A protocol for differentiating late Quaternary leporids in southern California with remarks on Project 23 lagomorphs at Rancho La Brea, Los Angeles, California, USA

Abstract

Leporid remains are common in Quaternary fossil assemblages and are useful paleoenvironmental indicators. Identifying leporid fossils to species is challenging, though previous work has shown that identifications are more feasible if fossils can be narrowed down to a subset of potential species occurring across limited spatial scales. We sampled 120 adult and nine juvenile dentaries of six extant western North American species (Lepus americanus, L. californicus, L. townsendii, Sylvilagus audubonii, S. bachmani, and S. nuttallii) to establish useful characters for genus and species-level identification of late Quaternary leporid fossils in California. Most individuals can be differentiated from individuals of other species using a combination of lower third premolar enamel folding patterns and dental measurements. However, it is difficult to discriminate dental elements among L. californicus and L. townsendii and elements of S. nuttallii from S. audubonii, S. bachmani, and L. americanus. Here we present criteria for differentiating western leporid dental remains, apply the criteria to identify specimens recovered from several late Quaternary fossil deposits at Rancho La Brea (RLB), California, collectively known as Project 23, and reconstruct changes in relative fossil leporid abundances there. Using our criteria, we identified two extant species, S. audubonii and S. bachmani, among the Project 23 fossils. In addition to relative abundance changes across several RLB deposits, S. audubonii and S. bachmani generally become larger through time, possibly in response to local environmental changes. Establishing region-specific identification criteria as done here may prove useful for discerning morphologically similar species at prehistoric sites elsewhere.