LATE PLEISTOCENE (RANCHOLABREAN) MAMMALIAN FAUNA FROM ZUNI PUEBLO, MCKINLEY COUNTY, NORTHWESTERN NEW MEXICO

Pleistocene mammals are known from two fossil localities on the Zuni Pueblo in McKinley County, northwestern New Mexico, Black Rock and Trapped Rock Draw. The mammalian fauna from the Black Rock site consists of the beaver Castor canadensis, the horse Equus sp., an unidentified camelid, the woodland muskox Bootherium bombifrons, Bison sp. and the Columbian mammoth Mammuthus columbi. The only mammal known from the Trapped Rock Draw site is the American mastodont Mammut americanum. The Black Rock fauna is referred to the Rancholabrean land mammal “age” based on the occurrence of Bison and Bootherium bombifrons, and was derived from sediments that overlay the Black Rock basalt flow which has an Ar/Ar age of 0.164 + 0.035 Ma. The Trapped Rock Draw locality is probably also of late Pleistocene age. Black Rock has a typical assemblage of large grazing mammals found in Pleistocene sites throughout New Mexico, including Equus, camel, Bison, and Mammuthus; however, two other species from this fauna, Bootherium bombifrons and Castor canadensis, are absent from late Pleistocene faunas elsewhere in the state. Mammut americanum is rare in the desert southwest. An American mastodont jaw from Trapped Rock Draw represents the sixth record of this species from the Pleistocene of New Mexico. The beaver, woodland muskox, and American mastodont suggest the presence of both permanent water and forests in the vicinity of Zuni Pueblo during the late Pleistocene, whereas the rest of the mammalian fauna is indicative of grassland or savanna habitats. The ancestral Zuni River apparently was a fairly large permanent stream that supported a diverse riparian forest.