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

Abstract

We sampled 143 individuals from Rancho La Brea (RLB) large faunal collections for bone collagen stable carbon ( δ 13C) and nitrogen ( δ 15N) 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 δ 13C and δ 15N values covary with rumination and are consistent with changes in late Pleistocene vegetation reconstructed from pollen profiles. We find no evidence for reliance on C 4 grasses at RLB, despite low atmospheric CO 2 concentrations. Carnivore δ 15N 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 δ 15N values of Mammut americanum indicate partial reliance on vegetation with lower δ 15N values (such as nitrogen-fixing taxa), distinguishing them from the remainder of the study population. A comparison of RLB and European faunal δ 15N values from the late Pleistocene suggests that coastal southern California experienced greater aridity.