Drawing of Steller's sea cow, by Georg Steller.

The sea cow grew up to 7.9 meters (25.9 ft) long and weighed up to three tons, much larger than the manatee or dugong. Steller's work contains two contradictory weights: 4 and 24.3 tons. The true value may lie between these figures. 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". It was completely tame, according to Steller. They fed on a variety of kelp. Wherever sea cows had been feeding, heaps of stalks and roots of kelp were washed ashore. The sea cow was also a poor swimmer and is not believed to have been able to dive.