Inland California during the Pleistocene-Megafaunal stable isotope records reveal new paleoecological and paleoenvironmental insights

We measured oxygen and carbon isotope compositions from teeth from three fossil localities in California, The McKittrick Tar seeps (Rancholabrean), Fairmead Landfill, and Irvington (both Irvingtonian). These sites have produced a variety of megafauna fossils, and to date are relatively understudied. Previous ecological studies of Pleistocene California megafauna have focused on the coastal Rancho La Brea tar seeps (RLB), neglecting inland faunas. Both Fairmead Landfill and McKittrick are located in California's San Joaquin Valley, and provide the first isotopic data from the region. We sampled a wide range of taxa; Equus, Camelops, Mammuthus, Mammut, Hemiauchenia, Odocoileus, Tetrameryx, Capromeryx, Platygonus, Canis dirus, Canis latrans, Arctodus simus, Smilodon, Homotherium, Miracinonyx, Panthera onca and Panthera atrox. Stable carbon values from both middle Pleistocene localities are consistent with a C3 dominated environment. Mean annual precipitation (MAP) estimates for the middle Pleistocene localities are ~ 340 mm/year for Fairmead Landfill and ~ 900 mm/year for Irvington. While the inland MAP estimate is similar to modern levels, Irvington MAP estimates are significantly higher than the modern average. In contrast, the McKittrick tar seeps show clear evidence of C4 consumption among Equus, Bison and Camelops, suggesting a mixture C4 grasses and halophytes. Similarly, comparing between McKittrick and published data for RLB indicate a higher level of C4 resources inland. Serially sampled teeth from both inland localities reveal diet and resource partitioning between browsers and grazers.