RECONSTRUCTING THE LIFESTYLE AND HABITAT OF THE DESMOSTYLIAN BEHEMOTOPS

Oligocene and Miocene sites along the Strait of Juan de Fuca have produced important, and often enigmatic, marine vertebrate fossils including desmostylians, plotopterids, and pinnipeds. Much of the research on these taxa has focused on morphology, taxonomy, and phylogenetics, while less is known about their paleoecology and the environments they lived in. For example, the desmostylian Behemotops, known from one locality in Japan, one on Vancouver Island, and two on the Olympic Peninsula, has been interpreted as leading a more pelagic lifestyle than its relatives based on bone density. Paleoenvironmental reconstructions could shed light on this hypothesis, as a more fully marine taxon would be expected to be found more commonly in deep water environments than other desmostylians. We conducted both museum- and field-based analyses on the paleoenvironment of Behemotops localities along the Strait of Juan de Fuca to determine whether Behemetops is consistently recovered from deep marine environments. Our work focused on the two regional formations from which Behemotops has been recovered: the Clallam (Washington) and Sooke (British Columbia) Formations. We gathered abundance data for marine invertebrates from these localities from museum collections. Using these data, we performed cluster analyses to identify the range of environments preserved in each formation. We also visited each of the regional Behemotops localities, along with other nearby marine mammal sites. At each locality, we observed lithology and fossilized organisms to determine where the sediments were deposited (deep ocean or shallow water) as well as energy levels at the site. We found that the Behemotops was exclusively found in mudstone indicating a deeper, lower energy environment. This observation is corroborated by the presence of invertebrates such as Dentalium characteristic of deep marine ecosystems. Our findings support the morphology-based interpretation that Behemetops lived much like a pinniped and lay the foundation for similar analyses of marine mammal paleobiology in the region.