BEATTY, B. L.; Howard University, Washington, DC: Cornwallius sookensis (Desmostylia, Mammalia): New Material and its Implications for Suction Feeding

Cornwallius sookensis is one of the oldest known members of the extinct Order Desmostylia, a group traditionally interpreted as semiaquatic and hippo-like because of their resemblances to Hippopotamus and to their close tethytherian cousins, Moeritherium (a basal Proboscidean) and Pezosiren portelli (a basal Sirenian). It was previously known only as fossil teeth from Alaska, British Columbia, and Mexico. I describe additional material from the coast of Oregon that included two crania, two mandibulae, and several isolated molars and examine the identity, possible sexual dimorphism, and possible feeding mechanism in the taxon. A deeply concave hard palate and narrow oral opening is seen in this taxon as well as other desmostylian taxa. This vaulted palate has been identified as a structure associated with expanding the volume of the oral cavity and allowing for an enlarged tongue to be used as a piston for suction feeding in Odobenus (walrus) and other aquatic taxa. The wear pattern observed on the lingual aspect of the molars of C. sookensis indicates abrasion from sand or food items between the tongue and molars. These two characteristics along with taphonomic associations indicate that C. sookensis and possibly other desmostylians were suction-feeders in shallow water environments. Despite the evidence for aquatic feeding, no evidence is found that indicates that C. sookensis had negatively buoyant distal limb elements such as that found in Hippopotamus, suggesting that C. sookensis could float if swimming.