Rancho La Brea stable isotope biogeochemistry and its implications for the palaeoecology of late Pleistocene, coastal southern California

We sampled 143 individuals from Rancho La Brea (RLB) large faunal collections for bone collagen stable carbon (δ13C) and nitrogen (δ15N) isotope ratios. These collections were recovered from asphalt seeps in the Los Angeles Basin, California, USA, and date from ∼40 to 12 ka. Our findings indicate that despite a slight reduction in collagen nitrogen content, RLB skeletal remains are relatively well preserved and most yield proteins diagnostic of diet. Herbivore δ13C and δ15N values covary with rumination and are consistent with changes in late Pleistocene vegetation reconstructed from pollen profiles. We find no evidence for reliance on C4 grasses at RLB, despite low atmospheric CO2 concentrations. Carnivore δ15N values indicate Canis dirus, Smilodon fatalis and Panthera leo atrox competed for similar prey sets and were equally reliant on ruminant and nonruminant prey types. The δ15N values of Mammut americanum indicate partial reliance on vegetation with lower δ15N values (such as nitrogen-fixing taxa), distinguishing them from the remainder of the study population. A comparison of RLB and European faunal δ15N values from the late Pleistocene suggests that coastal southern California experienced greater aridity.