DOES OREODONT MORPHOLOGY AND THEIR EXTINCTION CORRELATE WITH GRASSLAND EXPANSION IN NORTH AMERICA’S CENTRAL-WESTERN GREAT PLAINS?

Oreodonts are one of the most abundant, widespread, and diverse mammal groups in early Neogene North America. Yet, they went extinct in the late Miocene while other less abundant groups such as camels and peccaries survived. As grasslands expanded during the Miocene, open savannas replaced closed forests. This change increased selection for grazing morphologies reflecting a change of diet. As distances between feeding patches increased, efficiency of locomotive morphology (cursoriality) should become more widespread among species of surviving clades. To assess the response of oreodonts to environmental change and their likelihood for extinction, a series of 30 skull attributes and 34 postcranial attributes were measured. Of the 201 individuals, 98 include associated jaw and cranial elements, and 61 include associated skull and limb elements. All skeletal elements have been evaluated for deformation to ensure proportional accuracy in each measurement.

Preliminary results using principal component analysis indicate a trend through time toward grazing morphologies in the anterior skull and limbs. Although, no correlation between body size and geologic age is observed, a temporal trend from specialist to generalist traits is correlated with decreasing diversity. Primary trends occur early, in the Oligocene, followed by diffusion into a wider, generalist morphospace in the Miocene. Despite this early shift toward grazing morphologies, oreodonts went extinct at the end of the Miocene.

Future research will investigate the amount and timing of change for the same morphological attributes in camels and peccaries. Then quantitative comparisons with oreodonts can be made to determine whether differences in morphological changes among oreodonts, camels, and peccaries can explain why oreodonts went extinct. Testing for correlation between extinction and changes in environment and morphology in deep time on empirical datasets like oreodonts is fundamental to our understanding of diversity and evolution and essential to developing models to interpret extinction risk in modern ecosystems.