The isotopic ecology of late Pleistocene mammals in North America

Mammoths and mastodons are common in Pleistocene deposits, yet these proboscideans and many other animals disappeared suddenly ≈10,000 years ago. In this study, we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late Pleistocene extinction. We analyzed specimens from six sites in Florida, ranging from full glacial (>21,000 BP) to late glacial (14,750 to 10,000 BP) age. The oxygen isotope composition of mammalian apatite covaries with meteoric water composition, which in turn varies with climate. Consequently, oxygen isotope analysis can be used to assess the potential for time-averaging or mixing of specimens from different geographic regions within fossil assemblages. The carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests. Carbon isotope analysis reveals that mastodons ate chiefly C3 plants, presumably trees, shrubs and herbs, whereas mammoths consumed chiefly C4 grass. Several nutritional hypotheses for late Pleistocene extinction entail the assumption that extinct taxa had specialized diets. The resource partitioning and focused feeding preferences of Florida's proboscideans corroborate this assumption, but they do not, in themselves, prove that nutritional stress was the cause of the late Pleistocene extinction.