The Subspecies of the Mexican Red-bellied
Squirrel, Sciurus aureogaster

BY

KEITH R. KELSON

University of Kansas Publications
Museum of Natural History
Volume 5, No. 17, pp. 243-250
April 10, 1952

University of Kansas
LAWRENCE
1952

University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Edward H. Taylor, Robert W. Wilson

Volume 5, No. 17, pp. 243-250
April 10, 1952


University of Kansas
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1952

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[Pg 245]

The Subspecies of the Mexican Red-bellied
Squirrel, Sciurus aureogaster

BY

KEITH R. KELSON

In his excellent taxonomic treatment of the tree squirrels of Mexico and Central America, Nelson (Proc. Washington Acad. Sci., 1:15-110, 2 pls., May 9, 1899) recognized three subspecies of red-bellied squirrels, Sciurus aureogaster aureogaster F. Cuvier, Sciurus aureogaster hypopyrrhus Wagler, and Sciurus aureogaster frumentor Nelson. In his lists of specimens examined, Nelson (op. cit.:42 and 44) assigned certain specimens from "mountains near Santo Domingo" and Guichicovi in Chiapas, and Catemaco in Veracruz, to S. a. aureogaster, and other specimens from the same localities to S. a. hypopyrrhus. I originally attempted to study (identify to subspecies) the series of animals from only three places, but it became evident that a more extensive study was indicated.

The locality whence the holotype of Sciurus aureogaster aureogaster was obtained is unknown. Because certain specimens from Altamira, Tamaulipas, closely resemble Cuvier's figure of the type, Nelson (op. cit.:41) subsequently designated Altamira as the type locality. Miniatitlan, Veracruz, was designated by Nelson as the type locality of S. a. hypopyrrhus because Wagler's description of the type of that subspecies fitted so well certain of Nelson's specimens from that place.

Sciurus a. hypopyrrhus was said by Nelson (op. cit.:43 and 44) to differ from S. a. aureogaster in darker color, thinner pelage, much stiffer and more shining dorsal hairs, slenderer tail with black predominating, larger and proportionately narrower skull with larger auditory bullae, each bulla being "slightly constricted just in front of middle." Sciurus aureogaster varies greatly in intensity of color and in color-pattern. Fully 30 per cent of the specimens examined are in some degree melanistic and approximately 20 per cent of them are completely so. Others are more or less brown; the brown dulls the usually rufous parts. In many specimens this brown is well distributed even in the otherwise grizzled areas; in some specimens it is evenly distributed and in others it is in patches. Indeed, scarcely any two "normally" colored specimens are alike. Typically, the intense rufous color characteristic of the underparts in both [Pg 246] S. a. aureogaster and S. a. hypopyrrhus is also present on the costal region and shoulders. Even this distribution of color is highly variable; some specimens (for example No. 23948 KU, from 3 km. E San Andres Tuxtla, Veracruz) show no rufous dorsally and others (for example No. 19307 KU, from 20 km. W Piedras Negras, Veracruz) have the rufous extending over the legs, sides, and almost all of the dorsum from the shoulders to the rump except (in some) for an interrupted median strip of grizzled gray. It is true that specimens from Miniatitlan are darker than those from Altamira, but this seems not to be significant taxonomically, because examination of series from other localities provides no evidence of geographic variation in color except, possibly, in the frequency of melanism. A series of 13 specimens (Univ. Kansas) from 7 and 8 km. WNW Potrero, Veracruz, for example, is quite as dark as topotypes of S. a. hypopyrrhus from Miniatitlan, although the localities of capture are approximately in the center of the geographic range of S. a. aureogaster. In short, there seems to be no way to distinguish S. a. hypopyrrhus from S. a. aureogaster on the basis of color. An unusual amount of variation exists, but it seems to occur at random. Fixing type localities of the two subspecies at the places of origin of certain specimens which in color fit the original descriptions is meaningless because selected specimens or series from almost any place in the geographic range of the species would qualify as approximate color-duplicates of the types.

My findings agree with those of Nelson in that skulls from Miniatitlan average longer and narrower than those from Altamira, but this seems not to be significant taxonomically because the series from Altamira is, to judge from the material I have seen, somewhat shorter and broader cranially than is "average" for the alleged subspecies S. a. aureogaster. For example, series from Metlaltoyuca in Puebla, 3 km. E Axtla in San Luis Potosí, 8 km. NW Potrero and 20 km. NW Piedras Negras in Veracruz, although obtained from localities well within the geographic range of S. a. aureogaster (as outlined by Nelson), all more closely resemble the "topotypes" of S. a. hypopyrrhus in cranial measurements than they do "topotypes" of S. a. aureogaster. Conversely, specimens from that part of the range of S. a. hypopyrrhus most remote from the range of S. a. aureogaster (Montecristo, La Venta, and Teapa, all in Tabasco) more closely approximate the Altamiran series in cranial size and proportions than they do the Miniatitlan material. Therefore, my data contradict the statement of Nelson (loc. cit.) that the skulls of S. a. hypopyrrhus are larger but proportionately narrower than those [Pg 247] of S. a. aureogaster. The constriction of the auditory bullae alluded to by Nelson as being present in S. a. hypopyrrhus is also present in S. a. aureogaster, occurring in both subspecies in varying degrees without correlation with geographic distribution.

Actually, the only concrete evidence of geographic variation that I can detect in these animals is a slight increase southwardly in the frequency and degree of melanism, a kind of variation that is unworthy of taxonomic recognition in this species. It seems best, then, to regard the name Sciurus aureogaster hypopyrrhus Wagler as a synonym of Sciurus aureogaster aureogaster F. Cuvier.

Nelson (op. cit.:45) stated that S. a. frumentor "Differs strikingly from typical aureogaster in having well-marked nuchal and rump patches of yellowish brown or rufous brown; the underparts gray or gray washed with rufous; tail heavier and more bushy; pelage softer.... Skull indistinguishable from that of typical aureogaster." I have examined 22 specimens from Jico, 7 from Las Vigas (the type locality), and one from 3 km. E Las Vigas, all in Veracruz. These include the type and paratypes of S. a. frumentor. Part (probably 7 specimens) of the series from Jico was referred by Nelson (op. cit.:46) to S. a. frumentor and he thought, or knew, these specimens to have been taken above Jico. The remaining specimens labelled as from Jico were referred to S. a. aureogaster. I am unable to find fault with the characterization of S. a. frumentor insofar as color or skull are concerned. I cannot verify to my own satisfaction the presence of "heavier" and bushier tail and softer pelage. The characters considered to be diagnostic of S. a. frumentor are distributed in an interesting geographic pattern the genetic import of which is not wholly clear. One specimen (No. 23945 KU) of the two available from 3 km. SW San Marcos, Veracruz, a locality on the coast approximately 50 miles north of Las Vigas, is indistinguishable from topotypes of S. a. frumentor except for slightly lighter-colored grizzled parts. The second specimen (No. 23946 KU) from the same locality, although a subadult in worn pelage, shows the color and striking dorsal pattern of S. a. frumentor and the ventral color of S. a. aureogaster. The dorsal pattern of S. a. frumentor is found also in the three specimens from San Carlos and Plan del Río, Veracruz (Nos. 11082, 11083 and 8278), Chicago Nat. Hist. Mus., respectively. (The two specimens from San Carlos were referred to S. a. frumentor by Elliot, Field Columb. Mus., Zool. Ser., vol. 8, Publ. no. 115:128, February 9, 1907.) Nevertheless, although the essential morphological characters of S. a. frumentor occur sporadically in other populations, the [Pg 248] animals from the higher elevations above Jico and Las Vigas are notably homogeneous, differ collectively from surrounding populations, and occupy a logical geographic range. Therefore S. a. frumentor is retained as a tenable subspecies, and the animals from the vicinity of San Marcos, and from San Carlos and Plan del Río are referred to S. a. aureogaster. Incidentally, Nelson (op. cit.:45) remarks that he saw no melanistic specimens of S. a. frumentor. This is not strange because melanistic specimens could not be identified anyway.

Fig. 1. Geographic distribution of Sciurus aureogaster.
1. Sciurus aureogaster aureogaster.       2. Sciurus aureogaster frumentor.

[Pg 249] The names, absolute synonyms, and geographic ranges of the two subspecies of Sciurus aureogaster here recognized are as follows:

This report is based on the examination of 256 specimens representing the entire known geographic range of the species. I am indebted to H. E. Anthony, Remington Kellogg, C. C. Sanborn, and Stanley P. Young for the privilege of examining specimens in their charge. The study here reported upon was aided by a contract between the Office of Naval Research, department of the Navy, and [Pg 250] the University of Kansas (NR 161-791). The specimens in the University of Kansas Museum of Natural History were obtained by field work supported by the Kansas University Endowment Association.

Transmitted December 6, 1951.

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