Desmostylus fossil bones and teeth are among the rarest and most scientifically enigmatic prehistoric mammal specimens available, representing one of the only truly extinct orders of mammals with no living relatives whatsoever.
Quick Facts
| Common Name: Desmostylus | Scientific Name: Desmostylus hesperus | Meaning: Chain pillar |
| Period: Miocene (33-10 million years ago) | Diet: Herbivore | Size: Large |
| Length: Up to 1.8 meters (6 feet) | Weight: 200-300 lbs | Named by: Marsh, 1888 |
Overview
Desmostylus was a large semi-aquatic herbivorous mammal that lived along the coastlines of the North Pacific during the Miocene epoch. It belonged to the Desmostylia, a completely extinct order of mammals with no living relatives and no close connections to any living mammal group — making it one of the most evolutionarily isolated animals in the fossil record. Built somewhat like a hippopotamus it waded in shallow coastal waters browsing on aquatic plants. Its strange columnar teeth, shaped like bundles of parallel cylinders fused together, are unlike those of any other mammal and immediately identifiable. Desmostylus fossils are found along the Pacific coast from Japan to California and Alaska.
What to Look For
Desmostylus teeth are the most distinctive and commonly available specimens and are immediately recognizable — look for the characteristic parallel cylindrical cusps fused together in a cluster, completely unlike the teeth of any other mammal. The enamel is thick and resistant to wear. Bone from Pacific coast sites varies from dark brown to grey. Complete teeth are significantly more valuable than fragments. Given the rarity of this animal any claimed specimen should come with thorough provenance documentation.
Fun Facts
Desmostylia is one of the only truly extinct orders of mammals — the entire group vanished without leaving any living descendants or close relatives. Its teeth are unlike those of any other mammal, consisting of parallel cylinders fused together in a distinctive bundle shape. Recent research suggests it may have walked more like a bear than a hippo with its limbs positioned more underneath its body. It is known from both sides of the North Pacific making it one of the few fossil mammals with a trans-Pacific distribution. Its lifestyle and behavior remain debated with some researchers suggesting it fed like a walrus using its tusks to dig up sea floor vegetation.
Museum Research Articles
Learn more about the Desmostylus
- Britannica: Desmostylian
- Smithsonian Institution: Collection