Steller's Sea Cow (Hydrodamalis gigas) is an extinct large sirenian mammal formerly found near the Asiatic coast of the Bering Sea. It was discovered in the Bering Strait in 1741 by the naturalist Georg Steller, who was traveling with the explorer Vitus Bering. A small population lived in the arctic waters around Bering Island and nearby Copper Island.

The sea cow grew up to 35 feet (10.7 meters) long and weighed up to three-and-a-half tons, much larger than the manatee or dugong. It looked somewhat like a large seal, but had two stout forelimbs and a whale-like tail. According to Steller, "The animal never comes out on shore, but always lives in the water. Its skin is black and thick, like the bark of an old oak..., its head in proportion to the body is small..., it has no teeth, but only two flat white bones—one above, the other below." They fed on a variety of kelp. Wherever sea cows had been feeding, heaps of stalks and roots of kelp were washed ashore.

The population of sea cows was small in number and limited in range when Steller first described them. They were wiped out quickly by the sailors, seal hunters, and fur traders that followed Bering's route past the islands to Alaska, who hunted them both for food and for their skins, which were used to make boats. By 1768, less than 30 years after it had been discovered, Steller's Sea Cow was extinct.

There are still sporadic reports of sea cow-like animals from the Bering area, however, so it has been suggested that small populations of the animal may have survived to the present day. This remains so far unproven.

See also:

• Extinction
• List of extinct animals
• List of extinct animals (U.S.)