Carbon and nitrogen isotopic analysis of Pleistocene mammals from the Saltville Quarry (Virginia, USA): Implications for trophic relationships
The late Rancholabrean (N10,000 years ago) Saltville Quarry in Virginia, USA preserves a community of basal herbivores, including several families of giant mammals, representing a range of potential feeding strategies (browsers versus grazers) and digestive mechanisms (ruminants versus non-ruminants). In this study, carbon and nitrogen isotopic analysis of well-preserved bone collagen from a variety of body elements was used to determine the trophic relationships among these herbivores. A range of δ 15 N values was observed with ruminants and non-ruminants clustering into two distinct groups. Analysis of a young mammoth revealed a relatively high δ 15 N composition, which is consistent with a milk-dominated diet and supports the previously noted “juvenile effect” observed in the isotopic analyses of sub-adult mammals. In addition, the isotopic evidence supports the view that a giant ground sloth was primarily herbivorous, as opposed to competing hypotheses for an omnivorous or carnivorous nature. The measured 13 C abundances across the range of mammals, and of fossil organic matter, indicate a lack of C-4 grasses in the regional environment and a reliance on C-3 vegetation by all herbivores included in this study. These findings may record a regional geographic transition between C-3 and C-4 dominated grasslands. However, the overlapping isotopic signatures may also be considered as a potential indicator of extreme competition amongst the basal herbivores in this ecosystem, which has broader implications for the subsequent mass extinction of mega-herbivore clades at the end of the Pleistocene epoch. © 2007 Elsevier B.V. All rights reserved.