New Mexico Geological Society Annual Spring Meeting — Abstracts

Fossil vertebrates occur in Quaternary alluvium exposed in commercial sand and gravel pits in the Pecos River Valley about 10 km northeast of Roswell, Chaves County, southeastern New Mexico. Fossils were recovered from at least six localities in section 35, T8S, R25E and sections 3 and 10, T9S, R25E. The fossils come from coarse-grained sandstones and conglomerates mined for gravel and consist of isolated and mostly fragmentary remains of tortoises and large mammals.

The vertebrate fauna is composed offive species, the extant desert tortoise Gopherus cf. G. agassizii and four extinct species of mammals, including the horses Equus occidentalis and a smaller species of Equus, a bison, Bison sp., and the Columbian mammoth, Mammuthus columbi. The desert tortoise, identified from several isolated shell fragments and a complete humerus, no longer inhabits New Mexico, although it is known from at least seven other Pleistocene localities in the southern half ofthe state. This species is currently restricted to the Mojave Desert in southeastern California, southernmost Nevada and Utah, western Arizona, and northern Sonora in Mexico. The presence of G. agassizii in southern New Mexico suggests this region experienced milder winters during certain intervals ofthe Pleistocene. A partial dentary with three teeth and an isolated P2 are referred to the horse Equus occidentalis, whereas several isolated teeth belong to a smaller undetermined species of Equus. An isolated lower molar pertains to a species of Bison, presumably either B. latifrons or B. antiquus; however, the absence of a hom core precludes a more precise identification. The most common member of the fauna, Mammuthus columbi, is represented by one complete M3 and about ten partial molars, several of which reportedly came from a skull that was destroyed during mining operations. The Columbian mammoth is widespread in Rancholabrean faunas throughout New Mexico. These fossil mammals indicate a Rancholabrean age and constitute an assemblage very similar to that from the Edith Formation in the vicinty of Albuquerque in the Rio Grande Valley.