PLEISTOCENE MAMMALS FROM EL TAJO QUARRY, STATE OF MEXICO, MEXICO

El Tajo Quarry is a fissure-fill vertebrate fossil site located between El Tajo and Tequixquiac, ~48 km north of Mexico City, Mexico. Fossils were collected from breccia deposits in fissures at a limestone quarry. The deposits are characterized by a light gray color, with angular limestone rock fragments and occasional gravel in a “limy earth matrix” (Furlong, 1925). The quarry’s Cretaceous limestone and Pleistocene fissure deposits are unconformably overlain by horizontal fluvial beds of the fossiliferous late Pleistocene Becerra Formation. Specimens are curated in the University of California Museum of Paleontology at Berkeley (UCMP), locality V2501. Furlong (1925) first reported the El Tajo Quarry fauna when describing a new species of antilocaprid, Capromeryx mexicana. Other than citing a list of taxa in association with the Capromeryx specimens, the fauna has not been well described, other than a report of Microtus from the site (Repenning 1983). The fauna consists of Capromeryx mexicana (UCMP 26648 (holotype) adult skull and postcrania; UCMP 26649 (paratype) juvenile partial skull and limb elements), Platygonus (UCMP 27651 left dentary with teeth), Equus (UCMP 26658 upper molariform), Microtus meadensis (UCMP 27656 left dentary with teeth), Canis latrans (UCMP 26651 partial skull and limb elements), Canis dirus (UCMP 26650 skull and postcrania). Of particular interest is the male dire wolf (Canis dirus) (UCMP 26650), since few associated skeletons of this taxon are known. The skull, partial vertebral column, ribs, partial scapulae, humeri, ulnae, radii, pelvis, femora, tibiae, and various foot elements (carpals, metacarpals, tarsals, metatarsals, phalanges), and proximal half of the baculum are preserved. UCMP 26650 represents an individual intermediate in limb length between the means of the two dire wolf subspecies recognized by Kurten (1984); Canis dirus dirus and Canis dirus guildayi. While El Tajo Quarry has been regarded as Rancholabrean in age (Furlong, 1925; Repenning, 1983), the presence of Microtus meadensis, a mid to late Irvingtonian indicator taxon, raises the question as to whether the fissure-fill deposits are older, perhaps Irvingtonian in age, rather than the vole representing a relict population of Rancholabrean age Microtus meadensis, as Repenning (1983) postulates.