 "Thalassocnus" went extinct at the end of the Pliocene due to a cooling trend that followed the closing of the Central American Seaway which killed off much of the seagrass of the Pacific South American coast.As seagrass specialists, the later species of "Thalassocnus" had evolved negative buoyancy to allow them to feed at the sea floor, similar to modern dugongs.This feeding style probably involved bottom-walking, like hippopotamuses and the extinct desmostylians, and digging.