Jacob Mikanowski at The Atlantic:
Unlike the other long-lived megafauna, Steller’s sea cows, one of the last of the Pleistocene survivors to die out, found their refuge in a remote scrape of the ocean instead of on land. The sea cows were relatives of the manatee and dugong. Unlike those two species, they were adapted to living in frigid Arctic waters. They were also much larger, growing to be as long as 30 feet from tail to snout, versus 10 for a manatee. Before the Ice Age, they seem to have been ubiquitous along the edge of the Pacific, living everywhere from Japan to the Baja Peninsula. By the 18th century, when they were first made known to Western science, the sea cows were confined to waters surrounding two tiny Arctic Islands in the Commander Chain, in between the Aleutians and the Kamchatka Peninsula.
The sea cows were first described by the German naturalist Georg Steller in the 18th century. Steller was part of an expedition organized led by the Danish explorer Vitus Bering. Financed by the Imperial Russian government, its mission was to chart the waters between Siberia and North America, and find a workable route between the two if possible.