JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Society of Mammalogists is collaborating with JSTOR to digitize, preserve and extend access to Journal of Mammalogy.ABSTRACT.-An apparent case of sympatry between two supposed races of Alouatta palliata (Gray) was discovered near Macuspana, Tabasco, Mexico. Howler monkeys in the Tabascan series were easily separated into two distinct groups based on various characteristics of the cranium, dentition, and pelage. Further comparisons revealed that these two groups were identifiable as Alouatta palliata mexicana Merriam and Alouatta palliata pigra Lawrence. Several possible interpretations of this situation are discussed and, in view of the observed sympatry and distinctive morphological differences, pigra is elevated to specific status; the systematic status of Alouatta villosa (Gray) also is discussed. Several admittedly speculative explanations are offered to account for the existence of two distinct species of howler monkeys in Middle America.
DESCRIPTION OF THE SAMPLE FROM THE VICINITY OF MACUSPANA, TABASCOAdult males from this locality can be separated easily into two distinct groups based on the size and shape of the skull. One group has small skulls that are proportionately short and broad when compared with the large, but relatively long and narrow, skulls of the second group. Several of the more important cranial differences are given in Table 1.The anterior portion of the zygomatic arch of the large-skulled males slopes outward and rearward at an angle of more than 90 degrees. In the small-skulled individuals, this angle is nearly 90 degrees (Fig. 1). The attachment of the posterior portion of the arch is less abrupt in the large monkeys, that is, it 358 May 1970 SMITH-SYSTEMATIC STATUS OF ALOUATTA PIGRA 359 A B FIG. 1.-Crania of two adult males (KU 66247 and KU 66241, respectively) from 5 mi. SE Macuspana, Tabasco, Mexico, illustrating typical differences in size and shape observed in this series.
Further comparisons revealed (A) to be identical with Alouatta palliata pigra Lawrence, and (B) to be Alouatta palliata mexicana Merriam (see text for discussion). Line between A and B is 30 mm in length.extends along the braincase without a sharp emargination, forms a rather wide mastoidal shelf, and is confluent with the lamboidal crests. In the small crania, the arch attaches abruptly to the braincase and is strongly emarginated anterior to the auditory region (Fig. 1).If the mandible is properly articulated with the cranium, set on a flat, level surface, and viewed from the side, the following differences are readily apparent. In the large crania, as a result of a greater extension and forward pitch of the ascending ramus of the mandible, the supraoccipital region a...
