TEMPORAL PATTERNS IN THE DIETARY ECOLOGY OF LATE PLEISTOCENE MAMMALIAN CARNIVORES FROM RANCHO LA BREA

When humans migrated into North America during the late Pleistocene they encountered ecosystems that hosted very diverse mammalian faunas. The trophic interactions among top mammalian consumers within these food webs may have influenced the availability of herbivores (both on the hoof and through scavenging) for humans. In this study I used stable isotope data to investigate the dietary ecology of mammalian carnivores from 30, 15 and 11ka. Specifically, I used the d¹³C and d ¹⁵N values of bone collagen from two extinct carnivore species (Smilodon fatalis and Canis dirus) from the La Brea tarpits in southern California. Extensive morphometric and faunal analyses of the carnivore assemblage at La Brea suggest a shift in their feeding habits near the end of the Pleistocene, potentially in response to dietary stress. Stable isotope data from bones and teeth can complement these previous studies by further characterizing the dietary interactions of the La Brea carnivore guild.

Isotopic results demonstrate that although both carnivore species were feeding within a C₃ plant ecosystem throughout the late Pleistocene, their dietary ecologies differed. S. fatalis had a constant average d ¹³C value through time, but there was a significant decrease in the values of C. dirus at 11ka. The higher d ¹³C values of C. dirus at 30 and 15 ka cannot yet be explained by currently analyzed prey species. S. fatalis had a constant average d ¹⁵N value with low variability, indicating a limited prey base. There was a significant increase in S. fatalis d ¹⁵N variability through time possibly reflecting a more diverse prey base at 11 ka. C. dirus had a similar average d ¹⁵N value, but with higher variability than that of S. fatalis. This suggests that C. dirus was a generalist and scavenger with a wide prey base. In general, there appears to be a shift in the diet of both species from 15 to 11ka, correlating to both established environmental change and the possible arrival of humans in the area.