THE SMALL MAMMAL FAUNA FROM THE PLEISTOCENE HARVESTON LOCALITY, RIVERSIDE COUNTY, CALIFORNIA

A mitigation project conducted in 2003 during construction of the Harveston subdivision in Temecula, southwestern Riverside County, California, recovered numerous fossil vertebrates. Material was recovered from two units: the Irvingtonian Pauba Formation and an overlying unnamed Rancholabrean unit (based on the presence of Bison antiquus). Preliminary examination of the microvertebrate sample from the Pauba Fm. has resulted in the identification of the genera Microtus (43% of identified small mammal fauna), Thomomys (30%), Neotoma (11%), Dipodomys (6%), Peromyscus (6%), Onychomys (2%), and Sylvilagus (2%). The overlying Rancholabrean unit has produced Thomomys (75%) and Neotoma (25%), but is based on only four identified specimens. While the sample size is small, the Rancholabrean fauna is similar to the Thomomys- and Neotoma-dominated microvertebrate fauna from Diamond Valley Lake, located only 10 km away. Thomomys and Neotoma are generally associated with more arid and open habitats. This is consistent with the large mammal fauna recovered from the Rancholabrean unit at Harveston, which includes Equus, Bison, Mammuthus, Hemiauchenia, and cf. Antilocapra. The shift from a Microtus-dominated fauna in the Irvingtonian to a Thomomys-dominated fauna in the Rancholabrean suggests a shift toward more arid conditions during the Pleistocene.