Pleistocene paleoecology and feeding behavior of terrestrial vertebrates recorded in a pre-LGM asphaltic deposit at Rancho La Brea, California

Abstract

Sixteen taxa comprising extinct megafauna and extant species from a single asphalt deposit (Project 23, Deposit 1) at Rancho La Brea were isotopically analyzed (δ13C, δ15N, δ34S) and 14C dated to investigate paleoecology and feeding behavior of terrestrial vertebrates in southern California during the late Pleistocene. The large majority of the 14C dates cluster between ~35 and 36 kyr BP, but a range of ages indicate this seep was active from ~30 to >43 kyr BP. Many of the Smilodon fatalis and Canis dirus as well as the Canis latrans have similar δ13C (~–19‰ to −18‰) and δ15N (~11‰ to 12‰) results, indicating that these predators may have consumed similar prey species and possibly competed with each other through hunting and/or scavenging. The remains of contemporary potential prey species for these three predators include juvenile Bison antiquus and Camelops hesternus, and possibly adult Paramylodon harlani and Capromeryx minor. However, the δ15N results of a single C. dirus (8.9‰) and the Panthera atrox (8.3‰) were significantly lower than the other large predators. Potential prey for this dire wolf and lion include Nothrotheriops shastensis, Equus occidentalis and possibly Mammut americanum. Many of the herbivores appear to have utilized broadly similar C3 ecological environments. However, the adult E. occidentalis had isotopic results similar to the Sylvilagus sp. and Spermophilus beecheyi that have restricted home ranges, suggesting this horse was similarly local in its distribution or consumed a similar plant food selection. The isotopic values for extant taxa (Actinemys marmorata, Crotalus sp., Mustela frenata) suggest similar dietary patterns to their modern counterparts, indicating their ecological niches have remained relatively constant. The results presented here establish a foundation for future diachronic studies to better understand how the climate of the last ~50 kyr BP impacted biodiversity and ecological communities in southern California.