statistically state that the Microtus morphotypes of the population 

either have . or do not have overlap of dental morphology 

within the population of Lasiopodomys deceitensis; nor can 

the presence of one or two genera be statistically demonstrated. However, the morphotypes of Lasiopodomys from 

the KL0--9 fauna show no suggestion of gradation between 

Lasiopodomys and Microtus. The presence of a Dimension 

A-A' is not suggested on any specimen of Lasiopodomys, as 

it is in a few individuals of typical Lasiopodomys deceit ens is 

from Cape Deceit, Alaska (fig. 17A) or in 25 percent of the 

population from the Cheetah Room fauna, West Virginia 

(fig. 111-K). And the associated Microtus morphotypes, 

although primitive, are not borderline, and have no individuals that approach a Lasiopodomys morphotype. 

In the Microtus paroperarius-Lasiopodomys deceitensis population from Cumberland Cave fauna, Maryland, in· 

which the morphologic mode of the frrst lower molar falls 

very close to the defined boundary between Lasiopodomys 

and Microtus, 68 percent of the individuals are morphologically intermediate between the conditions shown by the 

Lasiopodomys and the Microtus morphotypes from Locality 

KL0--9. It would seem, if the KL0--9 sample was of an 

intergrading population, that some specimens would show a 

suggestion of having an intermediate morphology. 

In addition, "Microtus" enamel-thickness differentiation is unknown in Lasiopodomys deceitensis from KL0--9; 

in fact, one specimen has "Mimomys" differentiation. But 35 

percent of the Lasiopodomys morpho types from the Cheetah 

Room population have "Microtus" differentiation and, in the 

"borderline'' population from Cumberland Cave, 56 percent 

of the Lasiopodomys morphotypes and 71 percent of the 

Microtus morphotypes have "Microtus" enamel-thickness 

differentiation. 

Although the evolution of enamel-thickness differentiation is difficult to interpret, it does seem to parallel the 

development of other characters, while maintaining wide 

individual variability. Therefore, because the Lasiopodomys morphotypes lack (1) "Microtus" differentiation and 

(2) overlap of Microtus dental morphology, and because 

the Microtus morphotypes lack (3) "intermediate" enamelthickness differentiation and ( 4) overlap of Lasiopodomys 

dental characters, it is difficult to believe that a single, 

endemic population, intergrading between Lasiopodomys 

and Microtus, is represented in Locality KL0--9. 

Thus, the conclusion of Zazhigin (in Sher and others, 

1979, p. 49) seems reasonable: the appearance of Microtus 

in KL0--9 represents an immigration of true, but primitive, 

Microtus from some other Asian area, and does not represent variation within a single, endemic population of 

Lasiopodomys. 

Although the Lasiopodomys fauna of Beringia is still 

not well known, there is no evidence that it evolved into 

Microtus in this region; and primitive Microtus seems to 

have immigrated from elsewhere in Asia into western 

Beringia just before the recorded normal polarity of the 

Olyor Suite. The question of where Microtus came from is 

not yet answerable, although the Oriental faunal region had 

been suggested (p.79). 

More can be said about the question of what polarity 

event is represented by the normal deposits closely overlying 

the immigrant Microtus sp. and endemic Lasiopodomys 

deceitensis. Allophaiomys is not present in the Olyor fauna, 

nor in any known Beringian fauna, but it dispersed to North 

America at the beginning of the Olduvai Normal-polarity 

Subchron; consequently the beginning of normal polarity in 

the Olyor Suite seems not to be the beginning of the Olduvai 

event; the associated fauna contains no Allophaiomys but 

does contain its descendants Lasiopodomys and Microtus, 

both of which have no certain record as old as the Olduvai. 

Furthermore, the beginning of the Olduvai was a very warm 

period in the Northern Hemisphere and the beginning of the 

normal polarity in the Krestovka Sections was the coldest 

period recorded in that section (Repenning and Brouwers, 

1992). 

Faunal considerations also do not favor correlating the 

oldest normal polarity of the Krestovka Sections with the 

base of the Brunhes Chron. These considerations include the 

lack of Terricola in the Olyor, a genus that dispersed to 

North America (through Beringia) less than 100,000 years 

before the Brunhes began. Microtus is abundant (with 

Lasiopodomys) during the Jaramillo event in the Old Crow 

basin of eastern Beringia, but not present in the oldest fauna 

of the Olyor and present only as a primitive form in the 

youngest reversely polarized Olyor 25 em below the polarity 

change; if the first normal polarity were the Brunhes, one 

would expect a more diverse Microtus fauna. Lasiopodomys 

was the abundant microtine of the Olyor, yet it became 

extinct about 35,000 years before the Brunhes Chron in the 

United States. Finally, Sher and others (1979) reported the 

change from Predicrostonyx compitalis to Dicrostonyx 

renidens within 1.25 m (4ft) below the polarity reversal in 

the Olyor, and R.E. Morlan (written commun., 1991) 

reported the evolutionary change from D. renidens into D. 

simplicior during the Jaramillo event in Locality CRH-47 of 

the Old Crow basin. The evolution of D. simplicior out of D. 

renidens during the Jaramillo event seems to eliminate the 
AGE OF KRESTOVKA OL YOR AND CAPE DECEIT FAUNAS 87 

possibility that P. compitalis could evolve into D. renidens 

after the Jaramillo and just before the Brunhes Chron. 

Faunas in the Old Crow basin other than CRH-47 that 

also contain Lasiopodomys and an even greater diversity of 

Microtus than Locality CRH-47 (Morlan, 1984) appear to be 

stratigraphically younger, but are also in normally magnetized deposits. These suggest that the fauna of Locality 

CRH-47 may have lived early during the Jaramillo event. 

Particularly if Locality CRH-47 represents the older 

part of the Jaramillo event, it is difficult to imagine that the 

normal polarity 25 em (10 in.) above Locality KL0-9 is the 

beginning of the Jaramillo event. In the record of the United 

States east of the Rocky Mountains, Microtus paroperarius 

took at least 290,000 years to evolve from a stage of evolution comparable to that in Locality KL0-9 (in the Cumberland Cave fauna) into an advanced condition (in the Cudahy 

fauna of Kansas), comparable to the Microtus population 

found in the Old Crow Locality CRH-47, in early Jaramillo 

deposits. The Jaramillo event was only 70,000 years long, 

and, from this comparison, the stage of evolution represented by Microtus from KL0-9 would suggest that the 

overlying normal polarity was perhaps 130,000 years older 

than CRH-47, deposited during the Jaramillo eventperhaps during the earliest part of the Jaramillo. 

Although not consistent with other hemispheric 

records, the earliest record of Microtus from southern 

California indicates that a dispersal of this genus through 

Beringia must have taken place possibly 1.5 million years 

ago, 500,000 years before the Jaramillo event. The record 

does not indicate that the dispersing Microtus passed, en 

route, through the Kolyma Lowlands, where the Krestovka 

Sections are located, to be present in Locality KL0-9. 

Dispersal at this time is recorded only west of the Rocky 

Mountains in the United States, and it may also have been 

restricted to Magadan, in the lowlands east of the Kolyma 

Range, the "west side of the Rocky Mountains" as they 

project into Asia. Possibly this region was the source of the 

first Microtus in Locality KL0-9, via crossing the Kolyma 

Range. 

The greatest objection to a correlation of the first 

normal polarity in the Krestovka Olyor Suite, 25 em (10 in.) 

above the frrst Microtus, with the Jaramillo event comes 

from the consideration of the climatic record. Sher and 

others ( 1979) reported a major decrease in arboreal pollen 

("almost absent") and an increase in pollen of grass and cold, 

dry-climate plants in the horizon of Locality KL0-9. The 

cold and dry period continues upward into the normally 

polarized deposits. The flora of KL0-9, continuing through 

the change to normal polarity, indicates a steppe-tundra 

environment, and the coldest climate recorded in the 

Krestovka Sections. The locality is now in boreal forest, a 

less severe climate than indicated in this part of the Olyor 

Suite. 

An inconsistency is evident when this increase in 

climatic severity in the Krestovka Sections is compared with 

the pollen record of the type Olyor Suite, 150 kilometers (93 

mi) to the north. Unlike the Krestovka Sections, the type 

section of the Olyor Suite is now in full and widespread 

tundra. The type section begins below the Jaramillo event 

and continues into reversed deposits above this event (Virina 

and others, 1984). 

During the period of normal polarity that is assigned to 

the Jaramillo event in the type section, the percentage of 

shrub and arboreal pollen was no lower than 20 percent and 

was mostly well above this figure (Giterman and others, 

1982); the pollen spectrum changes little throughout the type 

section. The lack of evidence of a severe cold and dry climate just before and during the Jaramillo event in the type 

section casts considerable doubt on the correlation of this 

event to the normally polarized deposits, containing pollen 

indicating climatic severity, recorded in the frrst normally 

polarized deposits of the Krestovka Sections 150 km to the 

south. 

The inconsistency is present in other records in addition 

to the type section of the Olyor Suite. The eastern Beringian 

Locality CRH-47 of the Old Crow basin, which contains 

diverse morphotypes of Microtus, also dates from the 

Jaramillo event; like the type section of the Olyor Suite, its 

pollen record indicates a climate like that of today or 

'possibly slightly warmer (J.V. Matthews, Jr., oral common., 

1987). In Holland, Zagwijn and de Jong (1984) described the 

Bavelian floral age, a warm age that begins just before the 

Jaramillo event and ends shortly after it. (Microtus first 

appears in Holland during the Bavelian according to van 

Kolfschoten, 1990.) In southern Canada, Churcher (1984) 

inferred that the Wellsch Valley fauna lived in a warm 

climate, and, as discussed previously (p. 37), this fauna probably lived shortly after the Jaramillo event. In core 644 in the 

Norwegian Sea (Jansen and others, 1988) and in CESAR 

core 14 on the east end of the Alpha Cordillera of the central 

Arctic Ocean (Scott and others, 1989), the Jaramillo event is 

marked by a warm period. The author is aware of no records 

during the Jaramillo event that indicate pronounced cold. 

About a half meter ( 11/2 ft) above the base of the normally polarized deposits in the Krestovka Sections, Sher and 

others (1979) reported a thin interval of reversed polarity. 

This was initially indicated by a single determination in 

uncleaned samples but appears, in Sher and others (1979, fig. 

6), to be indicated by three samples after cleaning. These 

polarity determinations suggest the possibility that the 

deposits having the oldest normal polarity and the coldest 

climate in the Krestovka Sections may be only about onethird meter thick. The presence of these higher reversed 

samples has not been considered significant, but it seems 

possible that the oldest normal polarity of the Krestovka Sections represents a brief event before the Jaramillo Subchron. 

The Cobb Mountain Normal-polarity Subchron was 

identified by Mankinen and others (1978) and may be the 

most securely dated short polarity reversal of the late 

Matuyama and Brunhes Chrons (Champion and others, 
88 AUOPHAIOMYS AND THE OL YOR SUITE, YAKUTIA 

1988); it is 1.10±().02 million years old (Mankinen and 

GroJDin6, 1982). Although possibly lasting less than 10,000 

years (Champion and others, 1988), but possibly as much as 

25,000 years (Clement and Kent, 1986), the Cobb Mountain 

is a completely normal event within the Matuyama Chron 

and, where found, is unambiguous. According to Mankinen 

and Gromme (1982) it has been identified in the Caucasus 

region of southern Russia (Kvemonataneby excursion), in 

the Melanesian region of equatorial Pacific, in Japan (Komyoike event), across the East Pacific Rise ("A" event), in the 

eastern Caribbean, and in California, U.S.A. 

Although they did not report detecting the Cobb Mountain event, Jansen and others (1988) reported that at site 644 

in the Norwegian Sea a transition to major glacial activity of 

the Scandinavian Ice Sheet began 1.2 million years ago, and 

they showed a pronounced peak in activity at 1.12 million 

years ago. This peak would have occurred during the 

Menapian cold flora of Holland, before the warmer Bavelian 

flora that centers on the Jaramillo event. 

Also, in CESAR core 14 at the east end of the Alpha 

Cordillera in the Arctic Ocean, Scott and others (1989) 

reported a major change to periods of perennial ice cover 

(with one brief exception more than 2 million years ago, 

their first record of perennial ice in the Arctic Ocean) beginning with a pre-Jaramillo normal-polarity event. These 

periods of perennial ice cover decreased dramatically during 

the Jaramillo and then increased again after this event. Scott 

and others (1989) assigned the normal polarity at the 

beginning of the intermittent perennial ice record to the Gil sa 

event (about 1.64 to 1.63 Ma), but this assignment results in 

unusually rapid rates of sedimentation between the normal 

event and the Olduvai. An assignment to the Cobb Mountain 

event would reduce inferred sedimentation rates between the 

event and the Olduvai to within the limits they calculated for 

the entire core. In addition, assignment of the event to the 

Cobb Mountain would correlate the beginning of periodic 

perennial ice cover on the central Arctic Ocean with the 

beginning of major Scandinavian glacial activity. 

The first brief period of deposition (0.3-0.5 m; 12-19 

in.) during normal polarity in the Olyor Suite of the 

Krestovka Sections, included within that part of the section 

having evidence of the most severe climate recorded in the 

Krestovka Sections, is here correlated with the beginning of 

intermittent perennial ice cover of the Arctic Ocean reported 

in CESAR core 14, with the beginning of intense activity of 

the Scandinavian Ice Sheet reported in the Norwegian Sea at 

Site 644, with the Menapian cold flora of Holland, and with 

the Cobb Mountain Normal-polarity event ( 1.10 million 

years old) (Repenning and Brouwers, 1992). 

The normal-polarity event recorded in the 0.3-0.5-mthick part of the Krestovka Sections is assigned to the Cobb 

Mountain event and not the Jaramillo event, which is not 

marked by evidence of extreme cold in the type section of 

the Olyor Suite, nor in other areas of the Northern Hemisphere. This interpretation of the polarity of the section is 

also in agreement with the difference between the lowvariety Microtus fauna of Locality KL0-9 in western Beringia and Jaramillo-aged, high-variety-of-Microtus-morphotypes fauna at Locality CRH-47 in eastern Beringia, as 

judged by the rate of morphologic change of Microtus 

paroperarius in the United States. 

The beds with normal polarity in the uppermost part of 

the Olyor Suite of the Krestovka Sections (above the three 

reversed samples and assigned to Olyor lllb) may represent 

the Jaramillo event or the Brunhes Chron, or both; the small 

samples (A.V. Sher, oral commun., 1990) of the microtine 

faunas present in Olyor Illb are not diagnostic of population 

characteristics, but they contain Microtus and Dicrostonyx 

(Sher and others, 1979). 

If this correlation of the short normal interval in the 

Krestovka Sections, containing the coldest flora of the 

Krestovka Sections, is correct, then the climatic disagreement between it and the oldest normal polarity of type Olyor 

Suite (and with Canadian Locality CRH-47) no longer 

exists, and the interpretation is in agreement with evidence 

of increasing cold at that time in the central Arctic Ocean, in 

the Norwegian Sea, and in the fossil flora of Holland. The 

age of Locality KL0-9 of Olyor Ilia would then be very 

close to 1.10 million years. 

By polarity control, the age of the oldest fauna of the 

Krestovka Olyor, KL0-8, would be then older than 1.10 Ma, 

and, by biochronologic control, younger than Lasiopodomys 

praebrandtii in the Kudun fauna south of Lake Baikal; that 

is, Locality KL0-8 is younger than the Olduvai Normalpolarity Subchron ending 1.67 million years ago based on 

the age of the Kudun fauna inferred from faunal composition, and on the lack of normal polarity in the oldest part of 

Olyor lila. 

THE CAPE DECEIT FAUNA, ALASKA 

The Cape Deceit fauna of the Seward Peninsula, 

Alaska, was described by Guthrie and Matthews ( 1971 ). 

The locality is on the east side of Cape Deceit about 1.8 

miles (3 km) northwest of the village of Deering. It was 

found in bluffs exposed along the shore of Kotzebue Sound 

of the Chukchi Sea. The locality is near lat 66° N. and now 

has a shrub tundra flora. Matthews (1974) has reviewed the 

fluctuating environments represented in the deposits, which 

were, alternately, both colder and warmer than today. The 

fauna contains Lasiopodomys deceitensis, Predicrostonyx 

hopkinsi, Phenacomys deeringensis, and Lemmus sp. cf. L. 

sibericus and was found in deposits recording the coldest 

environment recognized by Matthews. Matthews (1974) has 

inferred that deposition ended with a warm spell much 

warmer than today. Permafrost in the deposits thawed, with 

resulting erosion. 

No external evidence of the age is available, and the 

fauna has been considered as being about the same age as 

Olyor Ilia from the Krestovka Sections, because of faunal 
AGE OF KRESTOVKA OL YOR AND CAPE DECEIT FAUNAS 89 

similarity. Accordingly, its age is revised along with that of 

the Olyor. 

The Cape Deceit fauna has a fair-sized sample of 

Lasiopodomys deceitensis (29 M/1), as well as some other 

types of microtines, and the fauna appears large enough to 

have included some Microtus if they were present in the 

area. Neither the Cape Deceit fauna nor the KL0-9 fauna 

has a Lasiopodomys-Microtus population as does the Cumberland Cave fauna, nor do they contain individuals of 

Lasiopodomys with a variation approaching a Microtus morphotype; Microtus was not evolving out of these Beringian 

populations. Although both are in the Beringian faunal province, Locality KL0-9 of the Krestovka Sections contains 

immigrant Microtus, which is missing in the Cape Deceit 

fauna, and a more advanced collared lemming than in the 

Cape Deceit fauna; both indicate that the Cape Deceit fauna 

is older than Locality KL0-9. 

A contradiction may exist regarding the correlation of 

the Cape Deceit fauna of Alaska with the KL0-8 fauna of 

Olyor Ilia in Krestovka Sections. As has been noted, Locality KL0-8 contains some individuals of Lasiopodomys sp. 

(fig. 15) that are possibly more primitive than L. deceitensis 

from the Cape Deceit fauna (fig. 17) in that the KL0-8 

sample has a Dimension B-B' that is conspicuously large. 

However, Predicrostonyx compitalis from KL0-8 is more 

advanced than Predicrostonyx hopkinsi from Cape Deceit. 

The inconsistency may indicate a dispersal delay of 

collared lemmings from western to central Beringia, or it 

may indicate too small a sample of the Predicrostonyx 

population from KL0-8, as specific identification depends 

upon the average condition of the population (Zazhigin, 

1976; Agadzhanyan, 1976; Gromov and Polyakov, 1977). 

Conversely, the suggestion of the inferred primitive nature· 

of Lasiopodomys from KL0-8 may not be correct. Both 

arguments are weak because of small samples and resulting 

misinterpretation. 

Tentatively, the Cape Deceit fauna is considered to be 

of about the same age as KL0-8, but because of the uncertainty of the two conflicting interpretations the fauna is 

assigned an age span, rather than a specific age approximation. It is inferred that its age is between 1.3 and 1.6 million 

years-the same age range that is inferred for KL0-8. The 

Kudun fauna of the Lake Baikal area has a more primitive 

species of Lasiopodomys and is believed to date from the 

Olduvai event (ending 1.67 Ma). A more precise age interpretation is not possible without a better record of microtine 

history in Beringia and adjacent Asian faunal regions. If the 

deposits containing the Cape Deceit fauna have a normal 

polarity, this could only represent the Olduvai event, and the 

inferred age of Lasiopodomys praebrandtii from the Kudun 

fauna would have to be considered either the age of the early 

part of the Olduvai event, or older, unless greater detail is 

learned of the provincial histories involved. 

CONCLUSION 

Global history has been ignored in the previous use of 

the biochronology of microtine rodents. Similar evolutionary and extinction events, that in fact were local in extent, 

have been considered synchronous around the world. This 

has resulted in frequent errors in age interpretation. Such 

errors cannot be avoided without the aid of dated provincial 

histories and without knowledge of interprovincial 

dispersals. 

The number of errors has been increased by the use of 

different taxonomic systems by various researchers, and by 

reliance on faunal lists for correlation without consideration 

of the classification system of the person who compiled the 

faunal list. By no means the only example, but as discussed 

in this report and shown in figure 16, what Markova called 

Microtus, Zazhigin called Allophaiomys and Repenning 

called Lasiopodomys. The present author had assumed that 

these specialists were in agreement on their classification; 

the offices of Zazhigin and Markova are little more than a 

long stone's throw apart. 

The present author also thought that he could infer relationships on the basis of Markova's (1982) illustrations of 

her specimens and Zazhigin's listing of taxa (Sher and 

others, 1979). Thus the author's 1984 assessment of the age 

of Olyor Ilia of the Krestovka Sections was based upon the 

erroneous assumption that the same taxonomy was being 

used by the two different authors; this same erroneous 

assumption was made by Sher and others (1979) and Sher 

(1986), and seemed (in the past) to the present author to confirm his opinion. 

The present report was written to illustrate how the 

biochronology of the microtine genus Allophaiomys, and 

those genera derived from this genus, is complex and 

asynchronous on a global scale, and also to demonstrate how 

the interpretation of the age of any fossil locality that is 

based upon this biochronology cannot be convincingly made 

across provincial boundaries without knowledge of the history of these lineages within each province of concern. 

However, with this knowledge or within a single faunal 

region, it is shown that a biochronology can be developed 

with a temporal resolution that approximates a precision of 

5,000 years. 

The greatest weakness of this precision is that currently 

there is no known external method of determining geologic 

age that could be used to check such temporal resolution. It 

must be emphasized that between points of external age control the age assignments given are interpolations. Because 

they are applied to single lineages over short time periods, 

these interpolations are less likely to incorporate greater 

error than other methods of geologic age interpolation 

between dated events, such as between control points in 

geopolarity stratigraphy. 
90 AUOPHAIOMYS AND THE OLYOR SUITE, Y AKUTIA 

A 

B 

D c 

0 1 2mm 

E 

F 

Figure 17. Lasiopodomys deceitensis from Cape Deceit fauna, Alaska. A through Dare first lower molars; E and 

Fare last upper molars. Dimension C-C' is closed or nearly so in all first lower molars. Dimension B-B' is reduced 

in all individuals. Dimension A-A' is not present, although B shows a weak suggestion of a buccal Secondary Wing. 

M\3s are simple and F is little worn. This population of Lasiopodomys is considered "typical," and B most nearly 

approaches a Microtus morphotype. None approach a Pitymys or Terricola morphotype as Dimension C-C' is 

closed. 

However, that rates of evolution are more constant than 

rates of sediment deposition has not been established. The 

example of the history of what all concerned would call 

Microtus on either side of the Rocky Mountains in the 

United States illustrates the point that a single lineage must 

not be assumed because the taxa look alike and have been 

assigned to the same genus. Mention has been made (p. 78) 

of the slight change in Microtus californicus between the 

earliest record of the genus about 1.4 million years ago and 

living Microtus californicus on the west side of the Rocky 

Mountains; and of the evolution of the "same" genus from a 

Lasiopodomys morphotype to a characteristic Microtus morphotype in 220,000 years on the east side of this mountain 

barrier. These must be considered different lineages even 

though they are placed in one genus; obviously the two lineages have different biochronologic significance. And this is 

but the first clue to the diversity of Microtus on a worldwide 

basis. 

In addition, the accuracy of the Allophaiomys-anddescendant biochronology, when used across regional faunal 

boundaries, depends upon the interpreter's familiarity with 

the global history of the organisms involved. 
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A 

Academy of Sciences of the U.S.S.R., 

Moscow ............................................................. 2,4 

AcknowledgDlents ....................................................... 4 

Acronyms .................................................................... 4 

AllopluJiomys ................................................... 2, 13, 25 

guildayi ....................................................... 52, 68 

laguroides ...••......••........•••..........•••..•......•.........• 10 

pliocaenicus ...................................... 5, 10, 13, 23 

1 Ma in North America ....................................... 7 

anceslral genus .................................................. 22 

differences in definition .................................... ,. 7 

in Olyor ............................................................... 5 

no Beringian record ............................................ 7 

oldest records .................................................... 22 

provincial extinction ......................................... 62 

replaced by Microtus .......................................... 5 

temperate to subtropical .........•...................... 6, 64 

type ............................•...................................... 24 

variation ...................................................... 17, 25 

Allophaiomys/Lasiopodomys in Eurasia ................... 50 

Alpha Cordillera, Arctic Ocean .................................. 7 

Anza-Borrego Desert .................. 32, 38, 51, 59, 72, 78 

Arboreal vegetation reduction, Begunov and 

Kutuyakh ................................................... 2 

Arctic Ocean Borderland .................................... 1, 2, 6 

Arvicola enamel thickness .........•.............................. 11 

Arvicolinae, Subfamily ....................................... 21, 24 

Arvicolini, Tribe ........................................................ 21 

B 

Bavelian, Holland ................................................ 30, 88 

Beds (Russian usage) .................................................. 2 

Begunov Suite, Pliocene ............................................. 2 

Beringia .............. 2, 4, 7, 19, 31, 36, 37, 44, 51, 53, 55, 

59, 62, 75, 79, 82, 86, 89 

lack of Terricola, AllopluJiomys .•.....•................ 72 

Microtus ............................................................ 60 

Biochronology ............................... 6, 20, 55, 75, 80, 89 

5,000 to 10,000 year precision ...................... 7, 17, 

39,90 

eastern tw~thirds of United States ..................... 7 

c 

Cap of the Anteroconid Complex ........... 10, 27, 34, 59 

configuration and significance .................... 58, 59 

CESAR core 14, Arctic Ocean •.•...••..••••.•••..•.•••.•..• 7, 88 

Chaline, Jean ............................................... 4, 6,10, 14 

classification ......•.............................................. 21 

concept of Allophaiomys .................................. 13 

concept of variability ........................................ 21 

enlarged Microtus .•.................•.•..••......•...... 15, 22 

projecting definitions ........................................ 53 

Chronophenetic ......................................................... 12 

Classification ............................................................. 21 

Climatic deterioration ................................................. 2 

Conclusion ................................................................ 89 

Continental 

deposition ............................................................ 2 

glaciation and eustatic sea level... ........... 2, 36, 55 

Conventions ................................................................ 7 

Correlation summary ................................................ 80 

Corriganville, Maryland .......................................•.... 42 

Cumberland, Maryland ............................................. 42 

INDEX 

D,E 

Dental characters: first lower molar 

basic triangles .................................................... 11 

capitalized .......................................................... 1 0 

dimensions ....................................... 1 0, 50, 58, 65 

dimension D-D' of van der Meulen ....•............... SO 

enamel-thickness differentiation ........... 1 0, 11, 14, 

25, 32, 41, 67, 84 

hypsodonty (dentine tracts, roots) .............•.....•.. 23 

of taxonomic significance .................................. 15 

posterior loop ..................................................... 11 

reentrants ............................................................ 11 

salient angles ............................................. , ........ II 

"typical" morphology ......................................... 11 

"typical" population ........................................... 11 

wings, primary ................................................... 1 0 

wings, secondary ................................................ 1 0 

Dental characters: last upper molar (M\3) ...........•.... 10 

Dispersal ............................................................... 73, 89 

450,000 years ago ...................... 44, 53, 56, 63, 77 

850,000 years ago ........................ 7, 39, 63, 71,87 

1.4Ma ............................................................... 60 

1.9Ma ........................................................... 7, 30 

constraints ........................................ 60, 77, 79,80 

Evolution 

anagenesis .................................................... 20, 23 

cladogenesis ......................... 17, 18, 19, 20, 53, 76 

gradual process .................................................. 23 

External age control .................................................. 39 

Extinction (by anagenesis) ................. 20, 31, 36, 80, 89 

F 

Fauna 

AllopluJiomys, oldest in North America ............. 30 

Aries, Kansas ........•.............................•.............. 43 

Balaruc, France ............................................ 29, 33 

Betfia-2 (Puspokfurdo), Romania ..................... 25, 

32,39, 70 

Cape Deceit, Alaska .................. 16, 47, 50, 54, 55, 

82,86,89 

Cheetah Room, West Vu-ginia ..... , .......... 38, 39, 43, 

51, 54, 56, 62, 64, 75, 76 

Courtland Canal, Kansas .................................... 43 

CKT-18, China .................................................... 6 

CRH-11, Yukon Territory .................................. 38 

CRH-47, Yukon Territory ..................... 38,44, 54, 

62, 79, 82, 86, 87 

CRH-64, Yukon Territory .................................. 38 

Cudahy, Kansas ............. 37, 41, 51, 59, 61, 63, 70, 

71, 77, 79,87 

Cumberland Cave, Maryland ......... .41, 42, 51, 52, 

55, 61, 63, 67, 68, 76,85 

Froman Ferry, Idaho .............................. 32, 60, 78 

Hanover Quarry fissure, Pennsylvania ............. .41, 

46, 51, 52, 64, 68, 72, 76, 86 

Hansen Bluff faunal sequence, Colorado .......... 34, 

61, 62, 65, 70, 72, 75,85 

Huangkan, China ................................................. 6 

Irvington, California .............................. 38, 60, 78 

Java, South Dakota ............................. 6, 38, 60,78 

Karay-Dubina, Ukraine ....................... ~7. 27, 30, 

48,58,84 

Kentuck, Kansas .......................................... 43, 70 

Fauna-Continued 

KL0--7 ............................................................. 82 

KL0--8 ....................................................... 82,83 

KL0-9 ....................................................... 82,84 

KLo..10 ........................................................... 82 

Krestovka, Yakutia (Olyor faunas) ............. 7, 55, 

58,82-84 

Kudun, Buryat ...•.•.....•....•... 6, 22, 27, 46,47, 48, 

55, 79, 84, 89 

Mas Rambault, France .................................... 33 

Monte Peglia, Italy .................................... 27,33 

Nash, Kansas ................................................... 43 

Porcupine Cave, Co1orado .............. 53,60,62, 72 

Razdolie, WestSiberia. ..........•... 17,19,53,66,67 

SAM Cave (BOf-4), New Mexico ............ 16,19, 

32, 33, 39, 46, 75, 77. 80, 85 

Sappa, Nebraska .............................................. 43 

Trout Cave No.2, West Vu-ginia ..................... 41 

Vallecito Creek, Anza-Borrego Desert, 

California ............•...................... 32, 50, 78 

Valerots, France ......................................... 33,47 

Villany-5, Hungary ..................................... 6,30 

Wathena, Kansas ........................................ 43,70 

Wellsch Valley, Saskatchewan ............ 36, 38, 51, 

54, 62, 79, 88 

Other North American faunas ........................ 43 

pinetorum species group ........................... 39, 65 

quasiater species group ...................... 34, 61,65 

G-K 

Generic or specific names (none introduced) .......... 25 

Genus 

Allophaiomys ................... 24, 25, 31, 33, 36, 38, 

41,42,43,47, 51, 53, 58, 60, 

62, 73, 79, 82, 89 

guildayi .......•. 34, 39, 41, 51, 52, 63, 68,76 

pliocaenicus ................ 25,34, 39,43,48, 53, 

58, 66, 70, 75, 84 

A., considered synonymous ............................. 28 

A., diagnosis ................................................... .25 

A., evolutionary extinction ............................... 31 

A., North American record .............................. 31 

A., oldest .......................................................... 30 

A., youngest ..................................................... 30 

Aratomys .......................................................... 24 

Arvicola ...............••..•.................•..........•..•.••.•. .24 

Atopomys ............•..................•........................ .24 

Chilotus ......................................••••................. 22 

Cromeromys ......................................... 22, 67,82 

Dicrostonyx .....•................•..••.•....•..........•... 55, 87 

renidens ....................................... 55,82,87 

simplicior ........•.•....•...........••............. .55, 87 

Eolagurus ..............••..................•..•............••.... 64 

Guildayomys ...•.•••.........•.•..••••.•.•.....•...•••...•...... 32 

Herpetomys .................................... 11, 46, 65, 74 

Hibbardomys •............•...••......•..........•....•........ .24 

lberomys .......................................................... 22 

Lagurus ................................................ 34,39,64 

Lasiopodomys ......... 4,11, 15,18, 22, 27, 28, 31, 

33, 36, 41, 44, 46, 50, 51, 52, 54, 

59, 61, 62, 65, 66, 70, 72, 73, 

75, 82, 84, 87, 89 

brandtii .................................... 28, 46,47,48 

97 
98 ALLOPHAIOMYS AND THE OLYOR SUITE, YAKUTIA 

Page 

Genus-Continued 

Lllsiopodomys--Continued 

deceitensis .................... 6, 15, 18, 38, 42, 4 7, 

50, 53, 55, 61, 65, 76, 84,89 

mandarinus .................................... 28, 48, 52 

praebrandtii ...................... .47, 48, 79, 80, 89 

probrandtii ................................................. 48 

ratticepoides ................................. 5, 6, 47, 50 

?1Asiopodomys .......•.............................. .41, 52, 76 

Lemmiscus ............... 16, 18, 21, 22, 31, 33, 39, 44, 

48, 51, 61, 64, 73, 75,85 

Meridiopitymys .................................................. 10 

Microtus ............. .4, 22, 23, 25, 30, 31, 33, 36, 37, 

44, 50, 52, 54, 56, 58, 60, 61, 

63, 67, 70, 73, 75, 79, 84 

califomicus .......................................... 64, 97 

montanus .................................................... 33 

nivalis ....................................... 41, 48, 58, 86 

ex gr. oeconomus ........................ 5, 27, 84, 94 

oregonensis .......................................... 56, 79 

paroperarius ........... 6, 10, 15, 18, 20, 34, 37, 

42,47, 50, 52, 53, 56, 58, 59, 61, 

62, 70, 71, 75, 77, 79, 80 

xanthognathus ...................................... 11, 44 

Micrurus ....................................................... 10, 66 

Mictomys .................. 32, 38, 42, 52, 60, 65, 75, 78 

Mimomys ............ 21, 24, 32, 38, 53, 60, 67, 78,82 

Nebraskomys ...................................................... 24 

Neodon ................................................... 28, 65, 74 

Ondatra .................................................. 32, 60, 78 

Orithriomys ...................................... 11, 46, 65, 74 

Pedomys .................. 11, 13, 17, 18, 23, 30, 36, 41, 

52, 53, 62, 63, 65, 73, 80 

llanensis ........... 11, 18,32,41,43,63, 70,76 

ochrogaster .............................. 19, 31, 41,68 

Phaiomys ............ 13,18, 21, 22, 24, 28, 31, 34,65 

Phaiomys: in Moscow collections ...................... 29 

Phenacomys ............. 24, 32, 38, 54, 60, 64, 75, 89 

Pitymys ................ 1, 10, 14,17,18,19,22,27,29, 

32, 34, 36, 38, 51, 53, 59, 

61, 67, 70, 73, 80 

cumberlandensis ............... 10, 14, 39, 51, 54, 

62, 63, 67, 70,76 

pinetorum ..................... 14, 39,41, 43, 64, 67, 

71, 76,80 

morpho types ........................................ 18, 32 

(=Old World Terricola) ........................ 1, 10, 

22, 27, 44, 66, 67 

Pliophenacomys ................................................. 32 

Polonomys .......................................................... 24 

Proedromys ........................................................ 24 

Prolagurus .......................................................... 67 

Promimomys ....................................................... 24 

Prosomys ............................................................ 24 

Stenocranius ................................................. 22, 44 

Suranomys .......................................................... 22 

Synaptomys ....................................................... 21 

Terricola .................... 1,10, 13, 15,17, 22, 25, 30, 

33, 36, 44, 50, 54, 55, 58, 

59, 65, 66, 71, 73, 77 

hintoni ............................................ 31,44, 66 

meadensis ............... l5, 59, 61, 71, 75, 78,81 

quasiater .............................................. 34, 71 

savii ...................................................... 66, 70 

subterraneus ......................................... 66, 70 

tatricus ....................................................... 61 

Tyrrhenicola ....................................................... 65 

''Villanyia " .......................................................... 24 

Geologic time terms 

early-middle Pleistocene boundary ...................... 9 

'!!rU.S. GOVERNMENT PRINTING OFFICE: 1993-774-049/66039 

Page 

Geologic time terms-Continued 

Pliocene-Pleistocene boundary ......................... 10 

middle-late Pliocene boundary .......................... 10 

microtine ages ................................................... 10 

Hinton (definitions: Pitymys, Microtus) ...........•. 23, 44, 

59,65 

Kolyma Lowlands ...................................... 2, 21, 82, 87 

Kolyma River ............................................................... 2 

Krestovka River ........................................................... 2 

Krestovka Sections ................. 3, 15, 21, 37, 55, 58, 63, 

64, 75, 82, 87 

Begunov Suite (Pliocene) .................................... 2 

Kutuyakh Beds (Pliocene) ............................. 2, 82 

Olyor Suite (Pliocene and Pleistocene) .............. 2, 

15, 21, 24, 48, 55, 58, 60, 

63, 64, 75, 79, 82 

stratigraphic units ............................................ 2, 7 

M-0 

Mammalian ages (Europe) 

Biharian Stage ........................... 30, 47, 48, 55, 82 

Villanyian .......................................................... 30 

Mammalian ages (United States) 

Blancan mammal age ................ 30, 32, 37, 60,78 

Irvingtonian mammal age ............... 10, 30, 32, 39, 

56, 75,78 

Rancholabrean mammal age ....................... 10, 56 

Microtine faunas, age significance ............ 7,17, 39,90 

Microtini, Tribe ............. 4, 7, 20, 23, 25, 33, 44, 48, 92 

Morphotypes 

listed as species .............. 6, 11, 14,16, 17, 23, 30, 

31, 37, 48, 51, 53, 58, 61, 66, 70, 75, 84 

Mosaic evolution .......................................... 20, 48, 75 

Allophaiomys ............................................... 15, 25 

Multiple origins ............................. 6, 13, 18, 20, 67,73 

biochronologic significance ............................... 20 

genera ................................................................ 13 

microtine tribes .................................................. 13 

New Mexico, U.S.A. .................. 16, 24, 33, 36, 46, 61, 

64, 73, 75, 80 

Nomenclature, rules of ................................ 8, 9, 16, 23 

authority of type .......................................... 23, 24 

Nomina vana .............................................................. 11 

North Atlantic Ocean ................................................. 33 

Old Crow (basin and river), Yukon Territory ........... 38, 

54, 62, 72, 79, 82, 86, 87 

Oldest permafrost .................................................. 2, 89 

Olyor Suite .................. 2, 15, 21, 24, 48, 55, 58, 60, 63, 

64, 75, 79, 82 

different opinions, age ..................................... 4, 5 

polarity reversal ........................ 2, 3, 4, 5, 7, 9, 82, 

86, 87,88 

type section .............................................. 2, 87, 89 

unconformably separated from Kutuyakh 

Beds ............................................................. 2 

Oriental faunal region ....................... 19, 22, 29, 46, 47, 

48, 50,56 

p 

Paleomagnetic events 

boundaries ..................................................... 9, 10 

Brunhes Normal-polarity Chron ............. 2, 4, 5, 6, 

7, 9, 18, 30, 31, 33, 36, 38, 50, 54, 55, 56, 

59, 63, 67, 72, 75, 77, 79, 82, 87 

Cobb Mountain Normal-polarity Subchron ..... 2, 7, 

51,88 

Gauss Normal-polarity Chron ............... 2, 10, 30, 

31,61 

Jaramillo Normal-polarity Subchron .......... 2, 4, 6, 

7, 30, 33, 36, 38, 50, 55, 59, 61, 63, 

65, 67, 71, 75, 77, 79, 87,88 

Page 

Paleomagnetic events-Continued 

Matuyama Reversed-polarity Cbron ............... 2, 7, 

10, 30, 33, 36, 46, 50, 54, 61, 67, 88 

Olduvai Normal-polarity Subchron .............. 6, 10, 

22, 27, 30, 32, 33, 36, 38, 46, 48, 50, 

55, 59, 62, 78, 84, 86, 88 

Pitymyini, Tribe .................. 4, 7, 20, 23, 25, 27, 28, 32, 

34, 36, 41, 44, 55, 59, 61, 65, 67, 71,73 

"Pitymys rhomboid" or "Pitymyan rhombus" ........... 23 

Polarize: morphotypes ................ 13, 14, 17, 20, 22, 41, 

44, 58, 61, 66, 76,79 

Population characteristics .................. 5, 6, 7, 10-25,27, 

28, 30, 34, 36, 47, 50, 51, 52, 53, 

63,66,68,71, 75-80,84,86 

Provincial history: required in correlation .......... 20, 21, 

31, 39, 47, 56, 60,74-80, 84, 89,91 

Anza-Borrego Desert faunas ............................. 78 

Cheetah Room fauna ......................................... 75 

Chinese faunal region ................................. .47, 79 

Cumberland Cave fauna .................................... 62 

~ocky Mountain barrier ..................................... 80 

SAM Cave fauna ................................................ 75 

Trout Cave No. 2 fauna ...................................... 77 

Proxy characterization ............................................... 17 

Pitymys hibbardi ................................................ 17 

Pedomys llanensis ........................................ 11, 41 

R,S 

Random character states ............................................ 14 

Rio Grande ................................... 33, 36, 61, 62, 65,75 

Rocky Mountains .................... 7, 19, 21, 31, 32, 36, 37, 

38, 51, 53, 55, 56, 60, 62, 63, 64, 

71, 72, 73, 78, 79, 80, 87,91 

Rootless cheek teeth ................................ 21, 23, 25,30 

Saskatchewan ............. 36, 38, 44, 51, 54, 56, 62, 63, 79 

Sher, A.V .............................................. 2, 4, 5, 7, 59,88 

Site 644, Norwegian Sea ...............•........................•... 88 

Stage of evolution ........ 7, 12, 15, 21, 23, 31, 32, 73, 87 

Stratophenetic ............................................................ 12 

Suite (Soviet usage) ..................................................... 2 

Systematic boundary ................... 15, 17, 18, 52, 53, 86 

T-Z 

Taxon 

defined by population limits .............................. 24 

derived: hyphenated name ................................. 24 

Taxonomy ........................................................ 7, 13,24 

purpose ........................................................ 53, 89 

Temporal sequencing, methods .................................. 12 

Tesakov, Alexy ....................................................... 4, 34 

Tune scales ................................................................... 9 

Tune transgressive: Microtus replacing 

Allophaiomys ........................................................... 6 

1Ype population ................ 5,11,15, 17, 23, 25, 28, 29, 

32, 39, 48, 52, 61, 70,77 

1Ype sample ............................. 5, 11, 23, 27, 41, 61, 64 

Type species: concept ............ 5, 11, 25, 28, 39, 44, 46, 

56, 64, 65, 67. 68, 71 

"Typical" ............................................ 11, 25, 46, 48, 56 

Uniform classification: limits .............. 7, 21, 24, 67, 89 

Variability ......................... 5, 11-20, 22, 23, 25, 28, 31, 

41, 43, 48, 52, 58, 59 

Vernacular nomenclature: history, present 

usage ....................................................................... 8 

Yakutia (Yakut A.S.S.R.) ....................... 2, 7, 21, 58,82 

Yukon Territory, Canada ..................... 2, 38, 44, 54, 55, 

60,62,64,72 

Zazhigin, V.S ................................. .4, 5, 6, 7, 46, 58, 89 


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