Sea of Japan Exhibit: Desmostylus
This skeleton is a reconstruction of a peculiar mammal known as the Desmostylus, which lived in coastal areas of the Pacific Ocean between 28 and 11 million years ago. Although individual specimens varied in size, on average Desmostylus was 1.8 meters long and weighed around 200 kilograms. It is believed to have resembled a small hippopotamus.
Desmostylus’ name comes from two Greek words meaning “bond” (desmos) and “pillar” (stulos). The name is a reference to its unusual molars, which look like seven circular columns bound together. One such molar, the first Desmostylus fossil found in Japan, was uncovered here in Shimane Prefecture, on the shore of Lake Shinji.
During the early Miocene epoch, about 20 million years ago, the Sea of Japan was a broad, shallow expanse with a relatively mild climate. These conditions were perfect for Desmostylus, which likely spent its days in the water, foraging for aquatic plants. Research completed in 2013 suggests that unlike the semi-aquatic hippo, Desmostylus was fully aquatic. This theory is based partly on its bone structure, which was less dense than that of land-dwellers and would have made it a good swimmer.
It is difficult to form a detailed understanding about Desmostylus, because there are no living descendants of the Desmostylia order. However, fossils indicate there were at least three species: D. hesperus, D. coalingensis, and D. japonicus.