PALEOECOLOGY OF THE IRVINGTONIAN FAIRMEAD LANDFILL SITE, MADERA COUNTY, CALIFORNIA

Since the first fossil discoveries in 1993, Fairmead Landfill, located in the San Joaquin Valley of California, has produced thousands of vertebrate bone fragments, more than 3000 of which have been identified. Specimens collected between 1993 and 2008 comprise the Madera County Paleontology Collection (MCPC), which contains 2,964 identified elements. That collection, along with fossil pollen extracted from 39 samples of the surrounding sediments, enables us to imagine the San Joaquin Valley ecosystem between 0.78 and 0.55 Ma. Bones in the MCPC, derived largely from distal alluvial fan sediments, come primarily from mammals, the remainder being of turtle and a small assortment of birds, amphibians, fish, and other reptiles. Whereas identification of larger taxa is complete, rodents remain largely unidentified. The assemblage consists primarily of grazers, including Equus (61% by NISP), Mammuthus (7%), and Paramylodon (3%), moderate frequencies of mixed feeders Camelops (15%), Hemiauchenia (2%) and the probable halophyte browser Tetrameryx (2%). Odocoileus and Capromeryx, thought to be browsers, are rare. Rodents and Leporids identified to date consist primarily of Thomomys, Spermophilus, Microtus and Lepus, with Thomomys by far the most common. Carnivores, which account for less than 2% of the assemblage, include Canis dirus (0.7%), Smilodon (0.4%), and rare specimens of Lynx rufus, Canis latrans, and Taxidea. Sediment samples, processed by Global Geolab, generally produced only small quantities of pollen, although counts as high as 240 were encountered. Poaceae (grass) is consistently the dominant type, followed by Pinus. Many samples also contain Cupressaceae (probably Juniperus) and Chenopodiceae/Amaranthaceae. Pollen from deciduous trees and aquatic habitats is rare. The assemblage is indicative of a mesic grassland with halophytic shrubs growing on small, seasonally dry basins and scattered juniper occupying rocky or protected settings. Pine occupied forested uplands. Taken together, the paleontological and palynological records indicate a flora not unlike that of the historic Central Valley, but lacking the characteristic oak savannahs and occupied by herds of horse and camel preyed upon by dire wolves and sabertooth cats.