PREDATOR-PREY RATIOS IN THE OLIGOCENE WHITE RIVER BADLANDS

The late Oligocene deposits of the White River Badlands represent one of the richest fossil assemblages in the world. Specimens identified from one locality in northwestern Nebraska, Shalimar Ranch, belong to at least 18 separate genera, showing that this site is representative of the fauna as a whole. Of the two White River formations, the Chadron and the Brule, only collections from the latter, younger formation were examined in this study. Predator-prey biomass ratios calculated from specimens collected at this site over the last twenty years fall directly into the percentile predicted by Bakker (1975) for endothermic predation. The prey species, both Perrisodactyls like the early horse Mesohippus and Artiodactyls such as the sheep-like, herding Merycoidodon, accounted for nearly ninety-nine percent of the fauna's biomass (excluding ectotherms such as the Badlands' omnipresent turtle species). The predators from this site include extinct dog and cat genera. Although the rare creodont Hyaenodon has been reported from the Brule in other studies (O'Harra 1920, Bakker 1975), the Shalimar site has provided no verifiable specimens of this genus. Still, the ratio percent of predator-prey biomass of 1.2 percent falls just within the range predicted by Bakker for endothermic fossil assemblages. If anything the number is too low, suggesting that instead of herbivory with opportunistic scavenging, Archaeotherium, the giant pig included as an artiodactyl prey species did indeed participate in active mammalian predation.