NICHE PARTITIONING IN AN OLIGOCENE CARNIVORE GUILD

The Turtle Cove Member (~32-25.9 Ma) of the John Day Formation in central and eastern Oregon consists of 14 lithostratigraphic subunits (A-K2). The faunal assemblage of subunit F (28.8-28.7 Ma) is assigned to the Early Early Arikareean (Ar1 subage), and the unexpectedly high diversity of canid taxa present makes this assemblage one of particular interest. Ten species of canid are represented in this subunit, while the highest diversity of canids coexisting in a modern ecosystem is five, with three being a more typical number of sympatric canids. Through the Geoscientists-in-the-Parks program, we aimed to determine how niches were partitioned among the subunit F canids. We took measurements of carnassial blade length and relative premolar size, while an estimate of body mass was made from the length of the lower carnassial for each species. These data were then plotted in 3D morphospace. These three characteristics were found to be accurate indicators of diet in modern carnivores, grouping animals according to the amount of bone and non-vertebrate material in their diets. In addition to ten canid species, one nimravid, one vivveravid, and two amphicyonids were present in subunit F and were also included in the analysis so as to include the entire carnivore community. These results were then compared to niche partitioning in three modern ecosystems: Yellowstone National Park, the Serengeti of Africa, and peninsular Malaysia. It was found that the mosphospace occupied by carnivores in the Turtle Cove Member is overall very similar to modern ecosystems, though a greater number of families now occupy the small carnivore and insectivore niches that belonged almost exclusively to canids in the Turtle Cove ecosystem. Thus, the niches available to carnivores have changed little in the past 30 million years, though these niches are now occupied by a higher diversity of families.