MAMMALIAN SPECIES No. 498, pp. 1-3, 3 figs.

Sciurus oculatus. By Troy L. Best

Published 23 June 1995 by The American Society of Mammalogists

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Sciurus oculatus Peters, 1863 of the forelegs. The outsides of the lower hind legs vary from gray,
as the rest of the thigh, to dark rusty brownish. The underparts
Peters' Squirrel vary from white with pale dull-huffy suffusion to rich ochraceous-
Seiurus oeulatus Peters, 1863:653. Type locality " Mexico," prob- buff. Dorsally, the tail is black and heavily washed with white.
ably near Las Vigas, Veracruz (Nelson, 1899:88). Ventrally, the tail has a broad median area of grizzled yellowish.
Sciurus niger melanonotus Thomas, 1890:73. Type locality "Las gray, bordered with black and heavily edged with white. The hairs
Vigas, Jalapa, " Veracruz, Mexico.
CONTEXT AND CONTENT. Order Rodentia, Suborder
Sciurognathi, Family Sciuridae, Subfamily Sciurinae, Genus Sciurus,
Subgenus Seiurus (Wilson and Reeder, 1993). Based upon structure
of the hyoid bones, S. oeulatus also has been placed into the subgenus
Paraseiurus (Hoffmeister and Hoffmeister, 1991). The genus Sciu -
rus contains 28 species (Wilson and Reeder, 1993). Three subspecies
of S. oeulatus are recognized (Hall, 1981):
S. o. oeulatus Peters, 1863:653, see above (melanonotus Thomas
is a synonym).
S. o. shawi Dalquest, 1950:4. Type locality "Rancho San Francisco,
38 kilometers east-southeast of the City of San Luis Potosi,
San Luis Potosi, Mexico."
S. o. tolueae Nelson, 1898:148. Type locality "north slope of
Volcano of Toluca, Mexico, Mex."
DIAGNOSIS. Seiurus oeulatus may be sympatric with S.
aureogaster and S. deppei (Hall, 1981; Musser, 1968). S. oeulatus
(total length, 530-560 rom) is about the size of S. aureogaster(total
length, 418-573 rom), but S. oeulatus has a stouter body (Dalquest,
1953; Hall, 1981) and does not have a P3. S. deppei (total length,
343-387 mm) has the P3 and is much smaller than S. oculatus .
Superficially S. oeulatus resembles S. carolinensis, especially the
more southern subspecies of S. earolinensis . The most obvious
difference is the absence of P3 in S. oeulatus (Fig. 1). Genetic
relationships may be closer to S. niger than to S. carolinensis (Hall,
1981).
The ranges of S. oeulatus and S. alleni approach each other
in San Luis Potosi, but these taxa are not sympatric (Hall, 1981).
S. oculatus and S. alleni show no marked differences (Baker, 1956;
Dalquest, 1953), but on average S. alleni has a smaller skull, smaller
body, grayer feet, and whiter venter (Nelson, 1899). Compared with
S. alleni, S. oculatus shawi in San Luis Potosi has: buffy, rather
than brownish or whitish feet; distinct, buffy postauricular patches;
deep-huffy underparts rather than white underparts. In S. alleni,
the postauricular patches usually are absent, and when present
usually consist of a tiny area where the pelage is slightly shorter
and grayer than on the surrounding part of the head (Dalquest,
1950). The postauricular patch is prominent and buffy on S. o.
shawi and dirty white on S. o. tolueae (Hall, 1981).
GENERAL CHARACTERS. Peters ' squirrel is a large tree
squirrel (Dalquest, 1953; Nelson, 1899). The upperparts are either
uniform grizzled gray or have a median band or strong suffusion of
black. The ears and orbital ring are dull white to buffy. Dorsally,
the tail is black with a heavy suffusion of white. Ventrally, the tail
is grizzled gray to yellowish brown, with a border of black hairs
tipped with white. The underparts vary from white with pale-yellowish
suffusion to rich ochraceous-buff (Hall, 1981).
In S. o. oeulatus. the crown between the ears and the broad
band along the middle of the back from the shoulders to the base
of the tail are black or blackish, shading on the edges to dark gray
like the remainder of the upperparts. The ring around the eye is
well marked, buffy whitish or buffy. The cheeks usually are grizzled
gray like the sides of the neck, but sometimes are washed with buff.
The ears are dingy gray and frequently washed with dull buff of FIG. 1. Dorsal, ventral, and lateral views of cranium and
variable intensity. The basal ear patch varies from dingy white to lateral view of mandible of Seiurus oculatus from Encarnacion,
dark buffy (sometimes absent in summer). The feet vary from grizzled Hidalgo, Mexico (male, United States National Museum of Natural
gray washed with buffy to rich buff shading to gray on the outside History 81439). Greatest length of cranium is 61.7 mm.
2 MAMMALIAN SPECIES 498

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FIG. 3. Baculum of Seiurus oeulatus from Amoles, Quere-
taro . Mexico (modified from Burt, 1960).

The underparts are dingy whitish. with only a faint suffusion of buffy.
Compared with S. o. oculatu s (Fig. 1). the skull of S. o. tolueae is
similar. but in nearly all individuals the nasals are narrower poste.
riorly with a corresponding increa se in breadth of the premaxillaries.
S. o. tolueae can be distinguished from S. o. oeulatus by the whitish
ear patche s and whitish ventral surface in S. o. tolueae (Nelson,
1899). S. o. shawi differs from S . o. oeulatus in lacking the stripe
along the back. This stripe always is present in S. o. oeulat us, but
varies from a deep black band to a blackish wash. In S. o. shaioi,
FIG. 2. Distribution of Seiu rus oeulatus in Mexico (Hall,
there is no trace of a dark wash on the back. From S. o. tolueae,
1981 ): 1, S. o. oculatus; 2, S. o. shawi ; 3, S. o. tolueae. S. o. sha wi differs, as it does from S. o. oeulatus, in lacking the
blackish dorsal stripe. and in addition S. o. shawi is rich buff rather
than whitish beneath (Dalquest, 1950).
of the back are black. with one or two rings of gray. yellowish gray, Averages of external and cranial measurements (in mm) of S.
or brownish gray. mixed with other hairs that are wholly black o. oculatus, S. o. shaioi, and S. o. tolueae, respectively. are: total
(Nelson. 1899). length. 543, 508 , 531 ; length of tail. 269 , 256, 263; length of
In S. o. shawi, the upperparts are pale gray . and the underpart s hind foot. 73, 68 . 69; basilar length of cranium, 54 .6, 55.9, 54.0;
are pale buff. The nose and face are grizzled, the eye ring is warm palatal length, 28.5 , ...• 29.0; interorbital breadth, 20.3, 20.2 , 20.5;
buff, and the top of the head is near hair brown mixed with cinnamon. zygomatic breadth , 36.3. 36.5, 36. 7; length of upper toothrow,
The upperparts are mixed black and avellaneous, resulting in a 11.0 . 11.2 , 11.0 (Dalquest, 1953; Nelson, 1899 ).
general color of drab or buffy brown. The sides are more whitish
and less black than the back. The postauricular spots are near pinkish DISTRIBUTION. Sciurus oculatus is endemic within the
buff. The underparts are pinkish cinnamon. The tops of the feet are Trans-Mexican neovolcanic belt (Fa and Morales. 1991), and it
cinnamon. The top of the tail is white with black underfur showing ranges over the Mexican Plateau from the Mexican states of Morelos,
through where disarr anged. The underside of the tail is tricolored; Distrito Federal. Mexico. Puebla, and Veracruz northward into San
the central area of the tail is 35 mm wide and drab. the intermediate Luis Potosi (Fig. 2; Dalquest, 195 3; Hall. 1981 ). Peters' squirrel
area is 8 mm wide and black, and the edge is 10 mm wide and occupies oak (Quercus ). pine (Pinus ), and fir (Abies, Pseudotsuga)
white. Variations are slight. but postauricula r spots may be reduced forests in the lower Sonoran, upper Sonoran, transition, Canadian.
in some individuals. and the middorsal area may be slightly darker and Hudsonian life zones at elevations of 1,500-3.600 m (Goldman,
in some individuals than in others (Dalquest, 1953) . 1951; Hall. 1981; Nelson, 1899).
In S. o. tolueae, the top of the head and the broad median FOSSIL RECORD. The genus Seiurus evolved by the early
line down the back to the base of the tail are gray with a faint Miocene (Black. 1972). No fossils of S. oeulatus are known.
blackish or dull brownish wash shading laterally into clearer grizzled.
gray. However, the grizzled gray has slight shading of yellowish on FORM AND FUNCTION . The dental formula is i 1/ 1, c
the subterminal rings of some hairs. The ring around the eye is 0/ 0, P 1/1. m 3/3, total 20 (Hall. 198 1). The hyoid apparatus
grayish white with a pale-buffy shade. The rest of the sides of the consists of a single basihyal and paired thyroh yals, ceratohyals, and
head are dingy gray suffused with dull buffy or pale brownish. The stylohyals; the basihyal is thick. triangular in cross-section, long,
ears are dull gray shaded with buff. The patch behind the ear is and fuses with the short thyrohyals at an early age (Hoffmeister and
dingy white. The feet are grayish white with a buffy wash that is Hoffmeister . 1991 ).
deeper than on the underparts. The thighs near the feet are suffused The pelage is dense and rath er coarse. The hair of the middorsal
with yellowish brown. Dorsally, the tail is black and heavily washed area is 15 mm long. hair of the middle of the tail is 58 mm long.
with white. Ventrally. the tail along a median line is grizzledyellowish. and near the tip of the tail the hair is 80 mm long (Dalquest, 1953).
gray or pale yellowish-brown, bordered with black and broadly edged The underfur is long. and the tail is long and full. The four pair of
with white. The hairs of the back are black with one or two rings mammae are arranged as follows: one pectoral; two abdominal; one
of gray. yellowish. or brownish gray. mixed with other hairs that inguinal (Nelson, 1899).
are wholly black (Nelson, 1899 ). The baculum of S. oculatus (Fig. 3) is most like bacula of S.
There is relatively little variation within subspecies. In S. o. arizonensis, S. carolinensis, and S. niger. The basal portion of the
oculatus, the black dorsal band usually is present . sometimes is shaft is circular or nearly so in cross section. The shaft tapers distally.
continuous from the crown to the tail. and is 25-50 mm in width. with an apparent twist. to its smallest diameter. which is called the
However, the black dorsal band also may be represented only by a neck. At this point the shaft usually curves dorsally and expands
black wash. The buff of the underparts of some individuals is richer into a broad circular disc that is concave on the right side and convex
than that in others. The intensity of the buff of the feet accompanies on the left. Ventral to this expanded disc is a definite spur. In S.
and varies with the same color on the underparts. One melanistic oculatus, the shaft tapers to a narrow neck. just proximal to the
specimen is known from Pinal de Amoles, Queretaro. Color of S. o. expanded distal end, and the spur is blunt instead of coming to a
tolueae varies little. and this mainly is in the amount of buffy on point as in the other squirrels. The posterior part of the disc ends
the feet and in the intensity of the dark wash along the middle of in a definite point and is shaped like a hook. There is a prominent
the back . One melanistic specimen is known from the type locality dorsal keel on the shaft. Measurements of two bacula from Queretaro
(Nelson, 1899) . are: length, 10.8. 11.5; length of expanded tip, 2.7, 3.0 ; height of
Compared with S. o. oculatus, S. o. tolueae is paler, with a tip. 3.2. 3.2; height of base, 2.5. 2.8; width of base, 1.9. 2.1 (Burt,
wash of blackish or blackish brown along the middle of the back. 1960).
MAMMALIAN SPECIES 498 3

ONTOGENY AND REPRODUCTION. In Veracruz, fe- CEBALLOS, G., AND P. RODRIGUEZ. 1993. Diversidad y conser-
males in July and August had enlarged mammae, indicating an earlier vacion de los mamiferos de Mexico: II. Patrones de endemi-
litter of young, but no young-of-the-year were observed. No pregnant cidad. Pp, 87-108, in Avances en el studio de los mamiferos
females were observed 26 July-4 August (Davis, 1944). de Mexico (R. Medellin and G. Ceballos, eds.), Publicaciones
Especiales, Asociacion Mexicana de Mastozoologia, 1:1-464.
ECOLOGY AND DEHAVIOR. Sciurus oculatus occurs in DALQUEST, W. W. 1950. Records of mammals from the Mexican
the pine and oak forests of the tableland slope of the Sierra Madre state of San Luis Potosi. Occasional Papers of the Museum of
Oriental and the arid mountains of southern and western Queretaro, Zoology, Louisiana State University, 23: 1-15.
central and eastern Guanajuato, and southern San Luis Potosi (Nel- . 1953. Mammals of the Mexican state of San Luis Potosi.

Downloaded from https://academic.oup.com/mspecies/article/doi/10.1644/0.498.1/2600154 by Weil, Gotshal, & Manges user on 27 November 2023
son, 1899). In San Luis Potosi, S. oculatus lives in oak woods on Louisiana State University Press, Baton Rouge, 229 pp.
the mountains of the Mexican Plateau, exclusive of the crest of the DAVIS, W. B. 1944. Notes on Mexican mammals. Journal of
Sierra Madre. Peters' squirrel is common in summer in the vicinity Mammalogy, 25:370-403.
of Alvarez, where it lives in the low oak forest on the mountainsides. FA, J. E., AND L. M. MORALES. 1991. Mammals and protected
However, S. oculatus was not present there in late October, after areas in the Trans-Mexican neovolcanic belt. Pp. 199-226,
the weather had turned cold. Some were observed in deep arroyos in Latin American mammalogy: history, biodiversity, and con-
in nearby valleys where they were feeding on almonds (Prunus) and servation (M. A. Mares and D. J. Schmidly, eds.). University
were secretive. They moved swiftly through the trees and easily of Oklahoma Press, Norman, 468 pp.
crossed gaps of ~2 m (Dalquest, 1953). At Villar, San Luis Potosi, FERRIS, G. F. 1951. The sucking lice. Memoirs of the Pacific
near the northern border of its range, S. oculatus occurs in the Coast Entomological Society, 1:1-320.
oaks of the upper and lower Sonoran zones (1,650-1,800 m elev.) GOLDMAN, E. A. 1951. Biologicalinvestigations in Mexico. Smith-
where it feeds on acorns and wild figs (Ficus) in the canyon bottoms. sonian Miscellaneous Collections, 115: 1-476.
Its main food supply, however, is obtained from various species of HALL, E. R. 1981. The mammals of North America. Second ed.
pines (Nelson, 1899). In Veracruz, S. oculatus occupies pine forests John Wiley and Sons, New York, 1:1-600 + 90.
at the higher elevations. On the timbered slopes of Cofre de Perote HOFFMEISTER, R. G., AND D. F. HOFFMEISTER. 1991. The hyoid
and Mount Orizaba, this is the common squirrel (Davis, 1944). in North American squirrels, Sciuridae, with remarks on as-
The only ectoparasites known from Peters' squirrel are the lice sociated musculature. Anales del Instituto de Biologica, Univ-
Enderleinellus longiceps (Ferris, 1951) and E. oculatus (Kim, ersidad Nacional Autonoma de Mexico, Serie Zoologia, 62:
1966). No endoparasites are known. 219-234.
Sciurus oculatus is considered to be a "fragile" species (Ce- JAEGER, E. C. 1955. A source-book of biological names and terms.
ballos and Navarro L., 1991; Ceballos and Rodriguez, 1993). It has Third ed. Charles C Thomas Publisher, Springfield, Illinois,
suffered severe habitat loss through logging, burning, and clearing 323 pp.
of forests for agriculture (Leopold, 1959; Nowak, 1991). KIM, K. C. 1966. The species of Enderleinellus (Anoplura, Ho-
plopleuridae) parasitic on the Sciurini and Tamiasciurini. The
REMARKS. Sciurus oculatus is similar to S. alleni (Nelson, Journal of Parasitology, 52:988-1024.
1899), and S. alleni has been considered to be a subspecies of S. LEOPOLD, A. S. 1959. Wildlife of Mexico: the game birds and
oculatus (Moore, 1960). Squirrels ancestral to S. alleni, S. nay- mammals. University of California Press, Berkeley, 568 pp.
aritensis, and S. oculatus may have spread from western Mexico MOORE, J. C. 1960. The relationships of the gray squirrel, Sciurus
across the Mesa del Norte by way of mountains in western Coahuila, carolinensis, to its nearest relatives. Proceedings of the Annual
Durango, and Zacatecas (Baker, 1956). Nothing is known concern- Conference of the Southeastern Association of Game and Fish
ing the genetics of S. oculatus. Commissioners, 13:356-363.
Sciurus is from the Latin sciurus meaning squirrel. The specific MUSSER, G. G. 1968. A systematic study of the Mexican and
epithet oculatus is derived from the Latin oculus referring to the Guatemalan gray squirrel, Sciurus aureogaster F. Cuvier (Ro-
eye (Jaeger, 1955). S. oculatus also has been referred to as the dentia: Sciuridae). Miscellaneous Publications of the Museum
black-backed (Nelson, 1899), Toluca (Nelson, 1898), and spectacled of Zoology, University of Michigan, 137: 1-112.
squirrel (Dalquest, 1950). NELSON, E. W. 1898. Descriptions of new squirrels from Mexico
I thank L. L. Thornton, A. M. Coffman, and other personnel and Central America. Proceedings of the Biological Society of
in the Interlibrary Loan Department at Auburn University R. B. Washington, 12:145-156.
Draughon Library for assistance in obtaining articles from other . 1899. Revision of the squirrels of Mexico and Central
institutions, T. D. Haas for help in locating literature, J. Birch for America. Proceedings of the Washington Academy of Sciences,
providing locality data for Fig. 3, W. B. Robinson for helping in the 1:15-110.
preparation of Fig. 1, and T. Rodriguez for preparing Fig. 2. R. NOWAK, R. M. 1991. Walker's mammals of the world. Fifth ed.
Dowler, G. W. Folkerts, M. T. Mendonca, and E. C. Oaks critically The Johns Hopkins University Press, Baltimore, Maryland,
evaluated an early draft of the manuscript. This is journal article 1:1-642.
no. 15-933621 of the Alabama Agricultural Experiment Station. PETERS, W. 1863. Machte eine Mittheilung iiber neue Eichhor-
narten aus Mexico, Costa Rica und Guiana, so wie iiber Scalops
LITERATURE CITED latimanus Bachmann. Monatsberichte der Preussische Aka-
demie der Wissenschaften zu Berlin, pp. 652-656.
BAKER, R. H. 1956. Mammals of Coahuila, Mexico. University THOMAS, O. 1890. On a collection of mammals from central Vera
of Kansas Publications, Museum of Natural History, 9:125- Cruz, Mexico. Proceedings of the Zoological Society of London
335. for 1890:71-76.
BLACK, C. C. 1972. Holarctic evolution and dispersal of squirrels WILSON, D. E., AND D. M. REEDER (EDS.). 1993. Mammal species
(Rodentia: Sciuridae). Evolutionary Biology, 6:305-322. of the world: a taxonomic and geographic reference. Second
BURT, W. H. 1960. Bacula of North American mammals. Mis- ed. Smithsonian Institution Press, Washington, D.C., 1206 pp.
cellaneous Publications of the Museum of Zoology, University
of Michigan, 113: 1-76.
Editors of this account were ELAINE ANDERSON, J. ALDEN LACKEY,
CEBALLOS, G., AND D. NAVARRO L. 1991. Diversity and conser-
and KARL F. KOOPMAN. Managing editor was JOSEPH F. MERRITI.
vation of Mexican mammals. Pp. 167-198, in Latin American
mammalogy: history, biodiversity, and conservation (M. A. T. L. BEST, DEPARTMENT OF ZOOLOGY AND WILDUFE ScIENCE AND
Mares and D. J. Schmidly, eds.). University of Oklahoma Press, ALABAMA AGRICULTURAL EXPERIMENT STATION, 331 FUNCHESS HALL,
Norman, 468 pp. AUBURN UNIVERSITY, ALABAMA 36849-5414.