Desmostylus hesperus
Miocene
Temblor Formation
Fresno County, California, USA

Beautiful 42mm molar on 63mm matrix

Desmostylus is an extinct genus of marine mammals that lived during the Oligocene and Miocene epochs, approximately 23-5 million years ago. Desmostylus belongs to the order Desmostylia, a group of aquatic mammals that were once thought to be related to the sirenians (manatees and dugongs), but are now considered to have a more distant relationship with them.

Desmostylus was a large animal, with a stocky body and a short tail. Its limbs were short and robust, with hoof-like bones that may have been used for walking on land or foraging on the ocean floor. It likely lived in shallow waters along the coastlines of the North Pacific, feeding on seaweed and other aquatic vegetation.

Desmostylus is known from fossils found in Japan, California, and Oregon. Its name means “bonded pillar” in Greek, referring to the unique structure of its teeth, which were arranged in rows like columns and may have been used for grinding tough plant material. Desmostylus is an important part of the evolutionary history of marine mammals, and scientists continue to study its fossils to learn more about its ecology, behavior, and relationships to other groups of animals.