Trends in the paleodietary habits of fossil camels from the Tertiary and Quaternary of North America

Abstract

Dietary adaptations of both Tertiary and Quaternary representatives of North American Camelidae were examined through deep evolutionary time (via hypsodonty index), though ecological time (via mesowear analysis), and through the last few days of life (via microwear) by examining molar teeth. Fossil samples are from the Great Plains, Great Basin, Arizona, and Florida and span from the early late Eocene (late Chadronian–early Orellan) to the late Pleistocene (Rancholabrean). Results were compared to those obtained on modern camels and llamas and other ungulates of known dietary behavior. Camels apparently exploited open habitats early on in their evolution as evidenced by the extreme pitting of their enamel surfaces. Grasses were likely consumed early on in their history (e.g., Poebrotherium) but the vast majority of taxa were committed browsers. Results show that the hypsodonty pattern (deep time adaptation) and mesowear pattern (cumulative abrasion index) are very similar. Hypsodonty indices and mesowear scores decrease in the middle Miocene, a time when a few taxa also incorporate fruit and/or seeds in their browse. Crown height and dietary abrasion increase in the late Miocene and Pliocene, a time when some grazers and mixed feeders also appear, but then decrease in Pleistocene and Recent forms.