Meeting Abstract

P1.83  Sunday, Jan. 4  Stable Isotope Analysis of Pinniped fossils from the San Diego Formation (Late Pliocene, California) CHURCHILL, Morgan M.*; CLEMENTZ, Mark; University of Wyoming; University of Wyoming mchurch3@uwyo.edu

Pinnipeds (seals and allies) represent an intermediate morphological and ecological condition between fully aquatic marine and terrestrial mammals and as such are an ideal group for study of the land-sea transition in tetrapods. Morphology has been the primary focus of most studies of fossil pinnipeds, but supplemental ecological information can be gained through stable isotope analysis of fossil material. Tooth enamel is the preferred material for stable isotope analysis because it is less prone to diagenetic alteration. For studies of fossil pinnipeds, however, this presents a problem as most taxa exhibit a reduction in enamel and in the number and size of teeth. Here we assess the use of other biogenic materials (i.e., bone, dentin) as potential archives of ecological information for pinnipeds. Bone and dentin were sampled for carbon and oxygen stable isotope analysis from the Late Pliocene San Diego Formation of southern California. Taxa sampled include three species of fossil pinniped as well as coeval species of whales, sirenians, fish and terrestrial mammals. Three types of criteria were defined to assess the extent of diagenetic alteration in bone and dentin: 1) comparison of phosphate oxygen values with carbonate oxygen values; 2) similarity and degree of overlap in carbon values among ecologically distinct taxa; and 3) how well the recorded isotope values fit predicted values for Pliocene marine consumers. Once validated, these tools will then be applied to study of earlier species representing the initial radiation of pinnipeds into aquatic ecosystems.