The 8eri ngian Ancestry of 

Phenacomys (Rodentia: Cricetidae) 

and the Beginning of the Modern 

Arctic Ocean, Borderland Biota 

U.S. GEOLOGICAL SURVEY BULLETIN 1687 

The Beringian Ancestry of 

Phenacomys (Rodentia: Cricetidae) 

and the Beginning of the Modern 

Arctic Ocean Borderland Biota 

By CHARLES A. REPENNING, ELISABETH M. BROUWERS, 

L. DAVID CARTER, LOUIE MARINCOVICH, JR., and 

THOMAS A. AGER 

Pliocene fossils from Fish Creek, Alaska, 

indicate a correlation of the oldest 

lowland tundra and cooling of the 

Arctic Ocean borderland with the 

oldest Northern Hemisphere glaciation 

U.S. GEOLOGICAL SURVEY BULLETIN 1687 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1987 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging in Publicati«)n Data 

The Beringian ancestry of Phenacomys (Rodentia, Cricetidae) and the beginning of the modern Arctic Ocean borderland biota. 

(U.S. Geological Survey bulletin ; 1687) 

"Pliocene fossils from Fish Creek, Alaska, indicate a correlation of the oldest lowland tundra and cooling of the Arctic Ocean borderland with the 

oldest Northern Hemisphere glaciation." 

Bibliography: p. 

Supt. of Docs. no.: 119.3:1687 

1. Phenacomys, Fossil. 2. Paleontology-Pliocene. 3. Paleontology-Alaska-Fish Creek Watershed. 4. Paleontology-Arctic regions. 

5. Paleoclimatology-Arctic regions. I. Repenning, Charles Albert, 1922-

11. Series. 

QE75.B9 no. 1687 

[QE882.R6] 

557.3 s 

[569' .323] 

86-600255 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgments 2 

Mammals of the Fish Creek Fauna 3 

Genus Phenacomys Merriam 4 

Phenacomys gryci Repenning, n. sp. 6 

Genus Cromeromys Zazhigin 7 

Ostracodes of the Fish Creek section 11 

Basal assemblage 11 

Upper assemblage-the Fish Creek Fauna 14 

Mollusks of the Fish Creek Fauna 14 

Flora of the Fish Creek section 18 

Correlation in the Arctic Ocean Borderland 20 

Age of the Fish Creek Fauna 20 

Age of the Ocean Point Fauna 24 

Age of the Cape Deceit Fauna 24 

Age of the Krestovka Section 25 

Age of the Kap Kobenhavn Fauna 25 

Environment of the Arctic Ocean Borderland between 3.0 and 1.9 Ma 26 

References cited 27 

Index 29 

PLATE 

[Plate follows index] 

1. Scanning electron micrographs of diagnostic ostracode species from Fish 

Creek section. 

FIGURES 

1. Map showing locations in northern Alaska mentioned in text 2 

2. Map showing Beringia, including localities of pre-Pleistocene microtine 

faunas 3 

3. Stratigraphic section of marine and marginal marine sediments of Gubik 

Formation at Fish Creek, northern Alaska 5 

4-7. Sketches showing: 

4. First lower left molars of species of Synaptomys (Plioctomys) 6 

5. First lower molars of Phenacomys deeringensis from Cape Deceit 

Fauna 7 

6. First lower molars of Phenacomys gryci from Fish Creek Fauna 8 

7. Cheek teeth of Cromeromys and Phenacomys 9 

8. Plot of ostracode abundance and species diversity, Fish Creek section 10 

9. Map showing localities and zoogeographic distribution of Pterygocythereis 

n.sp. and Rabilimis species used for this study 12 

10. Diagram showing stratigraphic range of the three Rabilimis species in 

Pacific, North Atlantic, and Arctic Oceans 14 

11. Sketches and scanning electron micrographs of Rabilimis and 

Echinocythereis 16 

Contents Ill 
IV Contents 

12. Map showing zoogeographic distribution of Echinocythereis and 

Pterygocythereis species in this study 18 

13. Chart correlating faunas from Beringian Siberia and Alaska with time, 

paleomagnetic stratigraphy, and oxygen isotope ratios 22 

14. Sketch outlining evolutionary history of brown and bog lemmings, Subfamily Lemminae 23 

TABLES 

1. Ostracode species present at Fish Creek 15 

2. Origins of Fish Creek mollusks 17 

3. Pollen and spore counts of four samples from Fish Creek 21 
The Beri ngian Ancestry of Phenacomys 

(Rodentia: Cricetidae) and the Beginning 

of the Modern Arctic Ocean Borderland Biota· 

By Charles A. Repenning, Elisabeth M. Brouwers, L. David Carter, 

Louie Marincovich, Jr., and Thomas A. Ager 

Abstract 

The living North American heather vole, genus 

Phenacomys, is one of the few living microtine rodent genera 

whose ancestry has not been traced back to the Miocene. A 

recently discovered fossil Phenacomys from the late Pliocene 

part of the Gubik Formation along Fish Creek, northern Alaska, 

clearly resembles the extinct Asiatic genus Cromeromys, a progressive offshoot of the extinct Hoi arctic genus Mimomys, suggesting the probable ancestry. 

Marine ostracodes from the base of the Fish Creek section record a much warmer Arctic Ocean than do those found 

high in the section with the fossil Phenacomys. Both mollusks 

and mammals in the fauna with Phenacomys indicate that this 

ocean was not perennially frozen during deposition of the upper part of the section. Pollen in the Fish Creek section records 

a transition from shrub tundra with nearby conifer forests in 

the lower part to herbaceous tundra with the mollusks and 

mammals of the Fish Creek Fauna. 

Correlation, by means of rodent evolution and magnetic 

patterns, with a similar floral transition in northeastern Siberia 

and with the oxygen isotope record of the northern oceans indicates that the floral change probably represents the first 

development of widespread, low-elevation tundra in the Arctic 

Ocean Borderland and indicates an age of 2.4 Ma for the Fish 

Creek Fauna in the upper part of the section. 

The Fish Creek Fauna lived during the time span that includes the beginning of the first significant accumulation of continental ice in the Northern Hemisphere, according to oceanic 

and North American terrestrial records. The older parts of the 

Fish Creek section record part of the climatic deterioration that 

led to this first glaciation. This climatic history integrates the 

known late Pliocene history of climatic change in the Arctic 

Ocean and its borderland. 

INTRODUCTION 

Fish Creek drains into the Arctic Ocean at Harrison 

Bay to the west side of the Colville River delta. The fossil 

locality of this report is about 15 miles (24 km) 1 south 

1

Distances are given in miles (the common United States unit), but 

conversion to kilometers is given to accord with metric measurements 

of the report. 

of the Arctic Ocean at lat 70°16' N., long 152001' W. 

It is the most northerly pre-Pleistocene microtine rodent 

fauna known (figs. 1, 2) and one of very few Tertiary 

mammalian faunas from Beringia, that part of northeastern Siberia and northwestern North America on either 

side of the Bering Strait that shares great faunal and floral 

similarity. 

The Gubik Formation exposed at the Fish Creek 

locality is of Pliocene age and consists of 10-12 m of 

marine and estuarine sediments that have been described as consisting of two units (Carter and others, 1986): 

a basal unit about 4 m thick composed of distinctly to 

indistinctly bedded dark-gray silt containing scattered 

granules of chert and quartz, sparse sand interbeds with 

sand-filled burrows, and a few mollusk shells; and an upper unit composed of fossiliferous brown to gray sand, 

pebbly sand, and silt that is predominantly trough crossbedded but includes evenly bedded zones that are relatively thin and discontinuous. 

The character of the cross-strata in the upper unit 

was interpreted by Carter and Galloway (1985) to indicate 

deposition in a tidal channel. A strong dominant current 

is indicated by sets of large-scale cross-strata as thick as 

4 m, which have consistent foreset dips to the northnortheast. A nearly opposed subordinant current is indicated by ripple stratification that has built up the dip 

of the large-scale foreset beds, and by sets of mediumscale cross-strata that contain molluscan and mammalian 

fossils of the Fish Creek Fauna. 

Lithologic changes for the part of the exposure 

where most of the samples discussed here were collected 

are shown in figure 3, in which the median gray sand unit 

and the upper silt represent the tidal channel deposits of 

Carter and Galloway (1985). These marine deposits are 

overlain by alluvial and eolian sands. One sample from 

the lowest part of the section is normally magnetized; 

the remainder of the section is reversely magnetized 

(V. Pease, written commun., 1985; Carter and others, 

1986). 

A few ostracodes markedly different from those in 

the upper part of the 5-m medial gray sand unit occur 

at the base of the lower silt and clay unit. These ostracodes 

Introduction 1 
Point Barrow 

BEAUFORT SEA 

CHUKCHI SEA 

Figure 1. Location of places and features in northern Alaska mentioned in the text. Dashed line, general physiographic boundary. Anticline symbol shows strike, dip, and plunge. 

are excluded from the formal Fish Creek Fauna because 

they are thought to be substantially older. Ostracodes of 

the Fish Creek Fauna are abundant and diverse 1.5 m 

above the base of the medial sand unit and in two molluskrich beds at the top of this unit. Mollusks occur throughout the section, but are most abundant only in a distinct, 

organic-rich shell bed in the upper 1.5 m of the medial 

sand unit. Palynomorphs occur 3 m above the base of the 

section and with the ostracodes of the upper part of the 

medial sand unit, about 7.5 m above the base of the exposures. These are the only samples of pollen not flooded with reworked Cretaceous pollen and that are believed 

to reflect the vegetation at the time of deposition. Large, 

shallow-water benthic foraminifers (Elphidiella groenlandica and Cyclogyra involvens, fide K. McDougall, oral 

commun., 1984) are common in the upper part of the 

medial sand unit; fossil bone, primarily microtine rodent 

remains, is common in the mollusk-bearing bed of the 

medial sand unit, about 9 m above the base of the 

exposure. 

The exposures along Fish Creek have been discussed 

by Carter and others (1979), who proposed a middle 

Pleistocene age based on very limited data. Carter and 

Galloway (1985) preferred a late Pliocene age based partially on data reported more fully herein. The locality is 

the type section of the Fishcreekian transgression as used 

by Brouwers and others (1984) and dated as 1.2 Ma, and 

as named by Carter and Brigham-Grette (in press). 

Microtine rodent teeth were first discovered in 1983 

in washed mollusk samples, along with small waterrounded fragments of other mammals. The microtine 

teeth are generally not abraded, and many are perfectly 

2 Ancestry of Phenacomys and Arctic Borderland Biota 

preserved, with no rounding of their delicate features. One 

last upper molar of a microtine bears a fragment of its 

maxillary still adhering to one side of the roots, a situation hardly plausible if the fossils had been reworked from 

older unconsolidated deposits. The microtine teeth represent two species, a primitive lemming and a new and 

primitive species of the heather vole Phenacomys. Further collecting at Fish Creek in 1984 yielded only a few 

additional teeth. 

All mammalian specimen numbers from the Fish 

Creek Fauna are from the catalog of the National 

Museum of Natural History, Smithsonian Institution, and 

are prefixed by the abbreviation USNM. University of 

Alaska specimens from the Cape Deceit Fauna of the 

Seward Peninsula (fig. 2), described by Guthrie and Matthews (1972), are prefixed by the abbreviation UA. 

Acknowledgments 

Charles L. Powell (USGS, Menlo Park) first found 

fossil bone and teeth while picking fossil mollusks from 

samples collected at Fish Creek, reflecting an interdisciplinary interest not often found in paleontology. 

Mary L. McGann, Ginger Vagenas, and Katherine B. Lormand (USGS, Menlo Park) spent long weeks in further 

picking of the samples for microtine teeth. Katherine M. 

Reed (Geological Survey of Washington, Seattle) and John 

Galloway (USGS, Menlo Park) returned to the Fish Creek 

locality with Carter in 1984 and screened for additional 

rodent teeth. Joseph E. Hazel, Leo Laporte, and J. Platt 

Bradbury reviewed earlier versions of the manuscript and 

offered helpful suggestions. 
BERING SEA Island 

PACIFIC OCEAN 

500 MILES 

I 

500 KILOMETERS 

Figure 2. Beringia, showing places mentioned in text, including the pre-Pleistocene microtine faunas discussed: Krestovka Section in Yakutsk, northeastern Siberia; Cape Deceit Fauna of Seward Peninsula, Alaska; Fish Creek Fauna of the North Slope, 

Alaska; and faunas of Old Crow Basin of Yukon Territory, Canada. Old Crow Basin contains microtine rodents of Pliocene age, 

but age relationships are unknown and localities are not further discussed. 

MAMMALS OF THE FISH CREEK FAUNA 

Nearly all identifiable mammalian fossils are from 

a 5.0- to 7 .6-cm-thick interval within the most conspicuous mollusk-bearing bed, which is 15-23 em below 

the upper contact of the medial gray sand. This part of 

the Fish Creek section is shown (fig. 3) above the largescale cross bedded deposits that are believed to be of tidalchannel origin, but it is actually interbedded with them 

along strike, and the entire unit is composed of lenses 

and lenticular beds of the two lithologies. The mammalbearing deposits are characterized by medium-scale 

crossbedding. Organic detritus is common in these parts 

of the cross-stratified medial gray sand, particularly in 

the mollusk-rich zones, and includes fragments of wood, 

one specimen of which has been identified as Larix (larch) 

(Carter and Galloway, 1985). Larch does not now grow 

north of the Brooks Range. The fauna consists of two 

microtines, miscellaneous fish remains, a few bird bones, 

the lower third premolar of the pika Ochotona sp. cf. 

0. alpina, two incomplete teeth of a ground squirrel that 

could be Spermophilus undulatus, and a single well-worn 

and abraded lower fourth premolar that resembles that 

of the "crab-eating" otter Enhydriodon. 

The Enhydriodon lower fourth premolar (USNM 

264293) has a root development comparable to that indicated by the alveolae of this tooth in a fossil edentulous 

ramus of a sea otter (USNM 264275) found in a marginalmarine unit of the Gubik Formation at Ocean Point (fig. 

1), about 16 miles (25 km) to the southeast of the Fish 

Creek locality (Repenning, 1983a). The tooth from Fish 

Creek does not resemble that of the living sea otter, 

Enhydra lutris, and is more Enhydriodon-like, and less 

Enhydra-like, than Enhydriodon? reevei from the Norwich Crag in East Anglia (see discussion in Repenning, 

1983a). The Norwich Crag also contains a microtine rodent fauna that is Villangian in age, between 1.9 and 2.6 

Ma old. The youngest known unquestioned Enhydriodon 

from North America is approximately 3 Ma old (Repenning, 1976). The decision as to whether these specimens 

from the Arctic Ocean Borderland should be considered 

the earliest known and most primitive Enhydra or a late 

record of Enhydriodon awaits discovery of additional 

material. However, the two records of an intermediate 

form in marginal-marine Pliocene deposits of the Arctic 

Ocean, at Ocean Point and at Fish Creek, suggest that 

evolution of the North Pacific sea otter may have taken 

place in the Arctic Ocean. Further, the records enhance 

Mammals of the Fish Creek Fauna 3 
the possibility of a relationship of the living sea otter to 

Enhydriodon? reevei (Newton) from the English Norwich 

Crag, a possibility considered less likely in earlier publications by Repenning (1976, 1983a). 

The two microtine rodent species from the Fish 

Creek locality are represented by 19 teeth (including 9 first 

lower molars and 2last upper molars) of the new species 

of heather vole described herein and 3 teeth (including 

one incomplete first lower molar) of the bog lemming 

identified as Synaptomys (Plioctomys) mimomiformis 

Suchov. 

The first lower molar of the bog lemming is shown 

in figure 4; the resemblance is strong to that of the 4.5 

to 4.0 Ma old S. (P.) mimomiformis Suchov (1976) from 

the western side of the southern Ural Mountains north 

of the Caspian Sea, and to that of the 3. 7 to 2.6 Ma old 

S. (P.) europaeus Kowalski (1977), from southern 

Poland, which appears to be a subgeneric and probably 

specific synonym of S. (P.) mimomiformis (von 

Koenigswald and Martin, 1984). Zazhigin (in Sher, 

Virina, and Zazhigin, 1977, and also in Sher and others, 

1979) reported Synaptomys (cf. Plioctomys) sp. from the 

Kutuyakh Beds in the Krestovka Section of the Kolyma 

Lowlands (fig. 2). The Kutuyakh Beds are between 3.4 

and 2.4 Ma old (Repenning, 1984). The resemblance of 

the Fish Creek lemming is less close to Synaptomys (Plioctomys) rinkeri Hibbard from Blancan V faunas of the 

Great Plains of North America (between 2.6 and 1.9 Ma 

old) because the anterobuccal reentrant of the first lower 

molar, which is on the anteroconid complex of this tooth, 

is much less developed. £margination of this reentrant 

increases in younger forms to the extreme condition 

found in living Synaptomys (Synaptomys) cooperi Baird. 

Von Koenigswald and Martin (1984) reported that the 

primitive ''Schmelzmuster,'' or enamel structure, persists 

in Synaptomys at least to the S. rinkeri stage. Synaptomys 

now lives only in North America. 

Genus Phenacomys Merriam 

Type Species.-Phenacomys intermedius Merriam, 

the heather vole of North America. 

Range.-Now living in Canada and in the Canadian and Hudsonian life zones of the United States and 

known as a fossil in faunas of northeastern Siberia and 

northwestern North America that are herein recognized 

to be as old as 2.5 Ma. Phenacomys is not known in the 

conterminous United States until approximately 800,000 

years ago and apparently was more or less confined to 

Beringia, the areas of Asia and North America near Bering Strait (fig. 2), prior to that time. However, recent 

evidence from Walter W. Dalquest (written commun., 

1985) suggests, indirectly, that some undated fossil 

records in the United States may be twice that old. The 

4 Ancestry of Phenacomys and Arctic Borderland Biota 

lack of a similar southward dispersal in Asia possibly is 

related to the much less extensive development of continental ice in Eurasia 800,000 years ago (Repenning, 

1984). 

Diagnosis.-Phenacomys is an arvicoline microtine 

rodent2 with rooted, hypsodont cheek teeth having no 

cementum deposited in the reentrant angles; the commissures of the posterior loop and three basic triangles 

of the first lower molar (Repenning, 1983c) have a strong 

tendency toward a position buccal to the sagittal midline 

of this tooth; the anteroconid complex of the first lower 

molar has from two poorly pinched-off accessory 

triangles to four well-separated accessory triangles, varying with wear and with stage of evolution; the variability 

in configuration of the cap of the anteroconid complex 

is remarkably great with both wear and stage of evolution; the anteroconid complex never contains an enamel 

islet, although a "Mimomys Kante" is present in older 

forms; dentine tracts increase in height with evolution; 

and the last upper molar has two buccal and two lingual 

well-formed reentrants in all stages of evolution with no 

islet preserved in the posterior loop. 

Discussion.-Johnson (1973) has suggested that the 

living Phenacomys longicaudus is sufficiently distinct 

from Phenacomys intermedius to warrant designation as 

Arborimys longicaudus. This question has not been further considered in the present study, and the three living 

species, P. intermedius, P. longicaudus, and P. albipes 

(also included in Arborimys by Maser and others, 1981 ), 

are retained in Phenacomys without opinion. 

Only two pre-Pleistocene records of Phenacomys 

have been published, one in Alaska and one in Siberia. 

The Siberian fossil has been compared with the Alaskan 

extinct species Phenacomys deeringensis (Guthrie and 

Matthews, 1971) and this form of Phenacomys is considered to be more primitive; very low dentine tracts were 

noted (Sher, Gitterman, and others, 1977). Phenacomys 

deerjngensis from the Cape Deceit Fauna of the Seward 

Peninsula, Alaska, was described as Pliomys, but Chaline 

( 197 5) placed it in Phenacomys because of the characters 

of the first lower molar and the non-Pliomys enamel pattern of the last upper molar. The great variation, with 

wear, of the configuration of the enamel pattern on the 

anteroconid complex is particularly vexing in the identification of Phenacomys deeringensis (fig. 5); this is a 

character of the generic lineage, but is especially evident 

in more primitive species. 

Phenacomys deeringensis is the only previously 

2What are commonly called microtine, or arvicoline, rodents of 

the Subfamily Arvicolinae have five separate origins in the low-crowned 

cricetid rodents and the subfamily is polyphyletic. The Subfamily Arvicolinae is here restricted to those microtines (a descriptive term) that 

derive from the genus Mimomys. 
named extinct species of the genus. 3 At any stage in 

tooth wear, the variations of the enamel pattern on the 

occlusal surface of the first lower molar of Phenacomys 

deeringensis are essentially identical to variations found 

in specimens of living Phenacomys intermedius. 

However, similar patterns appear in earlier stages of wear 

in P. deeringensis because the reentrant angles on the 

anteroconid complex responsible for these variations in 

enamel pattern persist relatively shorter distances down 

the sides of the tooth and thus are lost with relatively less 

wear. The root-ward extent of these reentrants also varies 

individually. Dentine tract development and the basic 

structure of the last upper molar are essentially the same 

in the two species. Phenacomys deeringensis is large, 

however, and the length of the first lower molar4 

averages about 3 mm compared to about 2.5 mm in P. 

intermedius. 

The Cape Deceit Fauna (fig. 2), from which 

Phenacomys deeringensis was described, also is the type 

fauna of the most primitive known collared lemming, 

Predicrostonyx hopkinsi, and of a very primitive form of 

the Microtus lineage which seems best assigned to 

Lasiopodomys deceitensis (Guthrie and Matthews) (see 

fig. 2e in Repenning, 1983c). This member of the Microtus 

lineage is not greatly modernized from Lasiopodomys 

prebraebranti Erbaeva (1976) (sometimes assigned to 

Allophaiomys, the ancestral genus) from central Siberia 

(see Repenning, 1983b ). The oldest record of the Microtus 

lineage in the Krestovka Section of northeast Siberia, also 

described as archaic (Sher and others, 1979) and close to 

the ''Arvicola-Allophaiomys group" (Vangengeim and 

Sher, 1970), is immediately below the Reunion Subchron 

(about 2.1 Ma according to a recent reevaluation of the 

data) (Repenning, 1984). The lineage is clearly of Asian 

origin and there is no basis for assuming an older age at 

Cape Deceit. As both Cape Deceit and the Krestovka Section are in the Beringian Faunal Province and share many 

faunal similarities, it is possible that the Cape Deceit 

Fauna and the first appearance of Microtus in the 

Krestovka Section are coeval. Microtus first appeared in 

temperate North America and Europe about 200,000 years 

later than the first appearance in the Arctic. 

Thndra flora is indicated by pollen and insects from 

the deposits containing the Cape Deceit Fauna, which 

overlie strata whose pollen indicates a regional tree line 

very near to the locality (Matthews, 1974). The deposits 

underlying the Cape Deceit Fauna contain evidence of 

3 As has been noted by others including Chaline (1975), the extinct North American Pliocene genus Pliophenacomys is unrelated to 

the Phenacomys lineage and is not an arvicoline microtine; that is, it 

does not derive from the genus Mimomys. 4

Guthrie and Matthews (1972) indicated a size range of about 

3.3-4.7 mm, but there appears to have been a 1-mm error in lettering 

of their figure 8. Presently available specimens (four first lower molars) 

show a range between 2.7 and 3.1 mm. 

alternating tundra and forest or forest-tundra. The tundra in which the Cape Deceit Fauna lived is believed to 

have been influenced by local permafrost and to represent a climate colder than at present (Matthews, 197 4, 

table 6-Cape Deceit Formation, Unit 2). 

The above-mentioned microtine rodents indicate a 

Blancan V age for the Cape Deceit Fauna, between 2.0 

METERS 

Fish Creek Fauna 

Upper ostracode 

assemblage 

Lower ostracode 

assemblage 

10 -r-=....._..i83EB186 

9 

8 

7 

6 

83EB178 

5 

78ACr60b 

4 

3 

2 

3EB173 

1-

z 

:::> 

c 

z 

<( 

(/) 

>- <( 

a: 

(!) 

...J 

<( 

c 

w 

:1! 

t:: 

z 

:::> 

~ 

u; 

a: 

w 

~ 

g 

Main mammal fauna 

Mollusk fauna 

Youngest pollen flora 

Some mammals 

Pollen flora 

Pollen flora 

Oldest pollen flora 

Very few mollusks 

(unidentifiable) 

Figure 3. Stratigraphic section of marine and marginal marine 

sediments of the Gubik Formation at Fish Creek, showing 

stratigraphic position of microfossil samples, Fish Creek Fauna, 

and ostracode assemblages. EB, samples collected by Elisabeth 

Brouwers; ACr, samples collected by L. David Carter. 

Mammals of the Fish Creek Fauna 5 
0 2 mm 

A 8 c D 

Figure 4. First lower left molars of species of Synaptomys (Piioctomys). Note differences in development of the left upper 

(anterobuccal) syncline or reentrant; size is variable although 5. (P.) rinkeri averages largest. A, Molar of 5. (Piioctomys) mimomiformis Suchov from the Simbugino Fauna near Ufa, Bashkir A.S.S.R., Moldavian mammal age, between 4.5 and 4.0 Ma. Redrawn 

from Suchov (1976). B, Molar of 5. (P.) europaeus Kowalski from the Rebielice Krolewskie I Fauna, Poland, Rebielice mammal 

age, between 3.7 and 2.6 Ma. Redrawn from Kowalski (1977). C, Molar of 5ynaptomys (Piioctomys) mimomiformis from the 

Fish Creek Fauna near Point Barrow, Alaska (USNM 264294). 0, Molar of 5. (P/ioctomys) rinkeri Hibbard from the White Rock 

Fauna near Republic, Kansas, Blancan V mammal age, between 2.6 and 1.9 Ma. Redrawn from Eshelman (1975). 

and 2.6 Ma old. None of these microtines are known in 

Holarctica before this time, and by the end of Blancan 

V time fully developed Microtus species lived both in 

temperate North America and in Europe, and 

Predicrostonyx had evolved into the modern genus 

Dicrostonyx in the Old World. Given these time constraints, the presence of Lasiopodomys deceitensis is compelling evidence for inferring an age no older than 2.1 

Ma (age of first Microtus in the Krestovka Section) for 

the Cape Deceit Fauna. The primitive collared lemming 

makes it difficult to assign a younger age to the Cape 

Deceit Fauna. The climatic history of Holarctica is in 

complete agreement with this interpretation (Repenning, 

1984), and it seems most probable that the Cape Deceit 

Fauna is about 2.1 Ma old, although paleomagnetic support is not available. 

Zazhigin (in Sher, Gitterman, and others, 1977) has 

reported Phenacomys sp. from the Krestovka River 4 km 

upstream from the main exposure (fig. 2). This occurrence is not assignable with certainty to the Kutuyakh 

Beds of the Kolyma Lowlands (Zazhigin in Sher and 

others, 1979), which are between 3.4 and 2.4 Ma old. This 

Siberian record has not been described or illustrated, 

6 Ancestry of Phenacomys and Arctic Borderland Biota 

although Zazhigin noted that it was smaller than P. deeringensis and had very low dentine tracts. The new species 

of Phenacomys here described is markedly more primitive 

than Phenacomys deeringensis. 

Phenacomys gryci Repenning, n. sp. 

Figures 6 and 7 

Type Specimen.-VSNM 264295, a left lower first 

molar with moderate wear (fig. 6B). 

Etymology.-The species is named in honor of 

George Gryc, who has devoted four decades of his life 

to the geology and paleontology of northern Alaska. The 

species name is pronounced "gritchi." 

Type Locality.-Fish Creek Fauna near Harrison 

Bay, Alaska. Gubik Formation of Pliocene to Holocene 

age. 

Diagnosis.-A species of Phenacomys with only 

two accessory triangles in the anteroconid complex of the 

first lower molar, the lingual one broadly confluent with 

the highly variable anteroconid cap and the buccal one 

preserving a "Mimomys Kante" on the occlusal pattern 
0 2 3mm 0 

OCCLUSAL SCALE 

8 

2 

I 

BUCCAL SCALE 

3mm 

I 

Figure 5. First lower molars of Phenacomys deeringensis from the Cape Deceit Fauna, Seward Peninsula, Alaska, showing 

variability of occlusal pattern with wear. A, UA 768, a little-worn left molar. 8, UA 777, a moderately worn right molar. Individual variability occurs mainly in depth of wear required to reach a particular occlusal pattern. Note higher dentine tracts, 

greater occlusal pattern complexity with very little wear, and greater hypsodonty in comparison with Phenacomys gryci (fig. 6). 

Enamel pattern is essentially identical to that of living Phenacomys intermedius but tooth size is significantly greater and the 

pattern of little-worn teeth is modified with significantly less wear. The Cape Deceit Fauna is about 2.1 Ma old. Buccal views 

shown at a different scale than are occlusal views. 

in all but the least worn specimens (fig. 6); dentine tracts 

very short. Anteroposterior length of the first lower 

molars between 2.5 and 2.8 mm. 

Discussion.-This species is strikingly more primitive than Phenacomys deeringensis in having only two 

accessory triangles in the anteroconid complex in all stages 

of wear, in retention of the "Mimomys Kante" in nearly 

all stages of wear except in nearly unworn first lower 

molars, and in having very low dentine tracts. In these 

respects, Phenacomys gryci broadens the diagnosis of the 

genus to that given above. The teeth are lower crowned 

and smaller than in P. deeringensis, being about the size 

as in living Phenacomys intermedius. 

The "Mimomys Kante" is a relict of a structure of 

the anteroconid complex in primitive Mimomys species; 

it is preserved in most advanced species and derived 

lineages on the first accessory triangle on the buccal side 

of the anteroconid complex of the first lower molar. The 

"Mimomys Kante" is universally present in Phenacomys 

gryci, noted on only one specimen of Phenacomys deeringensis, and has not been observed in fossil or living 

Phenacomys intermedius or P. longicaudus. 

The anteroconid complex of living Phenacomys intermedius has four accessory triangles with about half or 

less wear and Phenacomys deeringensis has four accessory 

triangles with about one third or less wear, but only two 

accessory triangles are present in the anteroconid complex of Phenacomys gryci in the least worn (essentially 

unworn) first lower molars available for examination. Except in an essentially unworn condition (fig. 7), the anteroconid complex of Cromeromys has no accessory triangles 

clearly separated from the rest of the complex. The lesser 

dentine-tract height in P. gryci is obvious. However, the 

buccal location of the commissures between the posterior 

loop and the three basic triangles is clearly evident in the 

first lower molars (fig. 6) and the last upper molars (fig. 7) 

of all species of Phenacomys, unlike the basic pattern of 

Cromeromys (fig. 7). These trends suggest that the 

ancestry of Phenacomys lies in an unknown earlier form 

of the extinct Siberian genus Cromeromys. 

Genus Cromeromys Zazhigin 

'JYpe Species.-Cromeromys irtyshensis Zazhigin 

(1980). Cromeromys was discussed earlier in several 

reports by Zazhigin and by Gromov and Polyakov (1977). 

Range.- Cromeromys has been found in faunas 

ranging from Siberian Beringia to Kazakh S.S.R. The 

generic name is based upon Mimomys intermedius 

Newton ( = Mimomys savini Hinton) from the Cromerian 

of England, and the genus thus has a wide distribution 

Mammals of the Fish Creek Fauna 7 
8 

A 

0 0 

w 

..J 

<( 

u w CIJ ..J ..J <( <( u u CIJ u ..J :::> 2 <( co CIJ 

:::> 

..J 

u 

u 

0 2 

3mm 

c E 

3mm D 

Figure 6. First lower molars of Phenacomys gryci from the Fish Creek Fauna showing individual variability and variability with 

wear of the occlusal pattern. In relative order of increasing wear, specimens rank 8, C, A, 0, and E. Note strong tendency for 

elongation of lingual alternating triangles, and low dentine tracts on buccal side of teeth. A, Occlusal and buccal aspects of USNM 

264296. B, Occlusal and buccal aspects of the type specimen, USNM 264295. C-E, Occlusal aspects of USNM 264297, 264298, 

and 264299, respectively. Buccal views shown at a different scale than occlusal views. "Mimomys Kante" located by X. 

in Europe, although it is not generally recognized by 

European workers. 

Diagnosis.-Cromeromys is an arvicoline microtine 

rodent distinguished from other lineages of Mimomys, 

from which it is obviously derived, by the early loss of 

an enamel· islet in the anteroconid complex of the first 

lower molar; by the loss of a similar islet in the last upper molar, which instead has two well-developed reentrants 

on both buccal and lingual sides; by the early development of cementum deposited in the reentrant angles of 

the cheek teeth; by the retention of the "Mimomys Kante"; 

and by the lack of development of any clearly pinchedoff accessory triangles on the anteroconid complex. In 

addition, the last upper molars do not have a posteriorly 

elongate posterior loop with or without an enamel islet. 

Many of these characters are found in other lineages derived from or included in the genus Mimomys, but these 

other lineages differ in that these characters develop at 

8 Ancestry of Phenacomys and Arctic Borderland Biota 

a much later date than in Cromeromys. Thus, 

Cromeromys is a lineage that developed all of these 

relatively advanced features at an earlier period in history 

than did those lineages retained in the genus Mimomys; 

the consistency of these progressive features demonstrates 

a clear-cut divergence of this genus from the main evolutionary line of Mimomys. The commissures of the 

posterior loop and the three basic triangles of the first 

lower molar and the last upper molar are located along 

the sagittal midline of these teeth, and the anteroconid 

complex includes no well-separated accessory triangles, 

in contrast with Phenacomys. 

Discussion.-Interestingly, these precocious features 

in Cromeromys (except the development of cementum) 

also characterize many North American species of the 

genus Mimomys and, until recently, have been the reason 

for not recognizing Mimomys in North America; the 

genera Cosomys, Ophiomys, and Ogmodontomys have 
0 

A 

8 

0 

I 

2 

OCCLUSAL SCALE 

2 

I 

BUCCAL SCALE 

3mm 

E 

3mm 

I 

Figure 7. Cheek teeth of Cromeromys and Phenacomys. A, Little-worn right first lower molar of 

Cromeromys ex gr. intermedius from the Beteke Fauna southwest of Petropavlovsk, Kazakh S.S.R., 

in occlusal and buccal aspects; between 3.7 and 4.2 Ma old. B-E, Right last upper molars. B, 

Cromeromys sp. from the Kartashovo Fauna along the lrtysh River northeast of Omsk, U.S.S.R.; 

Beteke age. C, Phenacomys gryci from the Fish Creek Fauna (USNM 264300). 0, Phenacomys deeringensis from the Cape Deceit Fauna, Seward Peninsula, Alaska; 2.1 Ma old. f, Phenacomys intermedius from Glacier National Park, Montana; modern. A and B redrawn from Zazhigin (1980) 

and D, from Guthrie and Matthews (1971 ); their scale is only approximate. Note that earliest known 

representatives of Cromeromys already possess some cementum in reentrant angles and that dentine tract development is greater than in Phenacomys gryci (fig. 6). "Mimomys Kante" of Cromeromys 

located by X. 

been used instead. However, the earliest forms of 

Mimomys in North America [M. ( Ophiomys) mcknighti 

(Gustafson) and M. (Cosomys) sawrockensis (Hibbard)] 

do have the enamel islets and a Mimomys-like last upper 

molar. These features were lost early in the North 

American history of the genus, and they cannot be derived 

from the Eurasian genus Cromeromys. Cromeromys conceivably derives from the North American Mimomys 

lineage. 

Except for the central commissures between the dentine fields, the lack of accessory triangles in the 

anteroconid complex, and the presence of cementum only 

Mammals of the Fish Creek Fauna 9 
... 

Q 

> 

n = 

I'D 

II> 

s 

S, 

~ I'D 

:::1 

~ 

a 

3 

~ 

~ 

= c. 

> a 

;:;· 

= 0 

a. 

~ 

D:i' 

= c. 

= (5' 

;::-

SPECIES DIVERSITY 

K , , __ ,..,_, ···-- rl ~I I I I I I I I I 

I I-

---------- -I I- - <( 

z 

:::> 

<( 

u. 

w 

~ I I- ~ -I ~ 

w 

a: 

u 

:::t 

~ I r .............. -I 1- ............... w 

(!) 

::5 

al 

~ I I- '""""- ~ 1- '""""- (/) 

(/) 

<( 

i 

I 

I~ A 

I ~ 

~ ~ 

A 8 

2 4 6 8 10 0 20 40 60 80 

NUMBER OF SPECIES NUMBER OF VALVES 

n f\: I 

-I 1---

-I ~ 

-I f+-

-I r\ 

~ ~I I v 

100 0 

.... y .... - .,,.~ 

I 

80 

NUMBER OF SPECIMENS 

I 

-l 

-I 

-I 

-I 

~ I 

\ I ··-····r ...... _ "· ..... I 110 

I+ --19 

we ~8 

1- .............. -17 

1- .............. -16 

~ ~ +~ .v I 

4 

3 

2 

~---L----~--~~---L--~0 

0 20 40 60 80 1 00 

NUMBER OF SPECIMENS 

Figure 8. Plot of ostracode abundance and species diversity in the Fish Creek section. A, Species diversity. B, Total abundance of specimens, shown in number 

of valves; adults and juveniles have been combined. C, Abundance of specimens of marine taxa, shown in number of valves. 0, Abundance of specimens of nonmarine taxa, shown in number of valves. 
in Cromeromys, the genus would conform to the diagnosis 

of Phenacomys given here. The first two are primitive 

characters, suggesting that Cromeromys was ancestral to 

Phenacomys. The presence of cementum in Cromeromys, 

although rudimentary in the earliest known form (fig. 7), 

suggests that the divergence of Phenacomys (which lacks 

cementum) from Cromeromys took place earlier than the 

oldest known record of Cromeromys, between 3.7 and 

4.2 Ma old. In addition, Phenacomys gryci has less progressive dentine tract development than the earliest known 

Cromeromys (figs. 6, 7), further suggesting a branching 

of Phenacomys from Cromeromys at an early date. 

Thus, the inferred phylogeny of Phenacomys began 

with an origin, more than 4 million years ago, from a 

notably progressive branch of Mimomys, called 

Cromeromys, by development of an almost static rate of 

evolution of those primitive characters retained in the 

Phenacomys lineage. Living Phenacomys still has not 

developed rootless teeth or cementum; Phenacomys gryci, 

although clearly younger, has dentine tracts that approximate those of Mimomys of about _4 to 4.5 Ma ago, and 

the genus still retains today an upper last molar that is 

like that of Cromeromys. In contrast, Phenacomys has 

progressively increased the number of alternating triangles 

in the anteroconid complex of the first lower molar, unlike 

Cromeromys and some living descendants of Mimomys, 

as, Arvicola. Arvico/a itself may have derived from 

Cromeromys intermedius (equals Mimomys savim) as 

recently as 400,000 years ago. 

OSTRACODES OF THE FISH CREEK SECTION 

Marine and nonmarine ostracodes from the Fish 

Creek sediments (pl. 1) can be divided into two distinct 

assemblages that differ from each other in age and in environment of deposition. A basal assemblage is present 

in the lowest meter of the 4-m-thick lower silt unit, and 

an upper assemblage (the Fish Creek Fauna) is present 

in the upper 0.3 m of the lower silt unit and throughout 

the medial sand unit and into the upper unit (figs. 3, 8; 

table 2). These two assemblages are separated by 2 m of 

the lower silt unit from which no ostracodes have been 

recovered. 

Basal Assemblage 

The basal ostracode assemblage contains three 

marine taxa, Pterygocythereis n. sp., Loxoconcha venepidermoidea Swain, and Paracyprideis pseudopunctillata 

Swain, and one nonmarine species, Cytherissa lacustris 

(Sars) (table 1). Specimen abundance is low (fig. 8B}, consisting of two adults and four juveniles, all very well 

preserved; the small number of specimens indicates that 

reworking cannot be totally ruled out. Pterygocythereis n. 

sp. is an unusual, highly distinctive taxon with no known 

occurrence in Pleistocene North Slope sediments or in 

modern shelf environments of the Arctic circumpolar 

region. The species is an extinct one that occurs only in 

older sediments of the Arctic Ocean. Pterygocythereis n. 

sp. has recently been identified from a small number of 

sites in the eastern coastal plain of Alaska. It occurs at 

these sites exclusively as an element of a deeper water 

fauna (middle to outer shelf), which is composed of taxa 

known previously only from the northeast Atlantic. 

Pterygocythereis n. sp. also has been found recently at 

several localities near Harrison Bay (fig. 9A) in a distinctive assemblage consisting of Rabilimis paramirabilis and 

a large number of extinct Cytheropteron and cytherideid 

species. Rabilimis paramirabilis has been identified from 

18m depth in a shothole at Fish Creek (Swain, 1963) that 

is geographically very close to the locality that we report 

on herein (fig. 9A). 

Pterygocythereis n. sp. is known from deposits at 

least as old as the presumed middle Miocene-lower 

Pliocene Nuwok Member of the Sagavanirktok Formation of the Marsh anticline (Barter Island and Manning 

Point) to the east (fig. 1), where it recently has been 

found. The co-occurrence (fig. 10) of Pterygocythereis 

n. sp. with Rabilimis paramirabilis at localities near Fish 

Creek is the principal argument for an age less than 3 

Ma for the basal Pterygocythereis assemblage at Fish 

Creek. Rabilimis is closely related to Echinocythereis 

based on valve shape, hinge type, muscle scar arrangement, and ornamentation, but Rabilimis is larger than 

any known species of Echinocythereis, with no intermediate forms known. Rabilimis is thought to have 

arisen from the Echinocythereis stock of the North Atlantic Ocean (fig. 11) in the late Pliocene (J.E. Hazel, oral 

commun., 1985). The oldest known Rabilimis species is 

R. paramirabilis (Swain, 1963), first identified from 

sediments in shotholes taken in the central and western 

Arctic Coastal Plain. Hazel (written commun., 1968) 

identified R. paramirabilis in dredge and core sediments 

from the Seward Peninsula (fig. 2); these sediments have 

been defined as Beringian by Hopkins (1967), and are between 3 Ma (opening of Bering Strait) and 2.48 Ma 

(Gauss-Matuyama boundary) old. Hazel (1967, p. 38) 

mentioned the modern occurrence of Rabilimis 

paramirabilis off Point Barrow. However, Hazel (oral 

and written commun., 1985) has pointed out that this occurrence was the result of a clerical error on a checklist 

prepared during study for the 1967 paper. Rabilimis 

paramirabilis apparently evolved in the Alaskan region, 

as the species has not been recorded elsewhere. 

Rabi/imis paramirabilis, thought to have evolved 

directly from Echinocythereis, is the ancestral species in 

the Rabilimis lineage (figs. 10, 11), and gave rise to 

Rabilimis septentrionalis and Rabilimis mirabilis in postBeringian time. Rabilimis septentrionalis is known back 

to Anvilian time (about 2.2 Ma; Brouwers and others, 

Ostracodes of the Fish Creek Section 11 
A 

0 

I 

0 

I 

5 

5 

I I 

10 

10 

I I 

15 

I 

20 

Harrison Bay 

15 20 25 MILES 

25 KILOMETERS 

Figure 9 (above and facing page). Localities and zoogeographic distribution of Pterygocythereis n.sp. and Rabilimis species 

used for this study. A, Localities of Gubik Formation in vicinity of Fish Creek in which older assemblages of ostracodes have 

been identified. Circle, locality in which both Pterygocythereis n. sp. and Rabilimis paramirabilis were identified. Triangle, locality 

in which only Rabilimis paramirabilis was identified. Square, Fish Creek section in which only Pterygocythereis n. sp. was identified, and Ocean Point section. Ocean Point section contains no distinctive ostracodes; the few taxa present represent longranging shallow-water forms. B, Modern zoogeographic distribution of the two living Rabilimis species. R. mirabilis prefers middle to outer sublittoral water depths, and occurs in cold temperate to frigid marine climates. R. septentrionalis is a shallowwater form, preferring inner sublittoral environment; occurs predominantly in the frigid marine climate, although also present 

in subfrigid marine climate of Norton Sound. Data from Hazel (1970) and Neale and Howe (1975). 

12 Ancestry of Phenacomys and Arctic Borderland Biota 
B 

EXPlANATION 

• Rabilimis septentrionalis 

e Rabilimis mirabilis 

1984), being present in all the Gubik transgressive cycles 

except the Beringian. There is one possible exception along 

the Colville River south of Ocean Point at LDC locality 

78 ACr 113, where several specimens of Rabilimis septentrionalis are found in sediments for which an older amino 

acid ratio has been determined. In addition, geomorphic 

and depositional relationships appear to indicate an older 

age (Carter and Brigham-Grette, in press). At present 

evidence is insufficient to explain the apparent discrepancy. Rabilimis mirabilis is known back to Kotzebuan time 

(possibly 240,000 years ago, Brouwers and others, 1984), 

occurring predominantly in upper Pleistocene sediments 

in Alaska. Rabilimis mirabilis is a deeper water form 

(greater than 20 m, middle to outer shelf), and most of 

the onshore Gubik Formation represents shallow, inner 

sublittoral water depths; therefore, any earlier Pleistocene 

occurrences of Rabilimis mirabi/is are likely to be preserved in offshore sediments. The modern distribution of 

Rabilimis is shown in figure 9B and that of Echinocythereis in figure 12A. 

The most convincing argument in support of the 

Rabilimis lineage is seen in the adductor muscle scar pattern (fig. 11). Hazel (1967) demonstrated the taxonomic 

stability and utility of the frontal and adductor scar pattern in hemicytherid and trachyleberid ostracode genera, 

and showed that the pattern tends to become more complex through time within a lineage. The lineage of 

Echinocythereis - Rabilimis paramirabilis - Rabilimis 

Ostracodes of the Fish Creek Section 13 
0.01 Ma 

0.5 

1.0 

1.7 

2.4 

5.2 

HOLOCENE 

w 

z 

w 

u 

0 

1-

CJ) 

jjj 

...J 

a.. 

w 

z 

w 

u 

0 

::::i 

a.. 

MIOCENE 

PACIFIC 

.~ 

0 

s::: 

0 

·;: 

!:: 

~ 

g. 

"' ex: 

NORTH 

ATLANTIC 

~ 

.:c; ~ l: c ·e s::: 

0 

ex: ·;: 

!:: 

cu 

~ 

"' ci. ex: a. 

(/) 

-~ 

~ cu 

..c: 

"'5. 

u 

0 

Ol 

2' 

cu 

tt 

ARCTIC 

~ .:c; 

l: ~ "' ·e s::: 

ex: .g 

!:: ci. I~ (/) 

,g. c:: 

I ~ "' I~ -~ 

cu 

I ..c: 

I "'5. 

u I 0 

Ol - I 2' 

A 

I 

L~ ct 

~ 

.:c; - B 

l: "' ·e ~ -~ 

cu l: 

1 tj c 

Q, f.-

ex: ..c:a. 

ua. 

LL.lUl 

c 

Figure 10. Stratigraphic range of the three Rabilimis species 

in Pacific (Norton Sound), North Atlantic, and Arctic Oceans. 

Known Neogene stratigraphic range of Pterygocythereis in North 

Atlantic and Arctic Oceans is also plotted. Dashed portion of 

a range, uncertainty in exact time of origin of the taxon. 

A Approximate position of Fish Creek Fauna (upper ostracode 

assemblage). 

B Approximate position of lower ostracode assemblage in Fish 

Creek section. 

C Approximate position of Marsh Creek anticline ostracode 

assemblage. 

septentrionalis shows the two median adductor scars splitting from two to three to four scars, respectively. Rabilimis 

mirabilis maintains a more conservative pattern by retaining only three median scars. 

The presence of Pterygocythereis n. sp. is also important for understanding the paleoenvironment, which 

indirectly provides information about the age range of the 

basal assemblage. Pterygocythereis ranges from the Paleocene through the Holocene, occurring commonly throughout the subtropical and temperate northern Atlantic 

Ocean and rarely in the subfrigid Norwegian Sea (fig.l2B). 

In the northwestern Atlantic Ocean, Pterygocythereis occurs in the southern part of the cold temperate zone, but 

apparently does not live in the northern cold-temperate 

or subfrigid zones of the western North Atlantic (fig. 12B). 

Pterygocythereis n. sp. is related to European forms of 

the genus and not to the more temperate northwest Atlantic P. americana - P. inexpectata lineage. The presence of 

Pterygocythereis suggests that warmer conditions existed 

during deposition of the lower Fish Creek assemblage than 

the modern frigid temperatures that are present today. 

14 Ancestry of Phenacomys and Arctic Borderland Biota 

Upper Assemblage-The Fish Creek Fauna 

The upper ostracode assemblage, part of the Fish 

Creek Fauna, is much more diverse and abundant than 

the basal assemblage (table 1; fig. SA, B). Eleven marine 

species and six nonmarine species occur in the nearly 6 m 

that include the uppermost part of the lower silt unit, the 

marine/estuarine medial sand unit, and part of the upper silt unit of the Fish Creek section (fig. 3). Diversity 

and abundance have three distinct peaks at 5.75 m, 7.7 m, 

and 8.8 m above the base of the exposure (samples 

84-EB-178, -180, and -183, respectively). The peak at 

5.75 m contains a mixture of marine and nonmarine taxa, 

with the nonmarine species dominating in abundance. The 

sample at 5.75 m is dominated by eurytopic shallow 

marine to marginal marine taxa. The ostracode composition and the known modern tolerances of the individual 

species support the interpretation of a tidal channel setting with associated estuarine and nearshore marine 

deposits as suggested by the sedimentary structqres. The 

peaks at 7. 7 m and 8.8 m correspond to the two upper 

shell beds (fig. 3); the upper of these shell beds is the 

source of the microtine remains. The ostracode assemblages in the shell beds are dominantly marine (fig. 8C), 

consisting of well-preserved, intact valves. The shell beds 

are composed of concentrations of mollusks, detrital 

wood, and gray sand. Most of the ostracode species are 

represented by adults, but some juveniles are also present, 

suggesting a small amount of differential transport and 

(or) destruction of juveniles versus adults. The ostracode 

species composition in the shell beds suggests a nearshore, 

predominantly marine environment, such as a beach or 

bar. 

The nature of the marine environment indicated by 

the upper assemblage (the Fish Creek Fauna) is considerably different from that of the basal assemblage. The 

upper assemblage taxa are indistinguishable from a 

modern Arctic Ocean assemblage, containing mostly extant species characteristic of frigid to subfrigid marine 

temperatures. Rabilimis septentrionalis (Brady), Loxoconcha venepidermoidea Swain, and Cytheretta 

teshekpukensis Swain do not live south of Norton Sound 

(fig. 2) today. 

The age of the upper ostracode assemblage can be 

constrained by the presence of R. septentrionalis, which 

implies a post-Beringian age. The taxa present thus range 

from the late Pliocene through the Holocene. 

MOLLUSKS OF THE FISH CREEK FAUNA 

Late Cenozoic mollusks in the Fish Creek Fauna 

(table 2) show clearly that these deposits were formed after 

the opening of Bering Strait. All but one of the species 

is extant, and the sum of their modern distributions 
Table 1. Ostracode species present at Fish Creek 

Lower Upper assemblage 

-~ssemblage (Fish Creek Fauna) 

Samples ------------------------- 171 172 60a 60b 178 60f 180 181 60c 183 184 182 185 186 

Marine taxa 

Pterygocythereis n. sp ----------- X X 

Loxoconcha venepidermoidea ---- X X X X 

Paracyprideis pseudopunctillata --- X X X X X X X X 

Cytheromorpha macchesneyi ----- X X 

Cytheropteron montrosiense ------ X 

Cytheretta teshekpukensis -------- X X X X X X 

Heterocyprideis sorbyana -------- X X X X X X 

Normanicythere leioderma ------- X 

Rabilimis septentrionalis --------- X X X X X X X X X 

Sarsicytheridea bradii ----------- X X X 

Cytheropteron pyramidale ------- X X X 

Sarsicytheridea punctillata ------- X X 

Robertsonites tuberculata -------- X X X 

Acanthocythereis dunelmensis ---- X 

Nonmarine taxa 

Cytherissa lacustris ------------- X 

Limnocythere spp ---------------

Candona spp -------------------

Cyprid ------------------------

indicates a marine climate warmer than now occurs in 

northern Alaska. Further, the mollusks lived in shallow 

water, at or very close to shoreline. 

Among the 43 species-level molluscan taxa present 

at Fish Creek (table 2), 22 (51 percent) have their earliest 

stratigraphic records in the Pacific, 3 (7 percent) occurred 

first in the Atlantic, and 18 (42 percent) have histories too 

poorly known to show provenance. If the Bering Strait 

had not yet been opened when the Fish Creek strata were 

laid down, half of the known molluscan fauna would be 

absent. Most of the Fish Creek mollusks have modern 

geographic ranges that extend into the Arctic Ocean. 

However, the bivalve Clinocardium californiense and the 

gastropods Aforia circinata and Littorina squalida now 

live only south of Bering Strait. In addition, the ranges 

of the Pacific gastropods Admete regina, Liomesus 

ooides, and Neptunea beringiana (tentatively identified 

here) now extend northward only to the Chukchi Sea. 

Because molluscan stratigraphic ranges within the Gubik 

Formation are not yet well documented, the molluscan 

fauna does not help to assign the Fish Creek deposits to 

a particular interval within the Gubik. The Fish Creek 

mollusks clearly show, however, that this fauna lived after 

the Late Cenozoic opening of Bering Strait that allowed 

Pacific species to migrate into the Arctic Ocean. 

Except for the bivalve Axinopsida orbiculata and 

the extinct gastropod Neptunea lyrata leffingwelli (tentatively identified here), all the Fish Creek mollusks 

X 

X 

X 

X X X X X X X 

X X X X X 

X X X X X X X 

X X X 

currently range south of Bering Strait. The mollusks of 

the Fish Creek Fauna represent a cold-temperate to subfrigid marine climate, such as exists today in the southern 

Bering Sea and northern Gulf of Alaska, distinctly 

warmer than the modern marine climate off northern 

Alaska. The relatively warmer marine climate during Fish 

Creek time is also suggested by the presence of Littorina 

squalida, an intertidal to shallow subtidal gastropod that 

cannot tolerate thick accumulations of sea ice, which can 

occur virtually year round along the northern Alaskan 

coastline today. This species lives as far north as lat 65 o:30' 

N., on the western Seward Peninsula south of Bering Strait 

(Foster, 1981); it does so apparently by living subtidally 

below the relatively thin ice cover during the colder part 

of the year, then repopulating the intertidal zone during 

the warmer summer months (Joseph Rosewc:ter, written 

commun., 1984). The large adult size of the Fish Creek 

individuals, comparable to modern L. squalida, suggests 

that they lived for several years at the Fish Creek site and 

did not occur there as a result of a single summer's migration. Modern littorines live for about 3 or 4 years, and 

it is doubtful that larger individuals could reach their full 

growth in a single year (Joseph Rosewater, written commun., 1984), especially in the colder northern reaches of 

the species' range. 

The presence of abundant L. squalida in the Fish 

Creek Fauna also indicates that a shoreline was nearby, 

because this species lives in the intertidal and shallow 

Mollusks of the Fish Creek Fauna 15 
w 

z 

w 

u 

g 

0 

::c 

w 

z 

w 

u 

0 

1-

(/) 

w 

....1 

0.. 

•• 1. •• • 

-

' R. mirabilis \ R. septentrionalis 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

w 

,. ' R. paramirabi/is z 

w •• u 

0 

:::i ,. 0.. I 

I 

I Rabilimis 

Echinocythereis 

w 

z 

w 

u 

0 

~ 

• • ,. • 

• • I 

Figure 11. Sketches of adductor muscle scar pattern from right valves of Rabi/imis and Echinocythereis and scanning electron micrographs illustrating lateral view of male left valves. General evolutionary trend of adductor muscle 

scars within ostracode lineages is for increased complexity through time (Hazel, 1967), clearly illustrated in trend 

of two median scars splitting from two scars in Echinocythereis to three scars in Rabilimis paramirabilis, and, finally, to four scars in R. septentrional is. R. mirabilis is apparently more conservative, retaining three median adductor 

scars. Dashed lines, uncertainty in exact time of origin of taxon. Note that magnification of Rabilimis specimens 

and that of Echinocythereis specimen are different. Echinocythereis scar pattern from Hazel (1967). Echinocythereis 

specimens are from the collections ofT. Cronin, USGS, Reston, Virginia. Rabilimis scar patterns from personal 

observations (EMB) and from written communication of K.G. McKenzie to j.E. Hazel (1968). Scale bar= 100 JLm. 

subtidal zones. The remainder of the Fish Creek mollusks 

also clearly indicate a shallow marine habitat. The bivalves 

Astarte borealis, Hiatella arctica, Mya truncata, and 

16 Ancestry of Phenacomys and Arctic Borderland Biota 

Serripes groenlandicus, and the gastropods Boreotrophon 

pacificus and Plicifusus kroyeri have their upper bathymetric limits in the intertidal zone. Further, of the 31 Fish 
Table 2. Origins of Fish Creek mollusks 

Bivalves 

Astarte borealis (Schumacher) -----------------------------------

A. esquimalti (Baird) -------------------------------------------

Axinopsida orbiculata (Sars) ------------------------------------

Clinocardium californiense (Deshayes) ----------------------------

C ciliatum (Fabricius) ------------------------------------------

Cyclocardia crassidens (Broderip & Sowerby) ----------------------

C crebricostata (Krause) ----------------------------------------

Cyrtodaria kurriana Dunker -------------------------------------

Hiatella arctica (Linnaeus) --------------------------------------

Liocyma fluctuosa (Gould) --------------------------------------

Macoma cf. M brota Dall --------------------------------------

M balthica (Linnaeus) ------------------------------------------

Mya truncata Linnaeus -----------------------------------------

~uculana radiata Krause) ---------------------------------------

N. cf. N. minuta (Fabricius) -------------------------------------

Serripes groenlandicus (Bruguiere) --------------------------------

Yoldia myalis Couthouy ----------------------------------------

Gastropods 

Admete couthouyi (Jay) ----------------------------------------

A. regina Dall -------------------------------------------------

Aforia circinata Dall -------------------------------------------

Amauropsis islandica (Gmelin) ----------------------------------

Boreotrophon clathratus (Linnaeus) ------------------------------

B. pacificus Dall -----------------------------------------------

B. truncatus (Stroem) -------------------------------------------

Buccinum cf. B. plectrum Stimpson ------------------------------

B. polare Gray -------------------------------------------------

Co/us pubescens Verrill -----------------------------------------

C spitzbergensis (Reeve) ----------------------------------------

Epitonium greenlandicum (Perry) --------------------------------

Liomesus ooides Middendorff -----------------------------------

Littorina squalida Broderip & Sowerby ---------------------------

~atica clausa Broderip & Sowerby -------------------------------

~eptunea cf. N. beringiana (Middendorff) ------------------------

N. cf. N. lyrata leffingwelli Dall ---------------------------------

N. heros heros (Gray) -------------------------------------------

Obesotoma cf. 0. laevigata (Dall) --------------------------------

Oenopota cf. 0. arctica (Adams) ---------------------------------

Plicifusus kroyeri Moeller ---------------------------------------

Polinices pallidus (Broderip & Sowerby) ---------------------------

Retusa umbilicata (Montagu) ------------------------------------

Tachyrhynchus erosus (Couthouy) --------------------------------

Trichotropis borealis Sowerby ------------------------------------

T. bicarinatus (Sowerby) ----------------------------------------

Pacific 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

Atlantic Unknown 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

Creek mollusks with documented modern bathymetric 

ranges, 15 species have their shallowest occurrences in the 

0-10 m range, 21 occur as shallow as the 0-20 m range, 

and all but two species are found in 0-50 m depths. 

At Fish Creek no mollusks were seen in life orientations. All bivalves were disarticulated and most mollusks 

show breakage and abrasion. However, abundant 

unbroken specimens of extremely delicate species such as 

Axinopsida orbiculata and Retusa umbilicata suggest that 

the post mortem transport of the mollusks was not extensive. Redeposition of the mollusks is likely to have occurred shortly after death by waves or currents, instead 

of by reworking of specimens preserved in an earlier 

Gubik transgressive deposit. 

Mollusks of the Fish Creek Fauna 17 
EXPlANATION 

& Echinocythereis procteri 

• Echinocythereis margaritifera 

• 

• 

A 

Figure 12 (above and facing page). Zoogeographic distribution of Echinocythereis and Pterygocythereis species in this study. 

A, Modern zoogeographic distribution of the three living Echinocythereis species in the North Atlantic. Echinocythereis, presumed 

ancestor of Rabilimis, can live only in warmer water environments than exist in the Arctic today. Data from Hazel (1970). B, 

Modern zoogeographic distribution of the three living Pterygocythereis species. These occurrences clearly illustrate that 

Pterygocythereis does not live in frigid marine climate of modern Arctic Ocean. Pterygocythereis n. sp. found at Fish Creek 

is related to Pterygocythereis mucronata - P. jonesii species complex, lacking dorsal crest of P. inexpectata species complex. 

Data from Hazel (1970) and Neale and Howe (1975). 

FLORA OF THE FISH CREEK SECTION 

Sixteen sediment samples collected at Fish Creek in 

1983 by E.M. Brouwers for ostracode analysis were also 

subsampled and processed for palynological study. Ten 

of the samples contained pollen and spores, but only four 

contained palynomorphs in sufficient number to permit 

quantitative analysis (fig. 3). These four samples (table 

3; 83-EB-174, -176, -179, -180) selected for detailed study 

18 Ancestry of Phenacomys and Arctic Borderland Biota 

contained few reworked palynomorphs, whereas theremaining six contained a high proportion of reworked 

pollen and spores, mostly of Late Cretaceous age. None 

of the useful pollen samples came from the lower 3 m of 

the medial sand unit with bedding suggestive of tidal 

channels. 1\vo samples from the upper meter of the lower 

silt unit (approximately 3 m above the basal ostracode 

assemblage) and two samples from the upper 1.5 m of 

the medial gray sand unit (approximately 3.5 m above the 
B 

EXPIANA TION 

A Pterygocythereis mucronata 

• Pterygocythereis inexpectata 

e Pterygocythereis jonesii 

lowest ostracodes included in the Fish Creek Fauna and 

1.5 m below the principal mollusk and mammal beds) 

were analyzed for pollen and spore content. The results 

of those analyses are presented in table 3. The two samples 

from the lower unit have comparatively abundant pollen 

of Betula (birch), Ericaceae (for example, blueberry), and 

Cyperaceae (sedge). Pollen of conifers, particularly Picea 

(spruce) and Pinus (pine), is present in significant 

amounts, along with very small amounts of Larix (larch) 

and Abies (fir). None of these conifers now grows on the 

North Slope of Alaska (Viereck and Little, 1972). Picea 

glauca (white spruce) and P. mariana (black spruce) reach 

as far north as the valleys on the south flank of the Brooks 

Range and eastward to the Mackenzie Delta in Canada. 

Larix laricina (larch or tamarack) grows south of the 

Brooks Range along much of the Yukon River and some 

of its tributaries. The nearest species of Pinus is P. contorta (lodgepole pine), now found in the southeastern 

Yukon Territory and areas to the south; in Alaska, it now 

lives only in the "panhandle" region to the southeast. 

Pinus banksiana (Jack pine) grows far to the southeast 

in Northwest Territories. Abies spp. grow as far north as 

Juneau in the Alaska "panhandle" region. The conifer 

assemblage from the lower unit at Fish Creek is similar 

to that described by Nelson (1979, 1981) and Nelson and 

Carter (1985) from the lower (marine) part of the Gubik 

Formation at Ocean Point, 16 miles (25 km) to the 

southeast of the Fish Creek section, on the Alaskan North 

Slope. Nelson compared the Ocean Point pollen flora 

from this lower unit with that of modern Anchorage, 

although some components of this pollen flora now have 

northern limits well to the south of that city. However, 

Flora of the Fish Creek Section 19 
not enough is yet known about Pliocene vegetation of 

the Arctic Ocean Borderland to be certain of the 

significance of modern analogs. Pliocene vegetation probably included at least some, and perhaps many, species 

that differ taxonomically and ecologically from the 

modern analogs. 

The variety of fossil pollen from Fish Creek is sufficiently similar to that represented by pollen from surface samples in Alaska and Canada to permit some broad 

interpretations of paleovegetation. The two samples from 

the lower unit most probably represent a vegetation 

roughly equivalent to present-day shrub tundra ("moist 

tundra" of Viereck and Little, 1972, as differentiated 

from "wet tundra"). The significant percentages of 

Betula, Ericaceae, Cyperaceae, along with Salix and 

assorted taxa of herbaceous plants such as 

Caryophyllaceae, Valeriano, Artemisia, and Tubuliflorae 

are strongly suggestive of shrub tundra vegetation, such 

as that found today in the Arctic Foothills of the Brooks 

Range. The percentages of Picea and Pinus pollen are 

higher in the fossil assemblages of the lower unit at Fish 

Creek than in most surface pollen samples that have been 

reported from northern Alaska (for example, Nelson, 

1979; Livingstone, 1955; Moriya, 1978), but a few surface samples have been described (Nelson, 1979) from the 

Arctic Coastal Plain that contain high percentages of conifer and shrub pollen, transported by wind long distances 

from sources to the south and southeast. That such pollen 

predominates in those few samples may be due to the low 

pollen production of local tundra vegetation that does 

not mask the accumulation of long-distance transported 

pollen. This contrasts to the situation in boreal or 

temperate vegetation communities where relatively high 

pollen production masks wind-transported pollen from 

distant sources. It remains unclear, however, why the 

percentage of conifer pollen is so highly variable in 

modern surface samples in northern Alaska. 

The presence of Pinus and Picea pollen in the Fish 

Creek samples can be interpreted in two ways. The 

relative abundance of conifer pollen in the lower unit at 

Fish Creek may indicate that the northern edge of the 

boreal forest was farther north than at present, or it may 

indicate differences in prevailing wind patterns that 

favored long distance transport of these conifer pollen 

types. It is most likely that conifers, including Picea, 

Pinus, Abies, and Larix, grew north of their present 

limits, probably growing on the north side of the Brooks 

Range in the Arctic Foothills. Forests may have been 

restricted to river valleys rather than forming a continuous forest cover. However, it seems unlikely that 

forest vegetation existed as far north as Fish Creek at the 

time of deposition because the percentages of conifer 

pollen are more suggestive of tundra (Birks, 1973). 

Pollen samples from the upper part of the medial 

gray, organic-rich sand unit containing the Fish Creek 

Fauna (table 3) also contain Cyperaceae, Gramineae, 

20 Ancestry of Phenacomys and Arctic Borderland Biota 

Salix, Ericaceae, Betula, and most of the herbaceous taxa 

and spore types found in the lower unit. Picea and Pinus 

are present, but in significantly smaller amounts than in 

the lower unit. The uppermost sample (83 EB 180}, a little more than 1 m below the fossil microtine bed, contains the lowest percentages of conifer pollen, as well as 

of pollen of Betula, Ericaceae, and Gramineae, and a 

much higher percentage of Cyperaceae pollen, suggesting 

herb tundra (wet tundra of Viereck and Little, 1972}, 

rather than shrub tundra, and progressive southward 

retreat of conifer forests from the Arctic Foothills and 

shrub tundra from the Arctic Coastal Plain. Nevertheless, 

the climate may have been somewhat milder than that 

of the present day in the coastal plain or foothills, because 

Nuphar (water lily) pollen is present in the samples from 

the Fish Creek Fauna. Nuphar is not known today north 

of the Brooks Range (Hulten, 1968). The shift from shrub 

tundra vegetation to herb tundra vegetation may reflect 

more localized vegetation changes resulting from poor 

drainage. There is a trace of Larix pollen in sample 83 

EB 180. Because Larix is poorly represented in most 

pollen records, the presence of even a small amount of 

Larix pollen suggests the possibility of some larch trees 

in the area. The presence of Larix wood in the deposits 

strengthens that possibility (Carter and Galloway, 1985); 

however, it is possible that the pollen was reworked from 

older deposits or transported a long distance by wind or 

water and that the wood is driftwood. 

In sum, the pollen evidence suggests that during 

that part of the Pliocene represented by the Fish Creek 

section, tundra vegetation covered the Arctic Coastal 

Plain. During deposition of the lower unit, conifer forests 

containing spruce, pine, fir, and larch may have grown 

as far north as the Arctic Foothills south of Fish Creek. 

Shrub tundra vegetation covered the Arctic Coastal Plain 

near Fish Creek. Later, during deposition of the strata 

containing the Fish Creek Fauna, conifer forests were 

probably farther to the south and the vegetation of the 

coastal plain changed to wetland herbaceous tundra. This 

suggests climatic cooling and a shift to wetter habitats, 

possibly because of the development of permafrost, but 

during deposition of the Fish Creek Fauna it does not 

appear to have gotten as cold as it is today on the North 

Slope. 

CORRELATION IN THE 

ARCTIC OCEAN BORDERLAND 

Age of the Fish Creek Fauna 

The evolution of the Phenacomys and Synaptomys 

lineages of microtine rodents, the approximate 3.0 Ma 

opening of the Bering Strait with introduction of mollusks 

of Pacific origin into the Arctic Ocean (Gladenkov, 1981 ), 
Table 3. Pollen and spore counts of four samples from Fish Creek 

Lower unit 

Sam pie No. ----------------------------------- 83-EB-174 83-EB-176 

Upper unit 

(Fish Creek Fauna) 

83-EB-179 83-EB-180 

Tree and shrub pollen (in percent) 

Picea (spruce) ------------------------------

Pinus (pine) --------------------------------

Larix (larch) --------------------------------

Abies (fir) ----------------------------------

Betula (birch) ------------------------------

A /nus (alder) -------------------------------

Populus (poplar) ----------------------------

Salix (willow) -------------------------------

Ericaceae (such as blueberry) -----------------

8.7 

8.7 

0.0 

0.0 

36.7 

4.2 

0.0 

2.3 

13.6 

6.7 

13.8 

0.4 

1.1 

34.7 

1.5 

0.4 

2.2 

18.7 

2.3 

6.0 

0.0 

0.0 

32.3 

4.7 

0.0 

0.0 

11.7 

1.3 

1.1 

Tr. 1 

0.2 

5.9 

1.6 

0.0 

0.9 

5.5 

Herb pollen (in percent) 

Cyperaceae (sedge) --------------------------

Gramineae (grass) ---------------------------

Artemisia (wormwood) ----------------------

Thbuliflorae (aster type) ---------------------

Liguliflorae (dandelion type) -----------------

Cruciferae (mustard family) ------------------

Caryophyllaceae (pink family) ----------------

Valeriana ----------------------------------

15.2 

4.9 

0.8 

2.3 

0.0 

0.8 

0.8 

0.0 

10.8 

2.2 

1.1 

3.0 

0.4 

0.4 

1.1 

0.4 

20.0 

14.0 

0.0 

2.0 

0.3 

0.0 

2.7 

0.3 

72.3 

7.3 

0.5 

0.6 

0.0 

0.0 

0.3 

0.2 

Aquatics (in percent) 

Nuphar (water lily) -------------------------- 0.0 0.0 0.3 Tr. 1 

Total pollen count ------------------------ 264 268 300 640 

Spore types (in percent) 

Equisetum (horsetails) -----------------------

Lycopodium (club moss) ---------------------

Polypodiaceae (ferns) ------------------------

Se/agine//a sibirica (spike moss) ---------------

Sphagnum ---------------------------------

Total pollen and spore count ---------------

0.0 

3.1 

2.8 

0.0 

26.0 

388 

0.0 

1.4 

1.9 

1.1 

23.0 

369 

0.0 

0.6 

0.3 

0.0 

5.3 

320 

0.3 

1.8 

1.0 

Tr. 1 

5.3 

699 

Algae types (in percent) 

Pediastrum ---------------------------------

Botryococcus -------------------------------

1

TT., trace. 

the broad history of vegetational changes in the coastal 

regions of the Arctic Ocean, paleomagnetic patterns during the time that is indicated by the microtine evolution, 

and the stratigraphic framework provided by oceanic oxygen isotope records provide the constraints for an age interpretation of the Fish Creek Fauna that is very precise 

in comparison with what was possible less than 10 years 

ago. Supportive evidence derives from the ostracode fauna 

at Fish Creek and from temporally and climatically related 

biotas of the Arctic Ocean Borderland. 

0.8 

6.8 

0.4 

5.6 

0.3 

10.7 

0.6 

4.1 

The time of concern is the period between the opening of Bering Strait and the beginning of a Northern 

Hemisphere warm period, about 2.0 Ma ago. Shackleton 

and Opdyke (1977) reported that a progressive cooling 

began about 3.2 Ma ago in the record of the North Pacific 

Ocean, and that the first significant accumulation of continental ice in the Northern Hemisphere peaked about 

2.4 Ma ago. Shackleton and others (1984) reported a 

similar but more detailed record from the North Atlantic. The greater detail of this core (fig. 13) suggests that 

Correlation in the Arctic Ocean Borderland 21 
ALASKA AND GREENLAND 

Modern sea otter, Enhydra 

Microtus from Beringia to Europe 

and North America 

KAP KOBENHAVN FAUNA 

Lepus and Hypolagus 

forest 

r:::.~---1 CAPE DECEIT FAUNA 

Microtus (Lasiopodomys) 

Predicrostonyx hopkinsi 

Phenacomys deeringensis tundra 

Older Cape Deceit section 

alternating forest and tundra 

~":1----1 FISH CREEK FAUNA 

Synaptomys (P/ioctomys) 

Phenacomys gryci 

Enhydriodon 

herb tundra 

Basal Fish Creek section 

Pterygocythereis n. sp. 

shrub tundra, nearby forest 

OCEAN POINT FAUNA 

Enhydriodon 

40% to 60% arboreal pollen 

Bering Strait opens 

Oceanic records indicate that 

continental ice began accumulating 

> 0 

z 

:::> 

(!) 

w 

ID 

Dicrostonyx renidens 

Microtus 

55% arboreal pollen 

-Dicrostonyx renidens 

Microtus (primitive) 

t··J7ea!icrc>stonyx compita/is 

tundra (no forest pollen) 

Predicrostonyx hopkinsi (reworked) 

·-Predicrostonyx, Allophaiomys 

Cromeromys, Lepus 

3% to 6% arboreal pollen 

-rs;yna1ptomys (Plioctomys) 

Mimomys, Cromeromys, Hypo/agus 

15% arboreal pollen decreasing 

to 2% with permafrost in 

youngest beds 

20% arboreal pollen with 

seasonal ice wedges 

Figure 13. Correlation of faunas from Beringian Siberia and Alaska with time (T) in millions of years, paleomagnetic stratigraphy 

(MAG), and the oceanic record of oxygen isotope ratios from North Atlantic site 552A on the Rockall Plateau south of Iceland 

and west of Scotland (Shackleton and others, 1984). All isotopic data on figure from site 552A. Wavy lines in the composite 

Krestovka Section indicate breaks in continuity of sections described by Sher and others (1979). 

this continental ice cap had two major peaks and persisted 

until about 2.0 Ma ago. 

Species of the primitive bog lemming subgenus Synaptomys (Piioctomys) are known from southern Russia, 

Poland, Hungary, Mongolia, northeastern Siberia, 

Alaska, and the Great Plains of North America; their 

evolutionary history is sketched and described in figure 

14. The oldest record is in the Simbugino Fauna from 

southern Russia that is correlated with European faunas 

older than 4 Ma, and comparable faunas in the United 

States are as old as 4.8 Ma (Fejfar and Heinrich, 1983; 

Repenning, 1983b ); the youngest, in the Great Plains of 

the United States, no less than 2.0 Ma old. With the exception of those records from the Great Plains, probably 

all known occurrences should be assigned to S. (P.) mimomiformis Suchov, as there is no known way to diagnose 

them separately. Synaptomys (P.) rinkeri Hibbard and 

Mictomys vetus (Wilson) from 2.6- to 2.0-Ma-old faunas 

of the Great Plains and western mountain States can be 

distinguished from S. (P.) mimomiformis and from 

22 Ancestry of Phenacomys and Arctic Borderland Biota 

younger species that are assigned to more advanced taxa 

(fig. 14). 

The youngest Old World record of Synaptomys (fig. 

13) is from the Kutuyakh Beds of the Krestovka Section 

in the Kolyma Lowlands, Beringian Siberia, where it occurs below and above the 2.5-Ma-old top of the Gauss 

Chron (Sher and others, 1979; Repenning, 1984). This is 

an awkwardly young record, as both the derivative forms, 

S. (P.) rinkeri from the Great Plains west to the Texas 

Panhandle and Mictomys vetus, a North American genus 

derived from Synaptomys (Plioctomys), from west and 

south of the Rocky Mountains, are known from faunas 

slightly older than the end of the Gauss Chron. Obviously, S. (P.) mimomiformis persisted in the Arctic while part 

of its population dispersed southward in North America 

during the climatic deterioration, to evolve into a different 

species of Synaptomys and a different genus, Mictomys, 

by 2.6 Ma ago. Synaptomys (Plioctomys) mimomiformis 

from the Fish Creek Fauna thus suggests an age no 

younger than 2.4 Ma, the earliest part of the Matuyama 
C/) 

>-

::!: 

0 

1-

u 

0 

:J 

a.. 

LEMMINAE 

MICTOMYS 

DIXON 

(2.4 Ma) 

EL CASCO 

(1.6 Ma) 

NEW PARIS 

(0.1 Ma and living) 

CUDAHY 

(0.6 Ma) 

OSZTRAMOS 3 

(3.0 Ma) 

(living) 

DZERAVA SKALA 

(0.1 Ma and living) 

Figure 14. Outline of evolutionary history of brown and bog lemmings, Subfamily Lemminae, shown by changes in pattern 

of chewing surface of first lower molar. Only specimens pertinent to the present discussion are noted here. Synaptomys (P/ioctomys) mimomiformis (labeled Rebielice, from Rebielice Fauna of Poland) has known temporal range from more than 4 Ma ago 

to younger than the 2.5-Ma-old Gauss/Matuyama polarity boundary in Beringian Krestkovka Section, Siberia, and Fish Creek 

Fauna, Alaska. Synaptomys (P/ioctomys) rinkeri (labeled Dixon from the Dixon Fauna, Kansas) and Mictomys vetus (labeled Grand 

View from the Grand View Fauna, Idaho) have evolved out of mimomiformis and are known from deposits in Texas, Arizona, 

and Idaho older than the 2.5-Ma-old Gauss/Matuyama polarity boundary; both grade, in the fossil record, into living forms of 

North America; intermediate forms are shown. 

Although obviously related to Synaptomys and Mictomys, the brown lemming, Lemmus, has its distinctive tooth structure 

already in the oldest known fossils (at least 2 Ma old, as shown by the specimen labeled Osztramos 3, Hungary) and has not 

detectably changed its tooth pattern in living species (shown by latest Pleistocene specimen from Dzerava Skala, Czechoslovakia); 

this genus of Lemminae is not discussed further in present report. 

Chron. Its obvious relict status leaves open the possibility of a still younger age. 

Phenacomys gryci from the Fish Creek Fauna is 

distinctly more primitive than the fossil heather vole Phenacomys deeringensis from the Cape Deceit Fauna (figs. 

5-7). The Fish Creek Fauna might seem to be considerably 

older than the Cape Deceit Fauna on the basis of this 

markedly more primitive evolutionary stage of Phenacomys, and its association with a primitive species of 

Synaptomys, but it is not. The reversed polarity of the 

deposits containing the Fish Creek Fauna, coupled with 

the tundra environment of the fauna and its Pacific 

mollusks, indicates that it cannot be older than the 

beginning of the Matuyama Chron at about 2.5 Ma ago. 

We are therefore forced to choose one of two interpretations: either (1) a very brief period of explosive evolution is 

represented by the dramatic development of Phenacomys 

between the times of Fish Creek and Cape Deceit Faunas 

(the morphologic difference between the two species is far 

greater than that between the Fish Creek species and its 

hypothetical Cromeromys ancestor (>4 Ma), and far 

greater than that between the Cape Deceit species and living species of Phenacomys), or (2) that Phenacomys gryci, 

like Synaptomys (Plioctomys) sp., was a primitive relict 

of the Arctic Ocean Borderland and that the advanced 

P. deeringensis evolved somewhat to the south (but not 

Correlation in the Arctic Ocean Borderland 23 
in conterminous United States) and appeared in the Cape 

Deceit Fauna at the close of the first North American continental glaciation. The first choice provides no more than 

200,000 years for the morphologic change; the second 

could provide as much as 1 million years, and seems more 

realistic. 

The second choice suggests the possibility that the 

Fish Creek microtines, having lived in an arctic refugium, 

could be much younger in age. Although this interpretation enlarges the temporal overlap of ancestral and descendant forms of microtine rodents, that it is actually 

impossible is demonstrated by consideration of climatic 

history and geopolarity. 

According to oceanic oxygen isotope records, the 

first North American continental glaciation appears to 

have terminated 2 Ma ago (fig. 13); this time of climatic 

warming is recognized throughout the Northern 

Hemisphere from the Praetiglian (cold)-Tiglian (warm) 

change in northwestern Europe (Zagwijn and Doppert, 

1978) across Eurasia and North America to northernmost Greenland where evidence indicates that boreal 

forests replaced tundra along its coast close to 2 Ma ago 

(Funder and others, 1985). Within 100,000 years after the 

termination of this first continental glaciation, as 

calibrated by oxygen isotope records, the climatic change 

stimulated the most distinctive of all microtine rodent 

dispersal events in the Northern Hemisphere, which is 

dated in both Europe and North America as having been 

completed during the earliest part of the Olduvai Subchron, about 1.9 Ma ago (Repenning, 1983d). In the 

Krestovka Section of eastern Siberia, Sher and others 

(1979) reported a change in arboreal pollen concentration from 0 to 55 percent at the time of this climatic 

warming (Repenning, 1984). The Fish Creek Fauna does 

not record an increase of arboreal pollen, and its 

paleomagnetic signal cannot represent the reversed 

sediments overlying the 2-Ma-old termination of the 

normal Reunion Subchron. The next similar magnetic 

pattern would be the reversed polarity period following 

the normal Olduvai Subchron, younger than approximately 1.67 Ma; by this time the modern genus of sea 

otter, Enhydra, is known to have evolved (Repenning, 

1983a). 

Age of the Ocean Point Fauna 

The Ocean Point Fauna of the Gubik Formation, 

located about 16 miles (26 km) southeast of the Fish 

Creek Fauna, was discussed by Repenning (1983a). It is 

noteworthy because it was the first evidence in recent 

times that parts of the formation are older than middle 

Pleistocene (older than 1 Ma). In the 1983 discussion 

Repenning concluded that the fauna was older than 

1.5 Ma and younger than 3 Ma on the basis of a primitive 

24 Ancestry of Phenacomys and Arctic Borderland Biota 

form of sea otter and mollusks of North Pacific origin; 

an approximate age of about 2 Ma was discussed. It was 

noted that the pollen flora associated with the marine 

Ocean Point Fauna indicated a nearby forest environment, according to Nelson (1981). 

Since publication of the Ocean Point Fauna (Repenning, 1983a), it has become apparent that just prior to 

2 Ma ago the Arctic Ocean Borderland was not forested. 

The magnetic polarity of the Ocean Point Fauna is normal (JYV. Hillhouse, written commun. to LDC, 1977, and 

Carter and others, in press), and cannot be distinguished 

from either modern or Gauss Chron polarity on declination; in magnetic cleaning (AC) changes in inclination 

were random and showed no tendency toward becoming 

reversed (JYV. Hillhouse, oral commun., 1985). Abundant 

forest pollen and normal polarity could match the Arctic 

Ocean Borderland history during the Olduvai Subchron, 

but this seems too close in time to the earliest known 

record of the modern sea otter, Enhydra. In addition, 

amino acid analyses of marine mollusks show clearly that 

the Ocean Point Fauna is older than the Fish Creek Fauna, 

and these data are supported by geomorphic evidence 

(Carter and others,1986). Because the sediments containing the Fish Creek Fauna formed during the early part 

of the reversed Matuyama Chron, we conclude that the 

Ocean Point marine beds must have formed during some 

part of the normal Gauss Chron (fig. 13). The age estimate 

of the marine Ocean Point Fauna is consequently here 

revised from about 2 Ma to between 3 and 2.5 Ma, and 

is so recognized by Carter and others (1986). 

Age of the Cape Deceit Fauna 

As discussed earlier, the Cape Deceit Fauna appears 

to be very close to 2.1 Ma old (fig. 13). The presence in 

the Cape Deceit Fauna of the primitive meadow mouse 

Microtus (Losiopodomys) deceitensis that is obviously one 

of the first of the Microtus lineage (Repenning, 1983c, 

fig. 2), of the ancient genus of collared lemming 

Predicrostonyx, and of pollen recording a tundra flora 

with a nearby forest in that part of the section underlying the fauna indicates that this age is very close to the 

beginning of the Reunion Normal Subchron. In the 

Krestovka Section, Predicrostonyx is present at an earlier 

time (possibly 200,000 years earlier) than Microtus, and 

the descendant genus Dicrostonyx first appears with the 

oldest Microtus-bearing fauna. This inconsistency seems 

reasonable in view of the Asiatic origin of Dicrostonyx; 

an interpretation on the basis of the synchroneity of 

Predicrostonyx would necessitate the assumption that the 

Microtus lineage originated in North America and dispersed to Eurasia, which is contrary to evidence. Although 

their history is poorly known, the presence of the giant 

pika, Ochotona whartoni (Guthrie and Matthews, 1971), 
in the Cape Deceit Fauna is suggestive of a correlation 

with the Nihowan Fauna of China of this approximate 

age. 

Insofar as we are aware, there is no paleomagnetic 

evidence from the Cape Deceit section. 

Age of the Krestovka Section 

The Krestovka Section at the junction of the 

Krestovka River with the Kolyma River of eastern Siberia 

(figs. 2, 13) has been the object of much study and has 

been described by Sher and others (1979); parts of this 

study have been published separately in other reports by 

Sher, Zazhigin, Virina, Gitterman, and others. As of the 

present date (1986) it is the most detailed record of late 

Pliocene faunal and floral history in the Arctic Ocean 

Borderland. Sher and others (1979, in text on p. 63) inadvertently correlated the youngest of the Kutuyakh Beds 

(containing their Khapry (Pliocene)-equivalent fauna) 

with a time younger than the Olduvai Subchron, thus 

making the Kutuyakh Fauna appear contemporaneous 

with European Biharian faunas (Pleistocene) as used by 

Fejfar and Heinrich (1983). In the immediately preceding 

sentence, however, they correctly suggested that the 

reversely magnetized deposits at the top of the Kutuyakh 

Beds (and overlying the normal deposits they next correlated with the Olduvai) represent the polarity of the early Matuyama Chron. This inconsistency, which makes 

faunas in the younger part of the Krestovka Section appear much younger than they can be, was corrected by 

Repenning (1984), and the faunal succession was correlated with Holarctic history. 

Unlike the North American record in the central 

United States (Easterbrook and Boellstorff, 1984), there 

is no evidence of continental glaciation in Eurasia or in 

Beringia (including Fish Creek) at 2.4 Ma ago (Repenning, 1984), which is the time of the first significant peak 

in o180 of the North Pacific and North Atlantic. Sher 

and others (1979) reported the earliest evidence of permafrost at this time in the youngest part of the Kutuyakh 

Beds of the Krestovka Section in Beringian Siberia. This 

was preceded, in older beds of the Kutuyakh, by a progressive decrease in arboreal pollen for an uncalibrated 

period of the normal magnetism during the Gauss Chron. 

These deposits in the very top of the Kutuyakh Beds, 

recording the earliest reversed magnetism of the 

Matuyama Chron, appear to correlate with the Fish Creek 

Fauna and contain the youngest Old World records of 

Synaptomys (Piioctomys) mimomiformis, the last Beringian record of the ancestral arvicoline microtine 

Mimomys, a relatively primitive form of Cromeromys, 

and the pre-Pleistocene hare Hypolagus (fig. 13). A 

primitive species of Phenacomys may come from this 

fauna. 

Higher in the reversed deposits of the earlier 

Matuyama Chron, the deposits are assigned to the early 

part of the Olyor Suite and contain Predicrostonyx, 

Microtus, and the modern hare Lepus, genera more 

characteristic of the Cape Deceit Fauna, as well as a more 

advanced species of Cromeromys and the earliest 

Allophaiomys and Dicrostonyx. The oldest deposits of 

the Olyor Suite contain a low percentage of arboreal 

pollen (suggesting correlation with the earliest part of the 

Cape Deceit section that contains an alternation of pollen 

assemblages indicative of forest and tundra), but at the 

horizon where Microtus first appears, close to the base 

of the Reunion Subchron, forest elements again have no 

representation in the pollen spectrum. This floral and 

faunal history of the early Olyor Suite appears to be identical with that at Cape Deceit. 

In summary (fig. 13), paleomagnetism, pollen, and 

rapidly evolving mammals all strongly suggest that the 

Cape Deceit Fauna of Alaska correlates best with the 

faunas of the earlier Olyor Suite of the Krestovka Section at the point in time very close to the beginning of 

the Reunion Subchron, about 2.1 Ma ago. These data 

also suggest that the Fish Creek Fauna of Alaska correlates best with the latest part of the Kutuyakh Beds of 

the Krestovka Section at a point in time shortly following the end of the Gauss Chron, about 2.4 Ma ago. The 

marine part of the Gubik Formation at Ocean Point must 

correlate with some part of the older Kutuyakh Beds that 

has greater evidence of forests in the Arctic Ocean 

Borderland and that was deposited during the normal 

Gauss Chron following the opening of Bering Strait 3 Ma 

ago (Gladenkov, 1981). Indeed, Nelson and Carter (1985) 

reported that the arboreal pollen from the marine beds 

at Ocean Point represent as much as 40-60 percent of 

the Tertiary pollen present, a percentage more similar to 

the older Begunov Suite of the Krestovka Section, than 

to the Kutuyakh Beds. 

Age of the Kap Kobenhavn Fauna 

Funder and others (1985) have described a section 

in northernmost Greenland that has deeper water glaciomarine deposits in its lower part, and high-energy 

shoreline deposits in its upper part, indicating little or no 

perennial sea ice. The upper part also contains evidence 

of a forested coast line and is reversely magnetized, except, possibly, at the very top of the magnetic section (fig. 

13). The uppermost part of the section, near the top of 

the paleomagnetic record, contained a few fossil bones 

among which was a large species of the Pliocene rabbit 

Hypolagus, of an age of 2 Ma or older in North America 

and Asia, and (not mentioned by Funder and others) a 

very large species of the modern hare Lepus, of an age 

of 2 Ma or younger in North America. Large Lepus and 

Correlation in the Arctic Ocean Borderland 25 
medium-sized Hypolagus occur together in the Borchers 

Fauna of Kansas in the top of and just above the 2.0 Ma 

"Pearlette Ash" (variously known as the "Pearlette B," 

Borchers, or Huckleberry Ridge ash). In the Krestovka 

Section Lepus first appears earlier, between 2.3 and 

2.4 Ma ago as the records of Sher and others (1979) are 

calibrated by Repenning (1984); Hypolagus is reported 

upsection from Lepus in the Krestovka Section as reworked material, but is not found in fossil faunas believed 

to be in place. 

The combination of (1) a tundra environment in 

northeastern Siberia and Alaska between 2.4 and 2.0 Ma 

ago followed by a forested Arctic Ocean Borderland in 

northeastern Siberia and Greenland at or shortly following 2.0 Ma ago, (2) the reversed polarity of that part of 

the Kap Kobenhavn section recording an open ocean, (3) 

the co-occurence of well known and temporally distinct 

forms of rabbits, and (4) other evidence of age cited by 

Funder and others (1985) leaves little doubt that the Kap 

Kobenhavn section records the time immediately following the culmination of the first continental glaciation of 

North America and of the Praetiglian-Tiglian climatic 

stage boundary of northwestern Europe (fig. 13). 

Environment of the Arctic Ocean Borderland 

Between 3.0 and 1.9 Ma 

Oceanic records of oxygen isotopes indicate that 

about 3.2 Ma ago ice began to accumulate on the continents of the Northern Hemisphere (fig. 13). Although 

not dated, the Begunov Suite of northeastern Siberia may 

possibly represent such an early time and its fossil pollen 

suggests a forested Arctic Ocean Borderland. About 3.0 

Ma ago, North Pacific mollusks reached Iceland, indicating that the Bering Strait had opened and connected 

the North Pacific with the Arctic Ocean. The marine beds 

at Ocean Point, Alaska, were deposited sometime between the opening of the strait and about 2.5 Ma ago; 

they indicate a forested borderland and an ice-free Arctic 

Ocean. The Ocean Point deposits would seem to have 

been deposited earlier in the 3.0 to 2.5 Ma time interval 

than the basal beds of the Fish Creek section because the 

basal Fish Creek beds, with their warm-water ostracode 

assemblage, appear to be about 2.5 Ma old on paleomagnetic grounds. 

The Fish Creek section records a transition from 

shrub tundra to herb tundra through a stratigraphic sequence that is reversely magnetized, but the Arctic Ocean 

was not frozen at the time. The section appears to correlate with the uppermost part of the Kutuyakh Beds of 

northeastern Siberia which have the same magnetic pattern, the same floral pattern, and very similar mammalian 

species; these Kutuyakh Beds record the first permafrost 

and first full tundra of northeastern Siberia. The Fish 

26 Ancestry of Phenacomys and Arctic Borderland Biota 

Creek Fauna, in the upper part of the Fish Creek section, indicates a cooler, but not frozen, Arctic Ocean. 

This fauna is believed to be 2.4 Ma old and to have been 

deposited during the beginning of the first North American continental glaciation, a glaciation that extended 

southward in North America to Iowa. Rea and Schrader 

(1985) discussed evidence from the North Pacific indicating that significant ice rafting began at this time. 

Shackleton and others ( 1984) indicated a similar event in 

the North Atlantic at the same time. Despite these indications of extensive ice accumulation, all available evidence 

in the Fish Creek Fauna indicates that the Arctic Ocean 

was not yet frozen. 

Following deposition of the Fish Creek Fauna and 

during the first glaciation of North America, the Arctic 

Ocean Borderland may have alternated between supporting tundra or boreal forest during the time between 2.4 

and 2.0 Ma. This span of time appears in the oceanic 

records as several peaks in the accumulation of continental ice and appears to be represented in the section 

underlying the Cape Deceit Fauna of the Seward Peninsula; it is expressed there as alternating forest and tundra pollen records. A similar record is suggested by minor 

increases in arboreal pollen in the basal part of the Olyor 

Suite of the Krestovka Section in Siberia. The Cape Deceit 

Fauna, in the upper part of the Seward Peninsula section, is associated with tundra and appears to correlate 

with faunas in the Olyor Suite having no arboreal pollen 

at the horizon of the Reunion Subchron, about 2.1 Ma 

ago. It also appears to correlate with the last peak of the 

first continental glaciation as indicated in the oceanic 

record. 

The north Greenland locality at Kap Kobenhavn 

records evidence indicating that the Arctic Ocean was not 

frozen and that forests returned to its borderland about 

2 Ma ago. This warm period continued (1) at least to the 

end of the Olduvai Subchron [Zagwijn and Doppert 

(1978) believed that the Tiglian warm period ended and 

the Eburonian cold period started at that time], or (2) 

to shortly following the Olduvai [Herman and Hopkins 

(1980) reported that ice rafting increased in the Arctic 

Ocean at that time, if the normal event they call the Gauss 

Chron is considered the Olduvai Subchron], or (3) to 

about 1.4 Ma when Pacific Core V28-239 shows an 

abrupt shortening of isotope "warm" periods. 

At present, the evidence of Herman and Hopkins 

(1980), which suggests that the Arctic Ocean froze about 

850,000 years ago (with the above-mentioned revision of 

magnetic correlations), appears to be the earliest evidence 

of a frozen Arctic Ocean. This date corresponds to the 

beginning of oxygen stage 22, to a major Holarctic dispersal of microtine rodents that is rather well dated in both 

Europe and North America, and to the first advance of 

the Nebraskan ice sheets southward into the midwestern 

United States (Easterbrook and Boellstorff, 1984). 
REFERENCES CITED 

Birks, H.J.B., 1973, Modern pollen rain studies in some arctic 

and alpine environments, in Birks, H.J.B., and West, R.G., 

eds., Quaternary plant ecology: New York, John Wiley, 

p. 143-168. 

Brouwers, Elisabeth, Marincovich, Louie, Jr., and Hopkins, 

D.M., 1984, Paleoenvironmental record of Pleistocene transgressive events preserved at Skull Cliff, northern Alaska, 

in Reed, K.M., and Bartsch-Winkler, Susan, eds., The 

United States Geological Survey in Alaska-Accomplishments during 1982: U.S. Geological Survey Circular 939, 

p. 9-11. 

Carter, L.D., and Brigham-Grette, Julie, in press, Late Cenozoic 

marine transgressions of the Alaska Arctic Coastal Plain: 

Geological Survey of Canada Publication. 

Carter, L.D., Brigham-Grette, Julie, Marincovich, Louie, Jr., 

Pease, V.L., and Hillhouse, J.W., 1986, Late Cenozoic Arctic Ocean sea ice and terrestrial paleoclimate: Geology, 

v. 14, p. 675-678. 

Carter, L.D., and Galloway, J.P., 1985, Engineering geologic 

maps of northern Alaska, Harrison Bay Quadrangle: U.S. 

Geological Survey Open-File Report 85-256, 49 p. 

Carter, L.D., Marincovich, Louie, Jr., Brouwers, E.M., and 

Forester, R.M., 1979, Paleogeography of a Pleistocene 

coastline, Alaskan Arctic Coastal Plain, in Johnson, K.M., 

and Williams, J.R., eds., The United States Geological 

Survey in Alaska-Accomplishments during 1978: U.S. 

Geological Survey Circular 804-B, p. B39-B4l. 

Chaline, Jean, 1975, Taxonomie des Campagnols (Arvicolidae, 

Rodentia) de Ia sous-famille Dolomyinae nov. dans 

!'hemisphere Nord: Comptes Rendus Hebdomadaires des 

Seances de l'Academie des Sciences, Serie D, v. 281, 

p. 115-118. 

Easterbrook, D.J., and Boellstorff, John, 1984, Paleomagnetism 

and chronology of early Pleistocene tills in the central 

United States, in Mahaney, W.C., ed., Correlation of 

Quaternary chronologies: Norwich, England, Geo Books, 

p. 73-101. 

Erbaeva, M.A., 1976, The origin, evolution, and intraspecific 

variability of Brandt's vole from the Anthropogene of 

western Transbaikalia, in Gromov, I.M., ed., Rodent evolution and history of their Recent fauna: Academy of Sciences 

of the U.S.S.R., Proceedings of the Zoological Institute, v. 

66, p. 102-116. [In Russian.] 

Eshelman, R.E., 1975, Geology and paleontology of the early 

Pleistocene (late Blancan) White Rock Fauna from northcentral Kansas: University of Michigan Museum of Paleontology, Paper 13, 60 p. 

Fejfar, Oldrich, and Heinrich, Wolf-Dieter, 1983, ArvicolidenSukzession und Biostratigraphie des Oberpliozans und 

Quartars in Europa: Schriftenreihe fur geologische Wissenschaften, Berlin, 19/20, p. 61-109. 

Foster, N.R., 1981, A synopsis of the marine prosobranch 

gastropod and bivalve mollusks in Alaskan waters: University of Alaska, Institute of Marine Science, Report R81-3, 

479 p. 

Funder, Svend, Abrahamsen, Niels, Bennike, Ole, and FeylingHanssen, RW., 1985, Forested arctic-Evidence from North 

Greenland: Geology, v. 13, p. 542-546. 

Gladenkov, Y.B., 1981, Marine Plio-Pleistocene of Iceland and 

problems of its correlation: Quaternary Research, v. 15, 

p. 18-23. 

Gromov, I.M., and Polyakov, I.Yu., 1977, Polevki (Microtinae)-

Mammals, Part Ill, in Fauna of the U.S.S.R.: Academy of 

Science U.S.S.R., Zoologie Institute, New Series No. 116, 

No. 8, 504 p. [In Russian.] 

Guthrie, R.D., and Matthews, JY., 1971, The Cape Deceit 

Fauna-early Pleistocene mammalian assemblage from the 

Alaskan Arctic: Quaternary Research, v. 1, p. 474-510. 

Hazel, J.E., 1967, Classification and distribution of the Recent 

Hemicytheridae and Trachyleberididae (Ostracoda) off 

northeastern North America: U.S. Geological Survey Professional Paper 564, p. 1-49. 

___ 1970, Atlantic continental shelf and slope of the United 

States-ostracode zoogeography in the southern Nova Scotian and northern Virginian faunal provinces: U.S. 

Geological Survey Professional Paper 529-E, p. E1-E21. 

Herman, Yvonne, and Hopkins, D.M., 1980, Arctic oceanic 

climate in late Cenozoic time: Science, v. 209, p. 557-562. 

Hopkins, D.M., 1967, Quaternary marine transgressions in 

Alaska, in Hopkins, D.M., ed., The Bering land bridge: 

Stanford, Calif., Stanford University Press, p. 47-90. 

Hulten, Eric, 1968, Flora of Alaska and neighboring territories: 

Stanford, Calif., Stanford University Press, 1008 p. 

Johnson, M.L., 1973, Characters of the heather vole, Phenacomys, and the red tree vole, Arborimus: Journal of Mammalogy, v. 54, p. 239-244. 

von Koenigswald, Wighart, and Martin, L.D., 1984, Revision 

of the fossil and Recent Lemminae (Rodentia: Mammalia): 

Carnegie Museum of Natural History Special Publication 

9, p. 122-137. 

Kowalski, Kazimerz, 1977, Fossil lemmings (Mammalia: Rodentia) from the Pliocene and early Pleistocene of Poland: Acta 

Zoologica Cracoviensia, v. 22, p. 297-317. 

Livingstone, D.A., 1955, Some pollen profiles from arctic Alaska: 

Ecology, v. 36, p. 587-600. 

Maser, Chris, Mate, B.R., Franklin, J.F., and Dyrness, C.T., 1981, 

Natural history of Oregon coast mammals: U.S. Forest Service and Bureau of Land Management General Technical 

Report PNW-133, 496 p. 

Matthews, JY., Jr., 1974, Quaternary environments at Cape 

Deceit (Seward Peninsula, Alaska)-Evolution of a tundra 

ecosystem: Geological Society of America Bulletin, v. 85, 

p. 1353-1384. 

Moriya, K., 1978, Flora and palynomorphs of Alaska: Tokyo, 

Kodansha Publishing Co., 367 p. [In Japanese.] 

Neale, JW., and Howe, HY., 1975, The marine Ostracoda of 

Russian Harbour, Novaya Zemlya and other high latitude 

faunas: Bulletins of American Paleontology, v. 65, 

p. 381-432. 

Nelson, R.E., 1979, Quaternary environments of the arctic slope 

of Alaska: Seattle, Wash., University of Washington M.Sc. 

thesis, 141 p. 

___ 1981, Paleoenvironments during deposition of a section 

of the Gubik Formation exposed along the lower Colville 

River, North Slope, in Albert, N.R.D., and Hudson, T., eds., 

The United States Geological Survey in AlaskaAccomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B9-B11. 

References Cited 27 
Nelson, R.E., and Carter, L.D., 1985, Pollen analysis of a late 

Pliocene and early Pleistocene section from the Gubik Formation of Arctic Alaska: Quaternary Research, v. 24, 

p. 295-306. 

Rea, D.K., and Schrader, Hans, 1985, Late Pliocene onset of 

glaciation-ice rafting and diatom stratigraphy of North 

Pacific DSDP cores: Palaeogeography, Palaeoclimatology, 

Palaeoecology, v. 49, p. 313-325. 

Repenning, C.A., 1976, Enhydra and Enhydriodon from the 

Pacific coast of North America: U.S. Geological Survey 

Journal of Research, v. 4, p. 305-315. 

___ 1983a, New evidence for the age of the Gubik Formation, Alaskan North Slope: Quaternary Research, v. 19, 

p. 356-372. 

___ 1983b, Faunal exchanges between Siberia and North 

America: Schriftenreihe fur geologische Wissenschaften, 

Berlin, 19/20, p. 333-346. 

___ 1983c, Pitmys meadensis Hibbard from the Valley of 

Mexico and the classification of North American species 

of Pitmys (Rodentia: Cricetidae): Journal of Vertebrate 

Paleontology, v. 2, p. 471-482. 

___ 1983d, Evidence for earlier date of Ubeidiya, Israel 

hominid site-Repenning replies: Nature, v. 304, p. 

375-376. 

___ 1984, Quaternary rodent biochronology and its correlation with climatic and magnetic stratigraphies, in Mahaney, 

W.C., ed., Correlation of Quaternary chronologies: Norwich, England, Geo Books, p. 105-110. 

Shackleton, N.J., and Opdyke, N.D., 1977, Oxygen-isotope and 

paleomagnetic evidence for early northern hemisphere 

glaciation: Nature, v. 270, p. 216-219. 

Shackleton, N.J., Backman, J., Zimmerman, H., Kent, D.V., 

Hall, M.A., Roberts, D.O., Schnitker, D., Baldauf, J.G., 

Desprairies, A., Homrighausen, R., Huddlestun, Paul, 

Keene, J.B., Kaltenback, A.J., Krumsiek, K.A.O., Morton, A.C., Murray, J.W., and Westberg-Smith, J., 1984, 

28 Ancestry of Phenacomys and Arctic Borderland Biota 

Oxygen isotope calibration of the onset of ice-rafting and 

history of glaciation in the North Atlantic region: Nature, 

v. 307, p. 620-623. 

Sher, A.V., Gitterman, R.Ye., Zazhigin, V.S., and Kiselyov, 

S.V., 1977, New data on the late Cenozoic deposits of the 

Kolyma lowland: Academy of Sciences of the U.S.S.R., 

Isvestiya, Series Geologie, 1977, p. 69-83. [In Russian.] 

Sher, A.V., Kaplina, T.N., Kouznetsov, Yu.V., Virina, E.I., 

and Zazhigin, V.S., 1979, Late Cenozoic of the Kolyma 

Lowland: XIV Pacific Science Congress, Tour Guide XI, 

Academy of Sciences of the U.S.S.R., Moscow, 115 p. 

Sher, A.V., Virina, Ye.l., and Zazhigin, V.S., 1977, The 

stratigraphy, paleomagnetism, and mammalian fauna of 

the Pliocene and lower Quaternary deposits around the 

lower reaches of the Kolyma River: Doklady, Earth Science 

Section, v. 234, p. 123-126. [Translation from Russian.] 

Suchov, V.P., 1976, Remains of lemmings in the Bashkirian 

Pliocene deposits: Academy of Sciences of the U.S.S.R., 

Proceedings of the Zoological Institute, v. 66, p. 117-121. 

[In Russian.] 

Swain, F.M., 1963, Pleistocene Ostracoda from the Gubik Formation, Arctic Coastal Plain, Alaska: Journal of Paleontology, v. 37, p. 798-834. 

Vangengeim, E.A., and Sher, A.V., 1970, Siberian equivalents 

of the Tiraspol faunal complex: Palaeogeography, 

Palaeoclimatology, Palaeoecology, v. 8, p. 197-207. 

Viereck, L.A., and Little, E.L., 1972, Alaska trees and shrubs: 

U. S. Department of Agriculture Forest Service Handbook 

4_10, 265 p. 

Zagwijn, W.H., and Doppert, J.W., 1978, Upper Cenozoic of 

the southern North Sea Basin-paleoclimatic and 

paleogeographic evolution: Geologie en Mijnbouw, v. 57, 

p. 577-588. 

Zazhigin, V.S., 1980, Late Pliocene and Anthropogene rodents 

of the south of Western Siberia: Academy of Sciences of 

the U.S.S.R., Transactions, v. 339, 159 p. [In Russian.] 
INDEX 

[Italic page numbers indicate major references] 

A 

Abies ............................................................................. 19 

spp ............................................................................ 19 

Admete regina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Aforia circinata .. ....... ...... .................... ......... ... .............. .. 15 

Age of the Cape Deceit Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Fish Creek Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Kap Kobenhavn Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Krestovka Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Ocean Point Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Alaska panhandle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

albipes, Phenacomys ........................................................... 4 

Allophaiomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 25 

alpina, Ochotona . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

americana, Pterygocythereis . ... ..... ... ... ...... ... ... ................. .... 14 

Anchorage pollen flora . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Anvilian time . .. . . . .. . . . .. . .. . . . . . . . . . . . . . .. . . .. . . .. . .. . . .. . . . .. . .. . ... . .. . .. . . 11 

Arborimys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

longicaudus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Arctic Foothills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

arctic refugium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

arctica, Hiatella . .. .. . .. . . .. . . .. . .. . . . .. . .. . .. . ... . . .. . . ... ... . .. . .. . . .. . .. . .. 16 

Artemisia ........................................................................ 20 

Arvicola . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Arvicola-Allophaiomys group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Arvicolinae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

arvicoline rodents ........................................................... 4, 8 

Astarte borealis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Axinopsida orbiculata ................................................... 15, 17 

B 

banksiana, Pinus . .. ... ...... .. ...... .. ... ... ... ......... ............. .... ... .. 19 

Barter Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Bering Sea ... ... .......... .......................... ............ ... .... ........ 15 

Bering Strait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 , 14 

opening of ........................................................ 21, 25, 26 

Beringia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 , 4 

Beringian Faunal Province ................................................... 5 

Beringian Siberia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Beringian time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

beringiana, Neptunea .. ........... ... ............ ... ......... ... ............. 15 

Betula ............................................................................ 19 

Biharian faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Blancan V faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Borchers ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Borchers Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

borealis, Astarte . . .. . . . . . . .. . .. . . . . . . . . . . . . . . .. . . .. . .. . .. . . . . .. . .. . . . . . .. . . . . . 16 

Boreotrophon pacificus ...................................................... 16 

bradii, Sarsicytheridea ...................................................... pl.1 

Brooks Range ............................................................ 19, 20 

c 

californiense, Clinocardium ................................................ 15 

Canada ...................................................................... 4, 19 

Canadian life zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Cape Deceit Fauna ............................................. 4, 5, 23, 26 

age ............................................................................ 24 

Caryophyllaceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Chukchi Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

circinata, Aforia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Clinocardium californiense .............. ............ .......... .......... ... 15 

Colville River . .. . . . .. . .. . . . . . . .. ... .. . .. . .. . . . . .. . .. . . . . ... . .. . . . .. . . . .. . . 1, 13 

contorta, Pinus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

cooperi, Synaptomys (Synaptomys) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Correlation in the Arctic Ocean Borderland . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Cosomys ........................................................................... 8 

(Cosomys) sawrockensis, Mimomys ........................................ 9 

Cromerian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Cromeromys ........................................................... 7, 23, 25 

intermedius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

irtyshensis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Cyclogyra involvens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Cyperaceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19, 20 

Cytheretta teshekpukensis ............................................ 14; pl.l 

Cytherissa lacustris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Cytheropteron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

pyramidale .................................................................. pl. 1 

D,E 

deceitensis, Lasiopodomys .................................................... 5 

Microtus (Lasiopodomys) ................................................. 24 

deeringensis, Phenacomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 7, 23 

Dicrostonyx ............................................................ 6, 24, 25 

East Anglia, Norwich Crag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Echinocythereis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Elphidiella groenlandica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Enhydra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 24 

lutris ............................................................................ 3 

Enhydriodon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

reevei ........................................................................... 3 

Ericaceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

europaeus, Synaptomys (Plioctomys) ....................................... 4 

F-H 

First finds of Fish Creek bones and teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Fish Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 11 

Fauna ..................................................................... 1, 11 

age ......................................................................... 20 

Fish Creek section, and environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

flora . . . . .. .. .. . .. . .. . . . . . . .. . . . .. . .. ... . .. . . . . . . .. . .. . .. . . .. . .. . . . .. .. . .. . .. . .. 18 

Flora of the Fish Creek section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Index 29 
Gauss Chron ........................................................ 22, 24, 25 

Gauss-Matuyama boundary ................................................. 11 

glauca, Pice a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Gramineae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Great Plains, North America .......................................... 4, 22 

groenlandica, Elphidiella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

groenlandicus, Serripes ... . . ... ... .. . .. ... ... .. . . . ... ... ... .. .. .. . ... ... ... .. 16 

gryci, Phenacomys .................................................. 6, 11, 23 

Gubik Formation ....................................... 1, 3, 6, 13, 15, 24 

Gulf of Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Harrison Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6, 11 

Heterocyprideis sorbyana ................................................ pl. 1 

Hiatella arctica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . 16 

Holocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6, 14 

hopkinsi, Predicrostonyx ...................................................... 5 

Huckleberry Ridge ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Hudsonian life zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Hypolagus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

1-K 

inexpectata, Pterygocythereis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

intermedius, Cromeromys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Mimomys ....................................................................... 7 

Phenacomys ............................................................... 4, 7 

involvens, Cyclogyra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

irtyshensis, Cromeromys ...................................................... 7 

Juneau ........................................................................... 19 

Kap Kobenhavn Fauna, age ............................................... 25 

Kazakh S.S.R. . ................................................................. 7 

Kolyma Lowlands ........................................................ 6, 22 

Kolyma River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Kotzebuan time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

Krestovka River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6, 25 

Krestovka Section ................................................... 5, 22, 24 

age ............................................................................ 25 

kroyeri, Plicifusus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Kutuyakh Beds ................................................. 6, 22, 25, 26 

Kutuyakh Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

L 

lacustris, Cytherissa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

laricina, Larix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Larix ......................................................................... 3, 19 

laricina . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Lasiopodomys deceitensis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

prebraebranti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

(Lasiopodomys) deceitensis, Microtus .................................... 24 

Late Cretaceous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

leffingwelli, Neptunea lyrata . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. . .. 15 

Lepus ............................................................................ 25 

Liomesus ooides ... ... .. ... .. ..... ... .. . ... .. ... ... ... ... ... .. . ... .... ... .. ... . 15 

Littorina squalida . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

longicaudus, Arborimys ....................................................... 4 

Phenacomys ............................................................... 4, 7 

Loxoconcha venepidermoidea ................................. 11, 14; pl.l 

lutris, Enhydra .................................................................. 3 

lyrata leffingwelli, Neptunea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 15 

M 

Mackenzie Delta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Mammals of the Fish Creek Fauna ....................................... 3 

Manning Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

30 Ancestry of Phenacomys and Arctic Borderland Biota 

mariana, Picea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Marsh anticline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Matuyama Chron .................................................. 22, 24, 25 

mcknighti, Mimomys (Ophiomys) ........................................... 9 

microtine rodents .................................... 2, 8, 14, 20, 24, 26 

Microtus ................................................................ 5, 24, 25 

(Lasiopodomys) deceitensis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Mictomys ........................................................................ 22 

vetus .......................................................................... 22 

Miluveach River ............................................................. pl.1 

mimomiformis, Synaptomys (Plioctomys) ....................... 4, 22, 25 

Mimomys ............................................................ 5, 7, 8, 25 

(Cosomys) sawrockensis .................................................... 9 

(Ophiomys) mcknighti ....................................................... 9 

intermedius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

savini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7, 11 

Mimomys Kante .................................................... 4, 6, 7, 8 

Miocene ......................................................................... 11 

mirabilis, Rabilimis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. 11; pl.l 

Mollusks of the Fish Creek Fauna . ... ... ... . .. ... . .. ... .. .. . .... ... ... . 14 

Mya truncata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

N,O 

Nebraskan ice sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Neptunea beringiana . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

lyrata leffingwelli . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 15 

Nihowan Fauna, China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

North Pacific Ocean ......................................................... 21 

North Slope ............................................................... 11, 19 

Northern Hemisphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

Northwest Territories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Norton Sound ... .. .. .. . . .. ... .. ... .. ... .. ... .. . . .. ... ... ... ... .. ... . ... ... ... .. 14 

Norwegian Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Norwich Crag, East Anglia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Nuphar .......................................................................... 20 

Nuwok Member, Sagavanirktok Formation ............................. 11 

Ocean Point ........................................................... 3, 13, 19 

Ocean Point Fauna, age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

oceanic oxygen isotope records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Ochotona .......................................................................... 3 

alpina ........................................................................... 3 

whartoni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Ogmodontomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Olduvai Subchron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24, 25 

Olyor Suite ................................................................ 25, 26 

ooides, Liomesus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Ophiomys ......................................................................... 8 

(Ophiomys) mcknighti, Mimomys ........................................... 9 

orbiculata, Axinopsida .................................................. 15, 17 

Ostracodes of the Fish Creek section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

p 

pacificus, Boreotrophon . .. . ... .. . .. .. . .. .. . .. . ... . .. . .. . . .. . ... ... .... ... ... 16 

Paleocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Paleovegetation interpretations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Paracyprideis pseudopunctillata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

paramirabilis, Rabilimis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11; pl.l 

"Pearlette Ash" ................................................................ 26 

"Pearlette B" ash ............................................................. 26 

Phenacomys ........................................ 2, 4, 7, 8, 20, 23, 25 

albipes .......................................................................... 4 

deeringensis ......................................................... 4, 7, 23 

gryci ................................................................. 6, 11, 23 

intermedius ................................................................ 4, 7 
longicaudus ................................................................ 4, 7 

sp ................................................................................ 6 

Picea ............................................................................. 19 

glauca ........................................................................ 19 

mariana ...................................................................... 19 

Pinus . . .. ... .. . .. .. .. . ... .. ... ... ... .. ... .. . .. ... ... ... ... ... ... ... ... ... .... ... .. 19 

banksiana . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

contorta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Pleistocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 , 24 

Plicifusus kroyeri . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . .. . .. . . . . . . . . . . . . . .. . . . . . .. 16 

Pliocene ...................................................... 1, 6, 11, 20, 25 

(Plioctomys), Synaptomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

europaeus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

mimomiformis ...................................................... 4, 22, 25 

rinkeri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 22 

sp ................................................................................ 4 

Pliomys ............................................................................ 4 

Pliophenacomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Praetiglian-Tiglian climatic stage boundary ........................ 24, 26 

prebraebranti, Lasiopodomys ................................................. 5 

Predicrostonyx ........................................................ 6, 24, 25 

hopkinsi ........................................................................ 5 

Prudhoe Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pl. 1 

pseudopunctillata, Paracyprideis . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . 11 

Pterygocythereis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

americana .. .. ... .. .. ... . . . ... .. ... .. . .. . .. ... ... .. . .. . ... ... ... ... ... . ... ... . 14 

inexpectata . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . .. . . . . 14 

n.sp .................................................................... 11; pl.1 

pyramidale, Cytheropteron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pl.1 

R 

Rabilimis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

mirabilis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11; pl. 1 

paramirabilis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11; pl. 1 

septentrionalis . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 14; pl.l 

reevei, Enhydriodon ............................................................ 3 

regina, Admete .. . . . .. . .. .. .. . . .. . . . .. ... .. ... ... .. . ... ... .... .. .. . .... .. . . ... . 15 

Retusa umbilicata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

Reunion Normal Subchron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Reunion Subchron ................................................... 5, 24, 25 

{{U.S. GOVERNMENT PRINTING OFFICE: 1987-773-047/46,049 REGION NO.8 

rinkeri, Synaptomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

(Plioctomys) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 22 

Robertsonites tuberculata .................................................. p1.1 

s 

Sagavanirktok Formation, Nuwok Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Salix ............................................................................. 20 

Sarsicytheridea bradii ....................................................... pl.1 

savini, Mimomys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7, 11 

sawrockensis, Mimomys (Cosomys) . . . . . . . . . . . .. . .. . . . . . . . . . . .. . .. . . . . . . . 9 

septentrionalis, Rabilimis . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 14; pl.l 

Serripes groenlandicus .. .. . ... ... .. ... ...... .. ... ... .... .. . ... ... ... ... ... ... 16 

Seward Peninsula ......................................................... 4, 15 

Simbugino Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

sorbyana, Heterocyprideis ................................................. p1.1 

Spermophilus undulatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

squalida, Littorina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Synaptomys ............................................................ 4, 20, 22 

rinkeri .......................................................................... 4 

(Plioctomys) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

europaeus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

mimomiformis ................................................... 4, 22, 25 

rinkeri ................................................................. 4, 22 

sp ............................................................................. 4 

(Synaptomys) cooperi ....................................................... 4 

(Synaptomys) cooperi. Synaptomys ......................................... 4 

T-Z 

teshekpukensis, Cytheretta ........................................... 14; pl.l 

truncata, Mya . ...... .. ... . .... .. ... ... ... ... ... . .. . . ... ....... ... ... ....... .. . 16 

tuberculata, Robertsonites ................................................. p1.1 

Tubuliflorae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

umbilicata, Retusa . ..... .. ... ... ... .. . . . ... ... .. ... ... .... ... ... .... .. ... ... .. 17 

undulatus, Spermophilus ...................................................... 3 

Valeriana ....................................................................... 20 

venepidern:widea, Loxoconcha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 14; pl.l 

vetus, Mictomys ............................................................... 22 

whartoni, Ochotona .......................................................... 24 

Yukon River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Yukon Territory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Index 31 

PLATE 1 

Contact photographs of the plate in this report are available, 

at cost, from U.S. Geological Survey Library, 

Federal Center, Denver, CO 80225 
PLATE 1 

[Bar scale = 100 micrometers] 

Scanning electron micrographs of the diagnostic ostracode species from the Fish Creek section. Stratigraphic positions of localities 

are shown on figure 3 except for 83-EB-187, which is from Miluveach River, and HLA-12, which is from a borehole taken in 

the inner shelf off Prudhoe Bay. 

Figure 1. Pterygocythereis n. sp. Exterior of left valve, female. Locality 83-EB-187A. 

2. Rabilimis paramirabilis (Swain, 1963). Exterior of left valve, male. Locality 83-EB-187A. 

3. Rabilimis septentriona/is (Brady, 1866). Exterior of left valve, male. Locality 83-EB-187. 

4. Rabilimis mirabilis (Brady, 1868). Exterior of left valve, male. Locality HLA-12, 27.5-28.0 ft. 

5. Robertsonites tuberculata (Sars, 1865). Exterior of left valve, juvenile. Locality 83-EB-183. 

6. Cytheretta teshekpukensis Swain, 1963. Exterior of right valve, male. Locality 83-EB-183. 

7. Loxoconcha venepidermoidea Swain, 1963. Exterior of left valve. Locality 83-EB-183. 

8. Heterocyprideis sorbyana (Jones, 1856). Exterior of left valve, male. Locality 83-EB-183. 

9. Sarsicytheridea bradii (Norman, 1865). Exterior of right valve, male. Locality 83-EB-178. 

10. Cytheropteron pyramidale of Neale and Howe, 1975. Exterior of left valve. Locality 83-EB-181. 
U.S. GEOLOGICAL SURVEY BULLETIN 1687 PLATE 1 

PTERYGOCYTHEREIS, RABILIMIS, ROBERTSONITES, CYTHERETI'A, LOXOCONCHA, 

HETEROCYPRIDEIS, SARSICYTHERIDEA, AND CYTHEROPTERON