Was grass more prevalent in the pronghorn past? An assessment of the dietary adaptations of Miocene to Recent Antilocapridae (Mammalia: Artiodactyla)

Molar teeth of both Tertiary and Quaternary representatives of the family Antilocapridae were examined using mesowear and light stereomicroscopy microwear. Taxa from the Central and Southern Great Plains and the Northern and Southern Great Basin were included in the analyses and results compared to those obtained on the modern pronghorn (Antilocapra americana). Species included spanned from the early Miocene (late Hemingfordian) to the late Pleistocene (Rancholabrean). Results are concordant with well-known trends toward increasing aridity and shifts in vegetational structure in the late Miocene–early Pliocene of North America. Both mesowear and microwear results indicate a shift toward more abrasive diets beginning in the Hemphillian (late Miocene–Pliocene) and then a return to a less abrasive dietary regime for the duration of the Pleistocene and into the Recent. The more derived antilocaprines (more hypsodont, relatively longer limbs) apparently depended more on grass than the less advanced merycodontines, but even the earliest of the latter seem to have relied more on grass as a dietary staple than the modern pronghorn. Seasonal grit encroachment on food items encountered by fossil antilocaprids coupled with a heavier reliance on grasses may provide a possible explanation for the extreme hypsodonty present in the modern pronghorn despite its mainly browsing dietary behavior.