Steller's sea cow

Steller's sea cow (Hydrodamalis gigas) is a sirenian discovered by Europeans in 1741. At that time, it was found only around the Commander Islands in the Bering Sea between Alaska and Russia; its range was more extensive during the Pleistocene epoch, and it is possible that the animal and humans previously interacted. Some 18th-century adults would have reached weights of 8–10 t (8.8–11.0 short tons) and lengths up to 9 m (30 ft).

It was a part of the order Sirenia and a member of the family Dugongidae, of which its closest living relative, the 3 m (9.8 ft) long dugong (Dugong dugon), is the sole surviving member. It had a thicker layer of blubber than other members of the order, an adaptation to the cold waters of its environment. Its tail was forked, like that of cetaceans. Lacking true teeth, it had an array of white bristles on its upper lip and two keratinous plates within its mouth for chewing. It fed mainly on kelp, and communicated with sighs and snorting sounds. Evidence suggests it was a monogamous and social animal living in small family groups and raising its young, similar to extant sirenians.

Steller's sea cow was named after Georg Wilhelm Steller, a naturalist who discovered the species in 1741 on Vitus Bering's Great Northern Expedition when the crew became shipwrecked on Bering Island. Much of what is known about its behavior comes from Steller's observations on the island, documented in his posthumous publication On the Beasts of the Sea. Within 27 years of discovery by Europeans, the slow-moving and easily caught mammal was hunted into extinction for its meat, fat, and hide.