ROBERT E. MART Cranial and Bacular

' Variation in Populations

of Spiny Rats of the

Genus Proechimys

(Rodentia: Echimyidae) *

mm South America

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • 1970 NUMBER35
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SMITHSONIAN CONTRIBUTIONS TO

ZOOLOGY

NUMBER 35

Robert E. Martin Cranial and Bacular

Variation in Populations

of Spiny Rats of the

Genus Proechimys

(Rodentia: Echimyidae)

from South America

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

I97O
ABSTRACT

Martin, Robert E. Cranial and Bacular Variation in Populations of Spiny Rats

of the Genus Proechimys (Rodentia: Echimyidae) from South America. Smithsonian

Contributions to Zoology, 35:1-19. 1970.—Specimens of Proechimys from 12 localities in Bolivia, Brazil, Colombia, and Peru, were studied to assess the degree of

variation in bacular, cranial, and dental morphology, and pelage. Coefficients of

variation and Student's t values were computed for selected cranial measurements to

evaluate intra- and interpopulation variation. Studies on tooth wear demonstrated

considerable variation in dental occlusal pattern and suggested that taxonomic

assignment based entirely on dental morphology may be misleading. Descriptions and

illustrations of bacula from most localities indicate that these bones are highly variable

in overall dimensions, but have common structural features at a particular locality.

Most specimens are tentatively referred to Proechimys guyannensis, although P. canicolUs, P. quadruplicates, and P. steerei were also represented. Proechimys guyannensis

is regarded as a highly variable species. It is suggested that subspecific delimitation

may not adequately express the variation observable in this species.

Official publication date is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year.

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Robert E. Martin Cranial and Bacular

Variation in Populations

of Spiny Rats of the

Genus Proechimys

(Rodentia: Echimyidae)

from South America

Introduction

Spiny rats of the genus Proechimys are caviomorph

rodents of the family Echimyidae inhabiting most

forested areas of South America north of the Tropic

of Capricorn and Central America northward to Nicaragua (Moojen, 1948). Although these rats frequently

live near streams, they are not entirely riparian and

may inhabit semiarid grasslands (Hershkovitz, 1948)

or dry forests (Allen, 1904).

The wide range of morphological variation observed

in these rats has made species determination difficult.

This has caused problems in the taxonomy of the genus

(see Thomas, 1927, 1928a, 1928b; Hershkovitz, 1948;

and Moojen, 1948). Thomas (1928a, p. 262) remarked that "The bewildering instability of the characters of these spiny rats makes it at present impossible to sort them according to locality into separate

species, subspecies, or local races."

The present study is an effort to measure some elements of variation in Proechimys, and thereby provide

an aid toward future taxonomic work in the genus.

Initially, the most useful measurements were selected

by a study of variation within a population. The primary aims were to: (1) assess interpopulation variation in cranial dimensions; and (2) attempt to corMartin, Robert E., Department of Biology, Texas Tech

University, Lubbock, Texas 79409.

relate these data with the results of analyses of cranial,

bacular, dental, and pelage morphology. Taxonomic

assignment was only a secondary objective. Descriptions were written of the morphological features common to specimens from each locality, and comparisons made with other populations. The accounts

reflect differences between populations from different

localities, and offer suggestions on taxonomic assignment, but are not taxonomic descriptions in the strict

sense. All specimens examined are deposited in the

mammal collection of the National Museum of Natural History.

I wish to express my sincere appreciation to the individuals who aided in the completion of this report.

Dr. Gary L. Ranck, formerly Curator of the Mammal

Identification Service, Smithsonian Institution, directed the study and offered helpful advice and criticism. Dr. Henry W. Setzer, Associate Curator, Division

of Mammals, Smithsonian Institution, aided in the

statistical treatment of the data. Dr. Ronald H. Pine,

Curator, Mammal Identification Service, reviewed the

manuscript and sent specimens for additional study.

Dr. Charles O. Handley, Jr., Curator-in-Charge, and

Dr. David H. Johnson, Research Curator, Division of

Mammals, gave useful advice. Dr. George E. Watson,

Chairman, and other personnel of the Department of

Vertebrate Zoology, Smithsonian Institution, provided

helpful comments on the manuscript. Dr. Merle L.

1
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Kuns and associates of the Middle America Research

Unit collected most of the specimens analyzed.

At Oklahoma State University, Dr. Bryan P. Glass,

Professor of Zoology, served as major advisor and

critically read the manuscript. Dr. Herbert L. Bruneau, Associate Professor of Zoology, and Dr. William A. Drew, Associate Professor of Entomology,

served on the graduate advisory committee and read

the manuscript. Dr. George A. Moore, Professor

Emeritus of Zoology, gave advice and critically read

the manuscript. At Texas Tech University Dr.

Robert L. Packard, Professor of Biology, and Mr.

Tony R. Mollhagen, provided helpful advice on the

manuscript.

Mr. Paul Ryan took the photographs that aided in

the preparation of Figure 3. My wife, Patricia, helped

by recording data and preparing most of the illustrations. Mrs. Frank Roberts and Mrs. Daniel Carabine

typed final stages of the manuscript.

This report is based on a research project conducted in 1967 while the author was a summer

research assistant in the Division of Mammals, Smithsonian Institution, Washington, D.C. Financial aid

during this period was provided by a stipend from the

Office of Education and Training, Smithsonian Institution. The paper that resulted from that study was

submitted to the Graduate College of Oklahoma State

University in partial fulfillment of the requirements for

the degree of Master of Science in Zoology.

Phytogeny and Nomenclature

The genus Proechimys was referred to the family

Echimyidae by Miller and Gidley (1918), and to the

subfamily Echimyinae by Ellerman (1940) and

Landry (1957). Patterson and Pascual (1968) recognized five subfamilies in their synopsis of the Echimyidae: Adelphomyinae, extinct forms only; Echimyinae

and Dactylomyinae, Recent forms only; Heteropsomyinae and Myocastorinae, extinct and Recent forms.

Under Patterson and Pascual's arrangement Proechimys is included in the Heteropsomyinae.

The earliest known representatives of the Echimyidae are Deseadomys arambourgi and D. loomisi, both

of the Deseadean (lower Oligocene) of Argentina

(Wood and Patterson, 1959). Wood and Patterson

(1959) stated that the Adelphomys group (including

Deseadomys) seemed to represent a separate line that

did not give rise to any Recent echimyids. According

to Patterson and Pascual (1968) this assemblage, including Paradelphomys and Xylechimys, represents the

subfamily Adelphomyinae.

The earliest fossil forms of Proechimys are of late

Pleistocene or Recent age and thus shed no light on the

early history of the genus. Moojen (1948) suggested

that evolutionary development in Proechimys has been

directed toward species with increased numbers of

counterfolds in the cheek teeth. For evidence, Moojen

mentioned the low counterfold numbers in the cheek

teeth of fossil Proechimys from Lagoa Santa, Brazil,

and like numbers in the teeth of species in the subgenus

Trinomys. An increased number of counterfolds along

with greater species diversity is present in the subgenus

Proechimys, and may be an indication that the multicounterfold line of spiny rats is more "successful" in an

evolutionary sense. Convincing evidence, however, is

definitely lacking on this point.

The name Proechimys was proposed by Allen

(1899b) using Echimys trinitatis Allen and Chapman,

as the genotype. His concept of the genus included species of Hoplomys and Mesomys, presently accorded full

generic rank in the family Echimyidae. Thomas (1921)

proposed the subgenus Trinomys to characterize the

spiny rats of southeastern Brazil that have a distinctive

mainfold arrangement in the cheek teeth. Tate (1935)

presented a taxonomic history of the genus Proechimys,

later supplemented by Ellerman (1940), Hershkovitz

(1948), Moojen (1948), and Cabrera (1961). Most

of the discussion that follows concerns members of the

subgenus Proechimys.

Moojen (1948) and Hershkovitz (1948) pointed

out that Mus ( = Proechimys) guyannensis E Geoffroy

St. Hilaire, 1803, antedates Echimys ( = Proechimys)

cayennensis Desmarest, 1817; however, most workers

prior to 1948 had used the latter name.

Ellerman (1940) proposed that the majority of the

50 named forms of Proechimys be included in four

species: P. cayennensis, with 29 subspecies; P. albispinus, 2 subspecies; P. iheringi and P. (Trinomys)

setosus, monotypic. He also retained five other forms as

full species within the cayennensis group (P. vacillator,

P. hendeei, P. rattinus, P. canicollis, and P. dimidiatus). Osgood (1944) reported on Proechimys from

Ecuador and Peru without following Ellerman's arrangement, although he suggested that several named

forms did not merit specific rank.

Moojen (1948), working with Brazilian forms, recognized four species in the subgenus Proechimys (P.
NUMBER 35

goeldii, P. semispinosus, P. longicaudatus, and P. guyannensis). Hershkovitz (1948), primarily concerned

with forms found in Colombia, tentatively accepted

Ellerman's contention that P. guyannensis was a composite species. In addition, Hershkovitz regarded P.

hendeei as distinct from P. guyannensis and erected a

group based on P. quadruplicates Hershkovitz, 1948.

Moojen (1948) relied heavily on pelage characteristics

and Hershkovitz (1948) on patterns of enamel folds.

Cabrera (1961) listed 57 forms in the genus Proechimys, following closely the arrangement of Moojen

(1948).

Although no attempt is made in this study to evaluate the subfamilial affinities of Proechimys, it is considered to be a valid genus of the Echimyidae. It was

hoped that this study of morphological variation in

various populations of Proechimys might clarify the

specific status of several nominal forms in the genus,

particularly P. canicollis, P. guyannensis, P. hendeei,

P. longicaudatus, P. quadruplicatus, and P. steerei.

Materials and Methods

SPECIMENS.—In this study, 165 specimens (including 42 bacula, 165 skulls, and 152 skins) were examined. Most of the specimens were those collected

by the Middle America Research Unit (MARU) in

connection with its field investigations of hemorrhagic

fever in Bolivia and adjacent areas during 1964-1966.

The MARU specimens were submitted to the Mammal Identification Service, Division of Mammals,

Smithsonian Institution, for identification and deposition in the mammal collections of the National Museum of Natural History. Additional specimens from

Brazil and Colombia were also examined. All specimens examined are deposited in the National Museum

of Natural History (USNM).

Localities on the map (Figure 1), numbered consecutively from north to south, indicate the major collecting sites of specimens. These and other localities

are listed alphabetically by country in the gazetteer.

"Population Accounts" refer to the numbered localities

in Figure 1. Morphological variants within some populations have been arbitrarily designated A, B, C, D, or

E to aid in description, comparison, and discussion. In

the "Specimens examined" sections of the population

accounts, the specific localities are arranged from north

to south, and then west to east at similar latitudes.

FIGURE 1.—Map showing principal collecting localities (refer

to gazetteer and specimens-examined sections for detailed locality data): 1 Villanueva, 2 Hyutanaham, 3 Porto Velho,

4 Rio Branco, 5 Riberalta, 6 Puerto Maldonado, 7 San Joaquin, 8 Cafetal, 9 San Ignacio, 10 Warnes, 11 Limao Balsa,

12 Corumba.

GAZETTEER

(Numbers in parentheses refer to localities in Figure 1)

BOLIVIA

Cafetal (8): 13°26'S, 64°35'W; SE of San Joaqufn,

Mamore, Beni.

Juan Latino: 17°24'S, 63°07'W; 13 km NNE

Warnes, Warnes, Santa Cruz.

La Abra: 17°26'S, 63°06'W; 18 km NE Warnes,

Warnes, Santa Cruz.

Riberalta (5) : 10°59'S, 66°06'W; Vaca Diez, Beni.

San Ignacio (9): 14°53'S, 65°36'W; Moxos, Beni.

San Joaquin (7): 13°04'S, 64°49'W; Mamore, Beni.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Santa Rosita: 17° 34'S, 63 ° 13'W; 3 km SW Warnes,

Warnes, Santa Cruz.

Warnes (10): 17°30'S, 63°10'W; Warnes, Santa

Cruz.

BRAZIL

Caceres: 16°04'S, 57°41'W; Caceres, Mato Grosso.

Corumba (12): 19°01'S, 57°39'W; Corumba, Mato

Grosso.

Hyutanaham[ = Huitanaa, Hyutanaha](2) : O7°4O'S,

65°46'W; Labrea, Amazonas.

Limao Balsa (11): 16°03'S, 58°09'W; 48 km W

Caceres, Caceres, Mato Grosso.

Porto Velho (3): 08°46'S, 63°54'W; Porto Velho,

Rondonia.

Rio Branco (4): 09°58'S, 67°48'W; Rio Branco,

Acre.

Santa Theresa: 19°15'S, 57°46'W; 7 km WSW

Urucum, Corumba, Mato Grosso.

Urucum: 19°09'S, 57°38'W; 22 km S Corumba,

Corumba, Mato Grosso.

COLOMBIA

Villanueva (1): 10°37'N, 72°58'W; Valledupar,

Magdalena.

PERU

Puerto Maldonado (6) : 12°36'S, 69°12'W; Tambopata, Madre de Dios.

Most of the specimens examined in the study were

collected near streams or rivers (except those of Proechimys canicollis from Villanueva, Colombia, see

Hershkovitz, 1948) which are part of the two major

drainage systems of South America. The Amazon system drains most of northern and northwestern Brazil,

most of Bolivia, and portions of Peru, Ecuador, Colombia, and the Guianas. The Parana-Paraguay system

drains Paraguay, Uruguay, most of Argentina, and

western and southwestern Brazil. Most of the localities

(2-10, in Figure 1) are located along streams in the

Amazon system. A region of higher elevation and drier

climate separates the two drainage systems in southeastern Bolivia (Roseveare, 19481. Extensions of the

tropical rain-forest follow the streams of the Amazon

system, and then merge with the campo of Mato

Grosso, Brazil, and the Gran Chaco of southeastern

Bolivia (Smith and Johnston, 1945; Roseveare, 1948).

METHODS.—Specimens were sorted by age, sex, and

locality to assess the degree of individual variation

prior to analyzing variation between populations. Five

age classes were established on the basis of tooth wear

but only adults (classes IV and V) were statistically

analyzed. Secondary sexual variation was not significant and both sexes of like age classes were combined

for population comparisons.

Specimens from one locality, San Ignacio, Bolivia,

were sorted into various combinations of age classes

and sexes to assess intrapopulation variation. Pictet

(1841) suggested that Echimys ( — Trinomys) setosus

9 i

FIGURE 2.—Occlusal views of left upper (a-e) and lower

(/-;") cheek teeth in Proechimys guyannensis. Age classes

(roman numerals) and respective USNM catalog numbers:

a, I, 364103; b, II, 364104; c, III, 364121; d, IV, 364114;

e, V, 364129; /, I, 364103; g, II, 364104; h, III, 364121; i,

IV, 364114; j , V, 364129. (The uppermost tooth in each

series is premolar 4. In a-e, the labial side is on right border

of the tooth row; in /-;, labial side is on left. All specimens

are males from San Ignacio, Bolivia.)
NUMBER 35

and E. (= Trinomys) myosurus were age variants of E.

(= Proechimys) cayennensis. Some taxa in Proechimys

are probably based on age variants (Tate, 1939). Allen

(1894), in examining large series of Neotoma micropus, suggested that age differences may be incorrectly

interpreted as subspecific or specific differences. Dice

(1932) recognized this factor in Peromyscus and suggested that only individuals of similar age groups be

compared in studies of geographic variation.

Degree of tooth wear is frequently utilized to establish "age" categories for comparisons of populations.

Handley (1959, p. 4) reported that "Tooth wear appears to be a reliable criterion of age." in Hoplomys.

Moojen (1948) recognized four age classes in Proechimys, based on pelage characteristics and degree of

tooth wear. Similarly, five age classes were established

in this study, based primarily on tooth wear. An inherent difficulty of this aging technique is that tooth

wear may not correlate with chronological age, and

may be affected by diet, health, and habitat of the

mammal. But for statistical comparisons of populations the technique proved useful.

Changes in the occlusal pattern of the teeth are illustrated in Figure 2 and discussed below:

Class I (Figure 2a, f): Only P4-p4 and Ml-ml

are at occlusal level and show signs of island formation from wear on the counterfolds. The middle

island has not formed in P4 and p4. This class corresponds to the juvenile age recognized by Moojen

(1948).

Class II (Figure 2b, g): All enamel islands appear

in P4, p4, and Ml. M2 and m2 appear at occlusal

level, but no islands have formed. The first sign of an

incipient anterior island in ml appears in this class.

Class III (Figure 1c, h): The enamel islands in

P4 and Ml are similar to those of class II, but show a

reduction in size through wear; M2 is similar to Ml.

In ml and m2 small incipient anterior islands form;

M3 and m3 may show slight wear, although they are

usually still below occlusal level where wear occurs. Age

classes II and III encompass Moojen's adolescent

category.

Class IV (Figure 2d, i) : The islands in P4 and p4

are reduced in size; the incipient islands of ml and m2

merge with the middle island to form Y's, and after

much wear are lost. M3 and m3 are at occlusal level,

although island formation may not be completed in

m3. This class includes most of Moojen's adult

category.

Class V (Figure 2e, j): Many of the islands of P4

and p4 are greatly reduced in size or lost entirely.

The islands of Ml and ml frequently divide into additional smaller islands, those of M2 and m2 are reduced

in size, and those of M3 and m3 show complete formation. Only the oldest individuals of this class would

correspond to Moojen's senile category.

Ten cranial and four bacular measurements were

made on the largest series of specimens (from San

Ignacio, Bolivia), using dial calipers accurate to 0.1

mm. These measurements are described below and

illustrated in Figure 3.

Nasal length: From median anterior to posterior

points (exclusive of notch) on nasal bones, a to a'.

Nasal breadth: Greatest distance across nasal

bones, b to b'.

Zygomatic breadth: Greatest distance across zygomatic arches, c to c'.

Palatal length: From anteriormost point of premaxillae to anteriormost point of postpalatal notch,

d to d'.

Maxillary breadth: Greatest with across maxillary

bone midway between P4 and Ml, e to e'.

FIGURE 3.—Views of skull and baculum of Proechimys showing points of reference for measurements.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Alveolar length, upper tooth row: Distance between anterior alveolar margin of P4 and posterior

margin of M3, f to f.

Mastoidal breadth: Greatest distance across mastoid bones, g to g7

.

Condylobasal length: From anteriormost point of

premaxillary bulge to posterior level of occipital condyles, d to h.

Greatest length of skull: From anteriormost point

of nasal bones to posteriormost point on occipital bone,

a to i.

Rostral depth: Least vertical distance from anterior alveolar border of P4, f to j .

Bacular length: Greatest length, k to k'.

Bacular width, anterior: Greatest transverse distance across ventrally projecting elements, 1 to 1'.

Bacular width, posterior: Greatest transverse distance across base, m to m'.

Bacular depth, anterior: Greatest distance between

dorsal and ventral elements, n to n'.

Coefficients of variation (V) were calculated according to the method of Haldane (1955) for all cranial,

bacular, and external measurements of specimens from

San Ignacio (Table 1). Measurements having large

F-values were not used as indicators of interpopulation variation. Broken skull parts prevented use of

some measurements with low F-values. The measurements used were condylobasal, palatal, nasal, and alveolar lengths; zygomatic, mastoidal, and maxillary

breadths; and rostral depth. Coefficients of variation

(F) were computed for different groupings of age

classes and sexes to see if secondary sexual variation

was significant (Table 2). The F-values were generally smaller when sexes were grouped in a single age

class and larger when age classes of like sexes were

combined. In all combinations there was a significant

overlap of measurements when males were compared

with females. Although females were slightly smaller

than males in age-class IV, they closely approximated

male growth in age-class V. The smallest F-values

occurred in single-sex and age-class grouping, but

these combinations involved small sample sizes, making

statistical comparisons difficult. Sample sizes were,

therefore, increased in the different populations by

grouping sexes together within each age class.

The arithmetic mean (X), standard deviation (SD)

and standard error (SE) were calculated for all populations of adequate sample size as defined by Simpson,

et al. (1960). Sample sizes were increased by pooling

specimens from areas within 30 km of each major locality. Student's Mests were performed on two measurements (condylobasal length, zygomatic breadth) to

TABLE 1.—Coefficients of variation (V) for bacular, cranial, and external measurements in a sample (N) of Proechimys guyannensis from San Ignacio, Bolivia

pleasure men t

Rostral depth

Zygomatic breadth

Mastoidal breadth

Alveolar length

Palatal length

Greatest length of skull

Maxillary breadth

Condylobasal length

Hind foot length

Bacular width, anterior

Nasal length

Nasal width

Total length

Tail length

Bacular width, posterior

Bacular length

Ear length

Bacular depth, anterior

Males, Age-Class IV

JV

13

12

12

13

9

8

13

9

13

8

13

13

11

11

6

7

13

8

V

1.32

2.76

2.85

3.03

3.49

3.53

3.69

3.78

4.85

5.02

6.34

6.47

6.60

7. 12

7.80

8. 15

11. 10

11.30

Males, Age-Class V

N

8

8

8

8

7

5

8

5

8

4

8

8

6

6

6

6

8

6

V

3.38

1.41

2.72

4.75

3.42

2.88

3.91

3.72

3.59

13.32

5.39

1.74

4.30

4.98

7.28

10.66

8. 16

21.36
NUMBER 3 5

TABLE 2.—Coefficients of variation (V), means (X), and standard deviations (SD) for three cranial measurements showing differences in sorting methods in a sample (A") of Proechimys guyamtensis from San Ignacio, Bolivia

Sorting Method

Age classes, sexes combined

Males, age classes combined

Kemales, age classes combined

Sexes combined, age-class V

Sexes combined, age-class IV

Males, age-class V

Females, age-class V

Males, age-class IV

Females, age-class IV

A

35

20

IS

n

17

8

12

10

Zygomatic Breadth

V

5. 12

2. 16

f>. 08

1.72

4.82

1.41

1.48

2.7b

4.94

-V ±

24.8 ±

25. 1 ±

24.3 i

25.9 ±

24.3 -t

25.7 ±

26.2 =

24.7 ±

23.4 ±

1 SD

1.27

0.54

1.67

0.44

1. 15

0. 35

0.37

0. 67

1. 13

N

31

21

11

13

19

8

5

13

6

Rostral Depth

V

5.52

4.99

6. 33

2.75

3. 95

3. 38

1. 18

3. 37

0.40

.V

12. 1

12.2

11.9

12.7

11.7

12.8

12.6

11.9

11.2

±

4.

±

4-

4-

i-

±

±

±

4.

1 SD

0.67

0.60

0.73

0.34

0.46

. 0. 42

0. 14

0.39

0.04

N

32

21

11

13

19

8

5

13

6

Maxillary Breadth

V

5.96

5.87

6.50

3.41

3.68

3.91

2.91

3.69

3.26

X

8 .2

8 .2

8. 1

8.7

7.9

8.7

8 .6

7.9

7.7

±

4-

±

±

4-

±

4-

4-

1 SD

0.49

0.48

0.52

0.29

0.29

0. 33

0.24

0.29

0. 24

test differences between some localities. Bar graphs,

similar to those of Hubbs and Hubbs (1953), were

constructed for all cranial measurements to demonstrate variation between 11 populations. No statistical

analyses were made of dental or pelage characteristics,

and small sample sizes prevented statistical treatment

of bacula.

, Dried phalli were removed where possible from the

skins of specimens and the bacula processed according

to the method of Friley (1947), in part.

Tooth nomenclature follows that of Hershkovitz

(1948) and Moojen (1948), in part. Lowercase (p,

m) and capital (P, M) letters designate lower and

upper cheek teeth, respectively. All formulae given in

the locality accounts and all references to counterfolds

refer to the number of outer folds in the upper and

the number of inner folds in the lower cheek teeth

(c.g., 3/3-3/2-3/2-3/2; in Figure 2d, i). Pelage terminology follows Moojen (1948). Aristiforms, comparable to guard hairs in other mammalian groups, are

long, broad, flattened hairs that are frequently spinous.

Sctiforms ( = overhairs) are narrower than aristiforms

and less spinous. Capitalized color terms (Ridgway,

1912) are used in descriptions of pelage in the population accounts.

Population Accounts

FIGURES 1. 4

Villanueva, Colombia (1)

DESCRIPTION.— External: Aristiforms long (19-20

mm ) and narrow (0.4 mm^. soft, hidden by setiforms:

:»5fi 57 N O 7»> - 2

dorsum pale. Light Ochraccous Buff to Ochraceous

Buff; venter with white inguinal and axillary patches,

bordered by Smoke Gray areas; feet with numerous

white hairs; tail not sharply bicolor, but lighter below.

Fof additional descriptions, see Allen (1899a, p..200)

and Hcrshkovitz (1948, p. 131).

Skull: Nasals long, extending considerably beyond

premaxillary-frontal suture; incisive foramina short

and wide, expanded anteriad; palatal notch extending

to middle, or slightly anterior to, M3; hamular process

of pterygoid narrow, constricted at base; posterior zygomatic process involving squamosal and portion of

parietal; temporal ridge short.

Teeth: Counterfold pattern 2/2-2/2-2/2-2/2 in all

specimens examined.

Baculum (Figure 4a, b ) : Long and slender, slightly

convex dorsad; basal and apical regions wider than

middle portion; base thickened, with concave depression ventrad; apical region may possess wings directed ventrolaterad: width much greater than depth,

especially in middle.

COMPARISONS.— Pelage finer and grayer, and incisive formina broader and shorter than in all other

Imputations; baculum similar to that in Hyutanaham

and Porto Velho populations. See Hershkovitz (1948,

pp. 131-132) for comparisons with Proechimys guyannensit mincae in Colombia.

REMARKS. • -Proechimys canicollis (Allen 1, appears

distinctive in having a counterfold pattern that is not

jjossessed by other members of the subgenus Proechimys. Ecological differences between this species and

Proechimys !>uyannensis mincae were reported by Allen

(1904. p. 440. quoted from field notes of Herbert H.
8

Smith) for the localities where the two species were

found together. Hershkovitz (1948) considered P. canicollis to be annectant between P. guyannensis and the

subgenus Trinomys. On the present evidence, specimens from Villanueva are retained as P. canicollis.

SPECIMENS EXAMINED.—Total 16, from Colombia:

Magdalena.—Valledupar: Villanueva, 16 (12 $ $ :

USNM 280123,280125, 280127,280130-131, 280136-

V?

Wl

(I

I

5 mm

i i

FIGURE 4.—Ventral views of Proechimys bacula. Taxa, localities, age classes (roman numerals), and USNM catalog

numbers, listed in that order: a, b, P. canicollis, Villanueva,

Colombia, IV, 280131 and 280125, respectively; c, d, P.

guyannensis, Riberalta, Bolivia, IV, 363986 and 364005,

respectively; e, f, P. guyannensis, Puerto Maldonado, Peru,

IV, 364026 and 364014, respectively; g, P. guyannensis, San Joaquin, Bolivia, V, 363982; h, P. guyannensis,

Cafetal, Bolivia, IV, 391403; i, ;, P. guyannensis, San Ignacio,

Bolivia, IV, 364114 and 364133, respectively; *, P. guyannensis, Corumba, Brazil, IV, 364075.

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

140, 280142, 28150; 4 9$ : USNM 280126, 280133,

280141,280149).

Hyutanaham, Brazil (2)

DESCRIPTION.—External: "Upper parts Mars

Orange on back, grading to Ochraceous-Tawny on

sides . . . Aristiforms on middorsal region: Grayish

basally, gradually blackening toward tip; total length

[of aristiforms] 16-19 mm; maximum width, 0.5 mm."

(Moojen, 1948, p. 338.) For additional characters of

Proechimys steerei, see Goldman (1911, pp. 238-239).

Skull: Nasals broader anteriad, tapering posteriad;

incisive foramina short, narrow, slightly expanded in

middle; palatal notch extending to middle of M3 or

slightly posteriad; posterior zygomatic process confined

mostly to squamosal; temporal ridge short, weak.

Teeth: Counterfold pattern variable, 3/4-3(4?)/

3(4?)-3(4?)/3(4?)-3(4?)/3(4?); with wear on the

molars a fourth island may appear.

Baculum: Long (7.7 mm and narrow (1.9 mm at

anterior end), with ventral groove and convex dorsum;

basal and apical regions wider than middle; widest

anteriad, wings project ventrad. Similar to Figure 4a

but longer and with more pronounced ventral groove

and apical wings.

COMPARISONS.—Color of dorsum similar to specimens from Porto Velho and Rio Branco, although more

reddish; aristiforms similar to those of Rio Branco population; counterfold pattern distinctive, but similar to

that of specimen C (USNM 391008) from Riberalta;

baculum similar to that of Proechimys canicollis, although longer and with more pronounced apical wings.

REMARKS.—Proechimys steerei Goldman, (typelocality, Hyutanaham, Brazil, Goldman, 1911, 1912)

was considered a subspecies of P. goeldii by Moojen

(1948). Hershkovitz (1948) included P. steerei in P.

guyannensis. The counterfold pattern of the upper

molars is complex and in this study has been interpreted differently than did Moojen (1948) and Hershkovitz (1948). There are probably three counterfolds

which could separate into four distinct islands through

wear.

In general appearance, Proechimys steerei is a distinctive form and may be worthy of at least subpecific

rank. It is impossible, however, to judge the merits of

including P. steerei as a race of P. guyannensis or P.

goeldii, without further study of the relationships of

these forms in the Amazonian region.
NUMBER 3 5

SPECIMENS EXAMINED.—Total 3, from Brazil:

Amazonas.—Labrea: Hyutanaham (type-locality), 3

(type, $, USNM 105535; topotyes: $, USNM

105536 9, USNM 105537).

Porto Velho, Brazil (3)

DESCRIPTION.—External: Aristiforms wide (0.8-

1.0 mm) and short (15-17 mm); dorsum OchraceousTawny mixed with many black hairs; venter white,

sharply demarcated from sides; feet Pinkish Buff to

Cinnamon-Buff; interspersed with white hairs; tail

sharply bicolor.

Skull: Nasals long (extending beyond infraorbital

foramen, USNM 364146) ; or short (extending to

infraorbital foramen, in 364145) ; incisive foramina

broader anteriad, tapering sharply posteriad; palatal

notch extending to middle of M3 (USNM 364146) or

midway between M2 and M3 (USNM 364145);

hamular process of pterygoid constricted at base, expanded in middle, and forming a sharp point distad;

posterior zygomatic process involving squamosal and

portion of parietal; temporal ridge evident, but not

forming a prominent line; zygoma sharply tapering

anteriad (USNM 364145) or approximately parallel

to long axis of skull (USNM 364146).

Teeth: Counterfold pattern 3/3(4)-3/3-3/3-3/3.

Baculum: None available for study.

COMPARISONS.—Similar in many external features

to the Rio Branco and Hyutanaham populations, but

aristiforms much wider and color slightly paler;

counterfold pattern similar to that in Rio Branco

population.

REMARKS.—Specimens from this locality are provisionally referred to Proechimys guyannensis, although

in coloration they are similar to P. steerei. The cranial

differences between USNM 364145 and 364146 probably represent variation within the population.

SPECIMENS EXAMINED.—Total 9, from Brazil:

Rondonia.—Porto Velho: 8 km N Porto Velho, 9 (4

$ $ : USNM 364146, 390351, 390353, 390355; 5

9 9 : USNM 364143-145, 390352, 390356).

Rio Branco, Brazil (4)

DESCRIPTION.—External: Aristiforms of medium

width (9.5-9.7 mm) and length (18-19 mm) ; dorsum

Cinnamon-Brown to Ochraceous-Tawny, grading to

Buckthorn Brown on sides; venter white, tail bicolor;

forefeet Prout's Brown, hindfeet Buckthorn Brown.

Skull: Nasals extending to level of infraorbital

foramen, not broadened anteriad; hamular processes

of pterygoid similar to those of Porto Velho specimens,

but tips, less pointed; posterior zygomatic process involving squamosal and part of parietal; temporal ridge

not evident.

Teeth: counterfold pattern 3/4(3)-3/3-3/3-?/?

Baculum: Long and slender, convex dorsad; basal

and distal regions slightly expanded laterad; slight median groove along ventral surface; similar to that in

specimen from Hyutanaham, but smaller.

COMPARISONS.—Similar to specimens from Porto

Velho, although somewhat darker; aristiforms similar to those from Hyutanaham.

REMARKS.—Only age-class III specimens were

available for study, which makes comparisons with

older specimens of questionable value.

Specimens from this locality are very similar in external appearance and dental pattern to those from

Hyutanaham. The dental similarities are more evident if the specimens from Hyutanaham truly have

only three counterfolds in the upper molars (see remarks under Hyutanaham, Brazil, account). However,

the Rio Branco specimens could also fall within the

range of variation for Proechimys guyannensis, based

on cranial dimensions and a conservative interpretation of the number of counterfolds.

SPECIMENS EXAMINED.—Total 3, from Brazil:

Acre.—Rio Branco: 3-4 km S Rio Branco, 3 (2 $ $ :

USNM 364142, 364147; 9, USNM 364148).

Riberalta, Bolivia (5)

DESCRIPTION.—External: Aristiforms of A (USNM

363991, 363993, 363995, 363998, 364005, 364006,

364009) and B (USNM 363986, 363988) specimens of

medium length (18-19 mm) and width (0.5-0.6 mm);

those of C (USNM 391008) short (16-17 mm) and

narrow (0.3 mm); dorsum of A and B OchraceousTawny, grading to Buckthorn Brown on sides; dorsum

of C Cinnamon-Brown to Ochraceous-Tawny, with

many black hairs; feet of A Buffy Brown, those of B

white and those of C white and Mummy Brown.

Skull: Nasals in A, B, and C long, broadened anteriad, extending posteriad to level of infraorbital foramen, or slightly behind; incisive foramina in A, B, and

C slender, slightly expanded in middle; palatal notch
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

variable in A and B, extending anteriad to rear margin

of M3 or to middle of M3; palatal notch in C extending1

 to middle of M3; posterior zygomatic process in

A and B involving squamosal and expanded laterad,

that in C involving squamosal, not expanded laterad;

temporal ridge in A and B not pronounced, involving

one-half of parietal, that in C not pronounced, involving one-fourth or less of parietal.

Teeth: Counterfold pattern in A, 3/3(4)-3/3(4)-

3/3(4)-3/3(4), in B 3/3-3/3-3/3-3/3, and in C,

3(4?) /4-3(4?) /3-3(4?) /3-3?/3.

Baculum: In A (Figure 4rf) long and slender,

slightly convex dorsad; basal one-fourth thickened,

under than apical region; ventral groove evident, shallow in middle; apical wings project sharply ventrad.

In B (Figure 4c) long and broad, convex dorsad: basal one-third thickened, lateral margins surrounding a

deep depression: apical wings broadly expanded ventrad, lateral margins straight-edged or rounded; shaft

noticeably narrower in middle, shallow. No baculum of

C was available for study.

COMPARISONS.—External and cranial characters of

A and B similar, but bacula markedly different (see

above) ; coloration in C much darker and aristiforms

shorter and narrower; cranial dimensions of A and B

much larger than in all populations examined; coloration in A and B darker than m San Ignacio, Warnes,

Liiiwm Balsa, and Corumba populations, but lighter

than C and specimens from Gafetal and San: jtoaquin.

REMARKS.—Bacular difference is the ba*is for, distinguishing between two morphological variants (A,

B) in this popufation. Evidence from Other; rodent

groups (see Burt and Barkalow, 1942; Hershkovitz,

1962 and 1966) indicates that the differences in bacular shape and structure between A arid B are greater

than-could be expected from one population of a single

species. In general, age and size did not correlate with

bacular type, and the largest specimens (A) had small

bacula (Figure 4<i). Only two specimens of B had

bacula and no clarifying ecological information was

available. It is premature to suggest that these two

variants may represent sibling species and, therefore,

they are referred to Proechimys guyanneruis. Subspecific assignment is largely conjectural although the description by Thomas ( 1901 ) for Proechimys guyannensis bolivianus agrees in some respects with the specimens. Also. Riberalta is on the Rio Beni and the typelocality for P.g. bolivianus is near the Rio Mapiri, an

upper tributary of the Rio Beni.

Variant C differs markedly.from A and B. In several features, C compares favorably with the description given for Proechimys quadruplicatus Hershkovitz,

although the dorsal medial color band is not so evident, and the pattern of the upper molars is similar to

P. steerei from Hyutanaham. The "fourth" fold in Ml

and M2 is small and slightly posteriad to the third fold.

However, the evidence strongly favors assigning this

specimen to Proechimys quadruplicatus.

SPECIMENS EXAMINED.—Total 23, from Bolivia:

Panda—Madre de Dios: 13 km N\V Riberalta, 1 ( £ ,

USNM 364009) ; 5 km NW Riberalta, 3 (2 S 3 i

USNM 364005-006; ? , USNM 364007) ; 3.5 km NW

Riberalta, 3 (2 £ £ : USNM 363996, 363998; 9,

363997). Beni.—Vaca Die,: 13 km NE Riberalta, 5

(2 6 £: USNM 363999, 364002; 3 9 9; USNM

364000-001, 364003) ; 10 km NNE Riberalta, I ( 9 ,

USNM 391008) : 13 km W Riberalta, 1 ( £ , USNM

363991) ; 2.3 km W Riberalta, 1(9 , USNM 363990) ;

Riberalta, 8 (566: USNM 363985-986, 363988,

363993, 363995; 399 : USNM 363987, 363989,

363994).

Puerto Maldonado, Peru (6)

DESCRIPTION.—External: .Aristiform s in D

(USNM 364012, 364014, 364026) long (18-22 mm)

and of medium width (0.5-0.7 mm), those of E

(USNM 364149, 364151, 390367) short (16 mm)

and of medium width (0,6 mm); dorsum of D

Cinnamon-Brown, grading to Buckthorn Brown on

sides, that of E Ochraceous'-Tawny, mixed with some

black hairs, feet of D Saccardo's Umber with some

white hairs, those of E white; ventep white and tail

bicolorin both D and £..

Skull: • iNasals in P broader anteriad, extending

posteriad to infraorbital foramen; nasals in E long and

slender, broadly rounded posteriad, with small "internasal" bone situated mediad in the frontonasal suture;

incisive foramina in D long and narrow, those in E

shorter and broader; palatal notch variable in D, extending anteriad to rear margin of M3 or anteriad to

middle of M3; palatal notch of E reaching posterior

margin of M2; hamular process of pterygoid broadened and supraorbital ridge not massive in D and E:

posterior zygomatic process expanded laterad in D, but

not in E; temjjoral ridge weak, extending across parietal in D, more pronounced in E.
NUMBER 35

Teeth: Counterfold pattern in D, 3/3-3/3(2)-

3/3-3/2(3), in£, 3/3-2(3?)/3-2(3?)/3-2(3?)/3.

Baculum: In D (Figure \e, f) long, broadened

anteriad, convex dorsad; apical wings involving onethird of length, directed ventrad; ventral groove present, less pronounced in basal one-third; basal region

somewhat thickened, with medial notch, but Lateral

margins not excessively rugose; middle region much

narrower. Xo bacula of E were available for study..

COMPARISONS.—Variants D and E darker than all

Bolivian and Mato Grosso populations examined; aristiforms similar to those of Bolivian and. Ma.to Grosso

populations; posterior zygomatic process in D more

widely expanded laterad than in E; palatal notch of E

extending further anteriad than in D or other populations examined.

RT.MARKS.—The character of the palatal notch in

E is distinctive and approaches the condition found in

Proechimys hendcei Thomas. But the specimens do not

possess other characters of P. hendeei mentioned by

Thomas (1926) and Hershkovitz (1948). The coloration is paler and p4 has only three counterfolds.

In D the cranial, dental, and, external characters lie

within the ranges observed in specimens of Proechimys

guyannensis from other localities, although the bacula

are distinctive. In external characters the specimens

from this locality approach the conditions described

for. Proechjrnys guyannensis boliznanus. The bacula,

however, are similar in length and width to those

f rorn Villanueva, Colombia, ,and northwestern Brazil.

On the present evidence,!) and E seem referable to

.Proechimys , guyannensis, although their subspecific

affinity has not been determined.

SPECIMENS EXAMINED.—Total 24, from Peru:

Madre de Dios.—Tambopata: 6 km W Puerto Maldonado. 1 ( 3 .USNM 364013) ; 4.5 km. W Puerto

Maldonado, L- ( 9 , USNM 364030) : 4 km W Puerto

Maldonado, 2 (2 9 9 :USNM 364150-151); Puerto

Maldonado. 4 ( & , USNM 364014: 3 9 9 •: USNM

364015, 364149, 3903661; 12 km E Puerto Maldonado, 4 {2 6 6 : USNM 364031-032: 22 9 : USNM

364033-034) ; 1.5 km S Puerto Maldonado, 6 (6 6 6 :

USNM 364019-020. 364025-026V; 3 km SW Puerto

Maldonado, 1 (9 . USNM 364018); 3.5 km SW

Puerto Maldonado, 1 .' <$ . USNM 364017! : 4 km SW

Puerto Maldonado. 1,9 , USNM 364021) ; 1.5 km SE

Puerto Maldonado, 1(3 , USNM 364024) ; 4 km S

Puerto Maldonado, 1 f 6 , USNM 364012) ; 15 km S

Puerto Maldonado, 1 ( <J , USNM 364011).

San Joaquin, Bolivia (7) y . v

DESCRIPTION.—External:. Aristiforms leMg (28^24

mm) and of medium width (t).7 n*Hti) ; dorsun>Ochraceous-Tawny grading to Buckthorn Browri oft*idl

es,

with a few black hairs; venter white, feet BufTy Brown

to white; tail sharply bicolor, dark a.boye,;)y)l#te)3elciwj

feet white and brown.

Skull:1 Nasals' slightly broadened anterTad1, 'e'ndmg

posteriad at level of ihfraoVbital foramen'i incisive fofa^-

mina long and narrow, slightly broader anteriad; pralatal notch extending to middle of'M3; hamular process

of ptengoid slightly constricted kt'basb, arid expancled

in middle; supraor&ital ridge x'tty pTorrtfnent, pdsteriBf

zygomatic process involving scftiarnosiif' arid p/atti!6f

parietal; temporal ridge extending posrena'd'to bas'locicipital crest, but not pronouticed. ' ''' •'•!"••;''•'••

Teeth: Counterfold pattern 3/3-3/3(2^3/2(3)'-

3(2) /2(3) ; the retention of art isolated ariterior island

in m2 and m3 accounts for some of the'variability.

Baculum (Figure 4g) : Long arid broad, convex

dorsad; basal one-third thickened and rugose, with

ventral depression; lateral wings project ventrad, their

distal margins straight-edged; ventral groove evident

throughout length, shallow in middle!

COMPARISONS.—Coloration similar to that of Ca'fetal population, darker than specimens from San Ignacio, Warnes, Limao Balsa, Corumba, ancT Proechimys

guyannensis^ from Riberalta; aristiforms similar to

those of Cafetal population, but longer; baculum distinctive> most, simila^ to that{ of the specimen from

Cafetal. . ...... . . \: , :ti

REMARKS.—Accordwg to Moojen , .(1-94^), Preechimys 1. longicaudatus (Rengger) and P. longicaudatus leucomystax Ribeiro, from western. Mato Qrosso,

Brazil, have a counterfold arrangement of 3/3-3/2-

3/3-3 II. Some of the specimens from San joaquinand

Cafetal approach thig dental arrangement. The two

baculi available from the San Joaquin and Gafetall

specimens are distinctive, but show similarities with

those from Riberalta, San Ignacio, and Corumba. This

evidence indicates a considerable overlap in characters

between these two populations and those from Puerto

Maldonado, Riberalta, San Ignacio, Warnes, Lima6

Balsa, Corumba. Specimens from San Joaquin and

Cafetal were assigned to Proechimys guyannensis, suggesting that the San Ignacio, Warnes, Limao Balsa,

and Coruinba specimens may also be referable to P.

guyannensis.
12

SPECIMENS EXAMINED.—Total 4, from Bolivia:

Beni.—Mamore: San Joaquin, 1 {$, USNM

364929); 3.2 km SE San Joaquin, 3 (39$ :

363981-983).

Cafetal, Bolivia (8)

DESCRIPTION.—External: Similar to specimens

from San Joaquin, but aristiforms shorter (19-20

mm).

Skull: Nasals broadened anteriad, extending posteriad to level of infraorbital foramen; incisive foramina narrow anteriad and posteriad; palatal notch extending anteriad to middle of M3; posterior zygomatic

process involving squamosal and forming a thin shelf;

temporal ridge extending across parietal, not

pronounced.

Teeth: Counterfold pattern 3/3-3/3(2)-3/3-3/3.

Baculum (Figure Ah) : Long and broad, convex

dorsally and ventral groove present; apical wings

broader than basal region and projecting ventrad; distal margins of apical wings rounded; base broader than

middle, thickened on lateral edges; ventral depression

and medial notch present basally.

COMPARISONS.—Similar to specimens from San Joaquin, but incisive foramina broader anteriad. For additional comparisons, see under San Joaquin (p. 11).

REMARKS.—These specimens are probably referable to Proechimys guyannensis. See under San Joaquin

for reasons (p. 11).

SPECIMENS EXAMINED.—Total 3, from Bolivia:

Beni.—Mamore: Cafetal, 3 (2, USNM 391403;

29 9 : USNM 391402, 391406).

San Ignacio, Bolivia (9)

DESCRIPTION .—External: Aristiforms long (17-20

mm) and of medium width (0.5-0.7 mm) ; dorsum

Buckthorn Brown mixed with a few black hairs; venter white, not sharply demarcated from sides; hind

feet brown and white.

Skull: Nasals extending posteriad to infraorbital

foramen, slightly broadened anteriad; incisive foramina

long and slender, slightly expanded in middle; palatal

notch variable, extending anteriad to rear margin of

M2 or M3; hamular process of pterygoid constricted

at base, expanded in middle, and tapering to distal

point; supraorbital ridge prominent; posterior zygomatic process involving squamosal and small portion of

parietal; no temporal ridge extending onto parietal.

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Teeth: Counterfold pattern 3/3-3/2(3)-3/2(3)-3/

2(3); degree of tooth wear affects number of islands

formed in teeth of lower jaw (Figure 2).

Baculum (Figure \i, j) : Short and broad, convex

dorsally, with basal and apical regions expanded laterad; median proximal notch present (Figure 4i) or

absent (Figure 4;); ventral groove present, but may be

shallow in some specimens; basal one-third thickened

and rugose, lateral margins surrounding a ventral

depression.

COMPARISONS.—Coloration lighter than in Puerto

Maldonado, Cafetal, and San Joaquin, darker than in

Warnes, Limao Balsa, and Corumba populations;

counterfold pattern and artistiforms similar to those of

Warnes population, but overlapping with other populations ; baculum similar to that of Proechimys guyannensis, (B) from Riberalta.

REMARKS.—The San Ignacio and Warnes populations seem referable to Proechimys guyannensis, since

there is considerable overlap in cranial and dental characters, and dimensions, with the other populations of P.

guyannensis discussed earlier. Both of these populations

are near tributaries of the Rio Mamore. The specimens

from San Ignacio may be referable to Proechimys guyannensis securus Thomas, whose type-locality is on the

upper Rio Secure, a tributary of the Rio Mamore

(Thomas, 1902). This conclusion, however, cannot be

firmly substantiated by reference to the original description of P.g. securus.

SPECIMENS EXAMINED.—Total 32, from Bolivia:

Beni.—Moxos: 3.6 km NNE San Ignacio, 3 (3 $ $ :

USNM 364101, 364105, 364108); road to San Ignacio

Airport, 3 {$, USNM 364114; 29 9 : USNM

364113, 364115); San Ignacio, 21 (12 £ $ : USNM

364091-092, 364095-096, 364106, 364118, 364123,

364131, 364133, 364135-136, 364138; 9 9 9 : USNM

364098,364124-125,364132,364134, 364137,364139-

141); 1 km SW San Ignacio, 5 (5 S $ : USNM

364116-117, 364126-127, 364129).

Warnes, Bolivia (10)

DESCRIPTION.—External: Aristiforms long (18-20

mm) and narrow (0.5-0.6 mm) ; dorsum OchraceousBuff, mixed with a few black hairs; venter and feet

white; tail bicolor.

Skull: Nasals broadly rounded anteriad, gradually

tapering posteriad; incisive foramina broader anteriad

than posteriad, a median shelf evident posteriad;

palatal notch variable, extending to middle of M3
NUMBER 35 13

or to posterior one-third of M2; hamular process of

pterygoid not expanded or forming a distal point; supraorbial ridge prominent; posterior zygomatic process

involving squamosal and small part of parietal; temporal ridge extending across parietal.

Teeth: Counterfold pattern 3/3-3/2(3)-3/2(3)-

3/3.

Baculum: None available for study.

COMPARISONS.—Similar in coloration to specimens

from Corumba, paler than San Ignacio specimens,

darker than individuals of Limao Balsa populations;

aristiforms and counterfold pattern similar to those of

San Ignacio population.

REMARKS.—Specimens from this population share

features in common with those from San Ignacio,

Limao Balsa, and Corumba.

Warnes is near one of the upper tributaries of the

Rio Mamore, in the Amazon drainage system. Limao

Balsa and Corumba are located near tributaries of the

Rio Paraguay, in the Parana-Paraguay drainage system. In southeastern Boliva these two drainage systems

are separated somewhat by the higher elevations of

the Gran Chaco (Roseveare, 1948). Based on the similarities between the two Mato Grosso populations and

those of San Ignacio and Warnes, it is doubtful that

the Gran Chaco is a signficant dispersal barrier to

Proechimys.

The pelage of the Warnes specimens is similar to

that described for Proechimys I. longicaudatus by Moojen (1948). It is equally probable, however, that these

specimens may represent a pale population of Proechimys guyannensis.

SPECIMENS EXAMINED.—Total 22, from Bolivia:

Santa Cruz.—Warnes: Juan Latino, 1(9 , USNM

364051); La Abra, 1(5 , USNM 364073); 1 km

NNW Warnes, 6 (3 S $ : USNM 364065, 364067-

068; 3 $ $ : USNM 364062, 364064, 364070); 1.3 km

NE Warnes, 5 (2 S S : USNM 364071-072; 3 9 9 :

USNM 364059-061); Warnes, 1 (5 , USNM

391009); Santa Rosita, 8 (5 $ $ : USNM 364048,

364050, 364053-054, 364056; 3 9 9 : USNM 364062,

364064, 364070).

Limao Balsa, Brazil (11)

DESCRIPTION.—Aristiforms long (18-21 mm) and

of medium width (0.6-0.7 mm) ; pale, dorsum Ochraceous-Buff, mixed with a few black hairs; flanks and

shoulders lighter than dorsum; venter and feet white;

tail bicolor.

Skull: Nasals long and narrow, tapering posteriad ;

small, narrow, "internasal" bone was situated medially

in the frontonasal suture of most specimens (more than

half) ; incisive foramina long, rounded anteriad, the

lateral margins tapering sharply posteraid and forming

a median shelf; palatal notch extending near middle

of M3; hamular process of pterygoid narrowed at base,

not bulging in middle or forming a distal point; supraorbital ridge prominent; posterior zygomatic process

forming a shelf; temporal ridge ill-defined.

Teeth: Counterfold pattern 3/3-3/2(3)-3/3(2)-

3/2.

Baculum: None available for study.

COMPARISONS.—With the exception of the Villanueva population, the palest of the specimens examined; aristiforms and counterfold patterns similar

to those of San Ignacio, Warnes, and Corumba

populations.

REMARKS.—In external, cranial, and dental characters, the specimens from Limao Balsa are similar to

those from Corumba and Wames. The Limao Balsa

and Corumba specimens also show similarities in several features (see remarks for San Joaquin, Bolivia,

p. 11) with the description of specimens assigned by

Moojen (1948) to P. longicaudatus (Rengger). It is

possible, therefore, that the variation observed in Proechimys guyannensis (see previous accounts) may include the range of variation known for P. longicaudatus. Moojen (1948, p. 315) mentioned that P. guyannensis and P. longicaudatus were sympatric at Utiariti, Brazil, which supported his case for retaining

these forms as separate species. The range of variation

I observed in specimens from Limao Balsa and Corumba could include the morphological differences that

Moojen observed in his Utiariti specimens. Thus, I

have tentatively assigned the specimens from Limao

Balsa and Corumba to Proechimys guyannensis.

SPECIMENS EXAMINED.—Total 13, from Brazil:

Mato Grosso.—Caceres: Limao Balsa, 13 (7 $ 2 : US

NM 364037-039, 364042, 364044, 390371, 390374;

6 9 9 : USNM 364036, 364040-041, 364043, 390369,

390372).

Corumba, Brazil (12)

DESCRIPTION.—External: Aristiforms long (18-22

mm) and of medium width (0.6-0.7 mm); dorsum

Ochraceous-Tawny, grading to Ochraceous-Buff and

Buckthorn Brown on sides; feet tan to white; venter

white; tail bicolor.
14 SMITHSONIAN CONTRIIU'TIONS TO ZOOLOGY

Skull: Nasals Ion? and slender, extending postmad to infraorbital foramen, broadly rounded

anteriad: palatal notch extending anteriad to middle

of M3 or beyond: hatnular process of pterycoid narrowed at base, either rounded or pointed distad: supraorbital ridge very pronounced: posterior zygomatic

process involving squamosal and small part of parietal:

temporal ridge not extending across parietal.

Teeth: Counterfold pattern 3 3-3 3-3 '2'3 1-3/2.

Baculum (Figure 4r>: Short and broad, convex

dorsally: basal and apical regions expanded laterad:

median proximal notch and ventral groove present:

basal one-third thickened and rugose: apical wings

project ventrad. lateral margins straight-edged or

rounded. •

'' COMI'AKISOMS.—Darker than Limao Balsa specimen's but similar in other respects.

REMARKS: AS stated in the remarks for the Limao

Balsa populati6ri. the Corumba sjicciincns art* probably referable to Profchintys !?uyannen<n<. For additional information, see 'p. 13'.

SPECIMENS EXAMINED.—Total 13. from Brazil:

Mato Grosso.—Corumba: Corumba. 1 ; USNM

36407.1)-: 10 km NE Urucum. 5 (2 1 I : USNM

364D89. 390368: 3 9 9: USNM 364086-087.

^64^90 •: : Urucum. 2 <2 9 9 : USNM 364077-078' :

Santa Theresa. .=W2 * ! : USNM 364079. 364081: 3

? 9 : USNM 364080. 364084-085V

Intcrpopulation \'ariation

Some trends in bacular, cranial, dental, and external

features were noted in comparisons of populations, although these changes were not definitely clinal in

nature. Assessment of these trends was complicated by

the variability of individuals within a population. The

following comments on comparisons of morphological

feature* between populations gives some indication of

die nature of variability in spiny rats.

BACI.'I.I'M. -Hr>oper [ 10& 1 <. using three specimens,

apparently was the first to describe the baculum of a

Pr.>f-, lnr>!\<. No subsequent work on Pro, chimx* bacula

has been discovered in the literature. Thus, the present

Ntudy supplement* the available information on

lui'ular morphology in this genus.

A total of 42 bamla were available tor study, although t'-r ><.>:•.,<• !IN aiities none was found on the s|>eci-

> examined, anil for others th'* sample sizes were

sjii.ili. n.v»se available, however, did provide somr

e\:<!r:ur i.( :r:t'T [>«>[>'tlatioti variation. Iilustrations

i Figure 4 were made of bacula from most localities.

Most of the specimens from Bolivia and Corumba,

Brazil, had broad bacula. although the length was

variable Figure 4<. j,'. k). I he bacula from the

Puerto Maldonado. Peru, population were long and

slender, and with wide apical wings projecting ventrad

(Figure 4(\ /' . Bacula from Yillanueva, Colombia

were ver\* narrow i Figure 4a. /;'. In the Ribcralta.

Bolivia, population there were two types of bacula,

(see p. 101. markedly different from each other

(Figure 4r. d). Clinal variation was not appaient. although bacula from the San Joaquin and Ciafetal,

Bolivia. |>opulations Figure 4t,'. h \ showed some

mutual similarities with the long, slender bacula of

the northern populations and the broad bacula of the

southern j>opulations.

CRANIAL DIMENSIONS.—Of the eight cranial measurements analyzed (Figures 5-12). interpopulation

differences were most apparent in condylobasal ( Figure

")^. nasal I Figure 81. and palatal (Figure 11) lengths,

and to a lesser degree in zygomatic (Figure 7) and

I im3o Balto

Corumba

Fh;t RI> "> 8 \".»ri.iti"n in I"iir cranial dimrnsions between

11 |K>pulations "f Prose him \s, aco-dass I\": 5 mndylobasal

length, b maxillary breadth, 7 zygomatir breadth. 8 nasal

l'-ngth. Thr samplr si/r. .V. is shown by a number at the

rieht "f 'Mi h bar ur.i|)!: F'>r VJL< h sample the rante is shown

by .i horizontal Uv.r: the mean by a vertical line: two SE on

both sidrs of the mTin by a hlark bar: .ir.d one SD "n both

^i(!••^ i't the ir.can by tl >• I.lark plus open bars.
NUMBER 35 15

Villa

Hyutanaham

Porto Vtlho

Ribtralta

Puarto MoMonado

San Jooquin

Cafttal

Son r^nocio

Wdrnts

Limoo Balsa

Corumba

Villanutva

Hyutanaham

Porte Vtlho

Ribtralta

PiMrta MoMonado

San Jooqui'n

Cafttal

San Ignaclo

Warn**

Limao Balta

Corumbd

21 23

MaOokM Breodth Rostral Depth

12

25 28

PiJatal Length

8

Alvaotar Length

FIGURES 9-12.—Variation in four cranial dimensions between

11 populations of Proechimys, age-class IV (see figures 5-8

for explanation of symbols): 9 mastoidal breadth, 10 rostral

depth, 11 palatal length, 12 alveolar length.

mastoidal (Figure 9) breadths and rostral depth (Figure 10). Maxillary breadth (Figure 6) and alveolar

length (Figure 12) showed little interpopulation

variation.

Student's Mests were run on seven samples of age

class IV (Table 3) and five samples of age class V

(Table 4) to see if the mean differences of condylobasal

length and zygomatic breadth were statistically significant in interpopulation comparisons. The difference

was considered significant when a test of two population means resulted in a low probability value (e.g.,

P<0.05). The Riberalta population (age class IV)

was significantly larger (0.01>P>0.001) in mean condylobasal length than the means of the Puerto Maldonado, San Ignacio Warnes, Limao Balsa, and

Corumba populations. In zygomatic breadth (age class

IV), Riberalta versus San Ignacio was the only highly

significant comparison (0.01 >P).

In means zygomatic breadth (age class V), the San

Ignacio population was significantly smaller (0.02>

P>0.001) than the means of the Riberalta and Puerto

Maldonado populations. Riberalta versus San Ignacio

was the only highly significant (0.1>P>0.05) comparison of condylobasal length (age class V).

Similarities in means cranial dimensions were more

apparent between nearby populations than between

widely separated localities. Clinal variations were not

apparent, but the four southern populations (San

Ignacio, Warnes. Limao Balsa, and Corumba) were

generally smaller in most cranial dimensions, although

these differences were not always statistically

significant.

TEETH.—Although there were wide variations in

tooth counterfold numbers within populations, some

trends were evident. In most populations there were

three counterfolds in the upper cheek teeth, but some

specimens from Hyutanaham and Riberalta had indications of a fourth fold.

Variations in the number of counterfolds in the

TABLE 3.—Values of Student's t and associated probability levels (P) in testing the hypothesis (H:

Xx—X2) of no difference in mean condylobasal length

and zygomatic breadth between two populations, ageclass IV.*

\

VUlMuava

Itbanlta

FMrto

mUonde

Mo

Igmdo

UMrncs

LUio

blM

Cortaba

nllnam

\

(20)

0.102

r».9

(U)

1.407

o.2>r>o.i

<23)

2.323

).02>P>0.01

(20)

0.233

0.9>F>0.»

(19)

0.731

0.5>F>0.4

(It)

1.263

0.3>PX>.2

Utwralta

(U)

2.067

0.05>»X>.02

\

(2*)

1.374

0.2>K-0.1

(29)

3.027

0.01>P>0.001

(29)

0.404

0.7>F>0. 6

(22)

1.381

(23)

0.862

0.4>r>0.3

IMrto

MUnado

(16)

1.100

0. 3>»X>.2

(20)

3.468

o.oi>r«.ooi

\

(27)

1.698

0.2>r>0.1

(24)

1.602

0.2>F>0.1

(20)

0.133

(21)

0.906

0.4>f>0.3

San

Itoclo

(17)

2.601

D.02>r>0.01

(21)

4.930

o.ooi>r

(19)

1.876

0.1>P>O.OS

\

(29)

3.133

D.oi>r>o.oo:

(25)

1.726

(26)

2.379

0.03>p o.o:

(20)

1.187

0.3>r>0.2

(24)

4.930

o.ooi>r

(22)

0.226

0.9>P>0.8

(23)

2.569

o.o2>r>o.oi

\

(22)

1.421

(23)

0.672

0.6>F>0.5

Uaio

» 1 H

(16)

1.510

0.2>F>0.2

(20)

3.800

o.oi>r>o.oo:

(18)

0.363

0.«>F>0.7

(19)

1.130

0.3>P>0.2

(22)

0.949

0.4>f*>.3

\

(19)

0.751

0.4>r>0.3

Conaba

(17)

0.529

0.7>F»O.6

(21)

3.070

o.oi>r>

(19)

0.8O6

0.5>F>0.4

(20)

2.795

D.02>P>0.01

(23)

0.767

0.3>r>0.4

(19)

1.374

0.2>F>0.1

\

rrcauric mu n

•In each rectangle the parenthetic number represents the

degrees of freedom (N\-\-N*—2) in the test; the middle number is the / value; and the bottom numbers represent the

probability of exceeding the observed value of t. The difference was considered significant when a test of two population

means resulted in a low probability value (e.g. P<0.05).
16

TABLE 4.—Value of Student's t and associated probability levels (P) in testing the hypothesis of no difference in mean condylobasal length and zygomatic

breadth between two populations, age-class V. See

Table 3 for explanation of values.

COHKLOBASAL LENGTH

\

Villanueva

Eiber.lt.

Puerto

MaUonado

San

Ignaclo

\

(12)

0.649

0.6>P>0.S

(14)

0.128

fXI.9

(17)

2.005

(U)

0.727

0.5>P>O.4

(11)

0.713

\

(16)

1.036

0.4>P*>.3

(21)

2.661

(16)

0.871

0.4>P>0.3

Maldonado

(11)

0.028

(14)

0.740

0.5>P>0.4

\

(19)

3.212

(14)

1.398

0.2>P>0.1

San

Ignaclo

(11)

0.884

(14)

0.8S9

0.5>P>0.4

(14)

1.770

0.1>P>0.05

\

(19)

1.659

0.2>P>0.1

MIKI

(10)

0.564

(13)

0.540

0.6>P>0.5

(13)

1.430

0.2>P>0.1

(13)

0.499

0.7>P>0.6

ZYGCMATIC BREADTH

lower cheek teeth were more common. In the southern

populations there were either two or three counterfolds,

with a trend toward retention of two folds in ml and

m3. In east-central Bolivia the number varied from two

to three, but ml and m3 usually had three counterfolds.

In northern Bolivia, southeastern Peru, and northwestern Brazil, there were usually three counterfolds,

although some premolars possessed four. Two counterfolds were the rule in the molars of specimens from

Villanueva, Colombia.

Moojen (1948) reported that variation in counterfold number was clinal and the number of folds were

reduced in response to lower humidity. The evidence

from the present study indicates a reduction in the

number of counterfolds in some northern and southern

populations, but no attempt was made to make a correlation with climatic factors.

PELAGE.—A few specimens from each locality were

selected for analyses of pelage characteristics, although

the resulting data were not treated statistically.

No great differences in width of aristiforms were

noted in comparisons of specimens from most populaSMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

tions in Peru, Bolivia, and Brazil. Wide aristiforms

(0.8-1.0 mm) were found on specimens from Porto

Velho. In most other populations, the aristiforms were

narrow (0.3-0.5 mm) or of medium width (0.5-0.8

mm). Aristiforms were long (18-24 mm) in most

populations but short (15-18 mm) examples were

found in some populations in northern Bolivia and

northwestern Brazil.

Conclusions

This study on cranial and bacular variation in Proechimys has led to several conclusions which should

be of use in future studies of this genus.

Eight of ten cranial measurements (condylobasal

length; nasal length; palatal length; zygomatic

breadth; mastoidal breadth; rostral depth; maxillary

breadth; and alveolar length) were found to be statistically significant in showing differences between

populations. The four bacular measurements, however,

were not statistically significant.

Dental wear poses problems in determination of

taxa owing to changing occlusal patterns at different

age levels. Taxonomic assignment can be misleading if

dental patterning is the only criterion used.

Similarities in cranial dimenisons are more apparent

between adjacent than widely separated populations

even though no consistent pattern could be

demonstrated.

Bacula of specimens from any given locality are

usually quite similar in structure although overall dimensions vary.

Most specimens examined are considered to be

Proechimys guyannensis. Specimens from Villanueva,

Colombia are Proechimys canicollis; a single specimen

from Riberalta, Bolivia, represents Proechimys quadruplicates; and specimens from Hyutanaham, Brazil,

are referred to Proechimys steerei, but as additional

knowledge is gained may be found to represent P.

guyannensis.

Several factors should be considered in further

studies of Proechimys. Namely, the range of variation

that was observed in these populations may not be

adequately expressed by subspecific delimitation. In

addition, the specific status of several forms, particularly Proechimys guyannensis and P. longicaudatus,

remains unresolved. Thus, the role of isolating mechanisms, particularly ecological and behavioral, deserves
NUMBER 35 17

more careful consideration. Studies, both observational

and experimental, that consider these factors will contribute greatly to our understanding of speciation in

Proechimys.

Literature Cited

Allen, J. A.

1894. Cranial Variations in Neotoma micropus Due to

Growth and Individual Variation. Bulletin of the

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1899b. The Generic Names Echimys and Loncheres. Bulletin of the American Museum of Natural History,

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Marta, Colombia, Collected by Mr. Herbert H.

Smith, with Field Notes by Mr. Smith. Bulletin

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Burt, W. H., and F. S. Barkalow, Jr.

1942. A Comparative Study of the Bacula of Woodrats

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Cabrera, Angel

1961. Catalogo de los Mamiferos de America del Sur.

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Dice, Lee R.

1932. Variation in a Geographic Race of the Deer

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Ellerman, J. R.

1940. The Families and Genera of Living Rodents.

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Friley, Charles E., Jr.

1947. Preparation and Preservation of the Baculum of

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Goldman, E. A.

1911. Three New Mammals from Central and South

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1961. The Glans Penis in Proechimys and Other Caviomorph Rodents. Occasional Papers, Museum of

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18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Smith, A. C, and I. M. Johnston

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Index

Adelphomyinae, 2

Adelphomys, 2

albispinus, Proechimys, 2

arambourgi, Deseadomys, 2

bolivianus, Proechimys, 10, 11

canicollis, Proechimys, 2-4, 7, 8 (fig.)» 16

cayennensis, Echimys, 2, 4

Proechimys, 2, 4

Dactylomyinae, 2

Deseadomys, 2

arambourgi, 2

loomisi, 2

dimidiatus, Proechimys, 2

Echimyidae, 1-3

Echimyinae, 2

Echimys, 2, 4

cayennensis, 2, 5

myosurus, 5

setosus, 4

trinitatis, 2

goeldii, Proechimys, 3, 8

guyannensis, Mus, 2

Proechimys, 2-3, 5 (fig.), 6, 7, 8 (fig.), 9-14, 16

hendeei, Proechimys, 2, 3, 11

Heteropsomyinae, 2

Hoplomys, 2, 5

iheringi, Proechimys, 2

leucomystax, Proechimys, 11

longicaudatus, Proechimys, 3, 11, 13, 16

loomisi, Deseadomys, 2

Mesomys, 2

micropus, Neotoma, 4

mincae, Proechimys, 7

Mus guyannensis, 2

Myocastorinae, 2

myosurus, Echimys, 4

Trinomys, 4

Neotoma micropus, 5

Paradelphomys, 2

Peromyscus, 5

Proechimys, 1-3, 5 (fig.), 7, 8 (fig.), 9-17

albispinus, 2

bolivianus, 10, 11

canicollis, 2-4, 7, 8 (fig.), 16

cayennensis, 2, 4

dimidiatus, 2

goeldii, 3, 8

guyannensis, 2-3,4 (fig.), 6, 7, 8 (fig.), 9-14, 16

hendeei, 2, 3, 11

iheringi, 2

leucomystax, 11

longicaudatus, 3, 11, 13, 16

mincae, 7

quadruplicates, 3, 10, 16

rattinus, 2

securus, 12

semispinosus, 3

setosus, 2, 4

steerei, 3, 8, 9, 10, 16

trinitatis, 2

vacillator, 2

quadruplicatus, Proechimys, 3, 10, 16

rattinus, Proechimys, 2

securus, Proechimys, 12

semispinosus, Proechimys, 3

setosus, Echimys, 4

Proechimys, 2, 4

Trinomys, 2, 4

steerei, Proechimys, 3, 8, 9, 16

trinitatis, Echimys, 2

Proechimys, 2

Trinomys, 2, 4, 8

myosurus, 4

setosus, 2, 4

vacillator, Proechimys, 2

Xylechimys, 2

19

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V/z" top and left margins, submitted in ribbon copy with a carbon or duplicate, and accompanied

by the original artwork. Duplicate copies of all material, including illustrations, should be retained

by the author. There may be several paragraphs to a page, but each page should begin with a new

paragraph. Number consecutively all pages, including title page, abstract, text, literature cited,

legends, and tables. The minimum length is 30 pages of typescript and illustrations.

The title should be complete and clear for easy indexing by abstracting services. Taxonomic

titles will carry a final line indicating the higher categories to which the taxon is referable:

"(Hymenoptera: Sphecidae)." Include an abstract as an introductory part of the text. Identify

the author on the first page of text with an unnumbered footnote that includes his professional

mailing address. A table of contents is optional. An index, if required, may be supplied by the

author when he returns page proof.

Two headings are used: (1) text heads (boldface in print) for major sections and chapters

and (2) paragraph sideheads (caps and small caps in print) for subdivisions. Further headings

may be worked out with the editor.

In taxonomic keys, number only the first item of each couplet; if there is only one couplet,

omit the number. For easy reference, number also the taxa and their corresponding headings

throughout the text; do not incorporate page references in the key.

In synonymy, use the short form (taxon, author, date, page) with a full reference at the end

of the paper under "Literature Cited." Begin each taxon at the left margin with subsequent lines

indented about three spaces. Within a taxon, use a period-dash (.—) to separate each reference.

Enclose with square brackets any annotation in or at the end of the taxon. For references within

the text, use the author-date system: "(Jones, 1910)" or "Jones (1910)." If the reference is

expanded, abbreviate the data: "Jones (1910, p. 122, pi. 20: fig. 1)."

Simple tabulations in the text (e.g., columns of data) may carry headings or not, but they

should not contain rules. Formal tables must be submitted as pages separate from the text, and

each table, no matter how large, should be pasted up as a single sheet of copy.

For measurements and weights, use the metric system instead of (or in addition to) the

English system.

Illustrations (line drawings, maps, photographs, shaded drawings) can be intermixed

throughout the printed text. They will be termed Figures and should be numbered consecutively;

however, if a group of figures is treated as a single figure, the individual components should be

indicated by lowercase italic letters on the illustration, in the legend, and in text references:

"Figure 96." If illustrations (usually tone photographs) are printed separately from the text as

full pages on a different stock of paper, they will be termed Plates, and individual components

should be lettered (Plate 96) but may be numbered (Plate 9: figure 2). Never combine the

numbering system of text illustrations with that of plate illustrations. Submit all legends on pages

separate from the text and not attached to the artwork.

In the bibliography (usually called "Literature Cited"), spell out book, journal, and article

titles, using initial caps with all words except minor terms such as "and, of, the." (For capitalization of titles in foreign languages, follow the national practice of each language.) Underscore

(for italics) book and journal titles. Use the colon-parentheses system for volume, number, and

page citations: "10(2) :5-9." Spell out such words as "figures" and "plates" (or "pages" when

used alone).

For free copies of his own paper, a Smithsonian author should indicate his requirements on

"Form 36" (submitted to the Press with the manuscript). A non-Smithsonian author will receive

50 free copies; order forms for quantities above this amount with instructions for payment will be

supplied when page proof is forwarded.