19 La Brea Tar Pits: Old Bones and New Insights

Wednesday, 13 May 2020
8:00 AM - 12:00 PM
San Rafael

NEW INSIGHTS FROM THE STABLE ISOTOPES OF BONES AND TEETH FROM RANCHO LA BREA CARNIVORANS

Paper number: 19-8
Program: Theme Sessions
Time: 10:15 AM – 10:35 AM

Authors

Abstract

Isotopic studies of Rancho La Brea predators have yielded disparate dietary interpretations when analyzing δ13C in bone collagen vs. enamel carbonate in hypercarnivores—indicating competition for similar prey via bone collagen and disparate prey via enamel carbonate. Reconciling these dietary interpretations is critical to evaluating the ecology of Late Pleistocene mammals at Rancho La Brea, one of the most fossiliferous localities in the world. Exploration of the stable carbon isotope (δ13C) relationship between collagen and carbonate has helped clarify the debate over ancient carnivoran dietary habits. Stable carbon isotope spacing between collagen and carbonate has been characterized as a proxy for inferring the trophic level of mammals for decades. Carbonate-collagen offsets (c-c offsets) are assumed as largely stable among taxa feeding at similar trophic levels, with higher offset values indicative of more omnivorous/herbivorous diets in secondary consumers. To clarify the stable isotope ecology of carnivorans, past and present, we isotopically analyzed bone collagen and enamel carbonate of extinct and extant felids and canids, including dire wolves (Canis dirus), sabertooth cats (Smilodon fatalis), coyotes (Canis latrans), and pumas (Puma concolor). Our results reveal that c-c offsets can be predicted via enamel carbonate values in secondary consumers, with lower c-c offsets occuring coincident with lower carbonate values, not trophic levels. These results indicate that the foraging habitat of prey affects c-c offsets in carnivores, similar to the relationship for c-c offsets observed in herbivores. Further, variable c-c offset values in secondary consumers appear to reconcile the disparate dietary interpretations of S. fatalis and C. dirus. Trophic level, physiological differences between felids and canids, and ontogenetic dietary differences do not appear to be primary drivers of c-c offsets —challenging long-held assumptions pertaining to carbonate-collagen spacing and providing clarity to the dietary behavior of extinct predators.

Geological Society of America Abstracts with Programs. Vol. 52, No. 4

doi: 10.1130/abs/2020CD-347138

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