DETERMINING SPECIES OF EQUUS FROM THE MID IRVINGTONIAN FAIRMEAD LANDFILL LOCALITY, MADERA COUNTY, CALIFORNIA

The mid Irvingtonian age (0.78 Ma to 0.55 Ma) Fairmead Landfill site in Madera County, California preserves a diverse fauna collected from fluvial channel, overbank, and lacustrine deposits of the upper unit of the Turlock Lake Formation. The fauna is dominated by large herbivorous mammals, with Equus representing nearly two-thirds of identified specimens. The horses include individuals of all ontogenetic ages, from juveniles to aged adults. The Fairmead Landfill collection provides ample material for comparison to other Pleistocene horses throughout North America. Metatarsals from the Fairmead Landfill were measured and compared to Equus from the following sites: Equus sp., Irvington, California; E. “occidentalis”, McKittrick and Rancho La Brea, California; E. scotti, Rock Creek, Texas; Equus sp., Dalhart Horse Quarry, Texas; E. conversidens, San Josecito Cave, Mexico; E. ferus, Natural Trap Cave, Wyoming; and Equus sp., Natural Trap Cave, Wyoming. Horses from Fairmead Landfill fall in the low end of the E. “occidentalis”/ E. scotti distribution and in the upper end of the E. conversidens / E. ferus range. In addition to postcranial metrics, mandibles were examined for the presence or absence of infundibula, a character useful in distinguishing among horse species. The presence of infundibula in lower incisors of Equus at Fairmead Landfill indicates that these horses are neither E. “occidentalis” nor E. conversidens, since both these species lack infundibula in the lower incisors. This suggests the horse species from Fairmead Landfill may be either E. scotti or E. ferus, both of which possess infundibula. The infundibulum of the right 3rd incisor is open posteriorly, which also occurs in both E. scotti and Pleistocene North American E. ferus. Additional research is underway, using phalanges, in an attempt to further refine the species determination of Fairmead Landfill Equus specimens.