Steller's Sea Cows were the only Arctic members of the order Sirenia, which includes modern Manatees and Dugongs. They were also the largest; Steller recorded specimens as long as 28 feet. This dwarfs modern Sirenians which rarely grow larger than 12 feet. Steller's Sea Cows were also herbivores, which differs from most other marine mammals. They fed off of kelp and various algae. They lived in herds and were described by Steller as being monogamous.
Steller's Sea Cows were confined to arctic waters, though ancestral species within the same genus had a wider range that spread down as far as Southern California. They, and all other Sirenians, are most closely related to Hyraxes, small rodent-looking creatures. They are also distantly related to Elephants and other members of the Superorder Afrotheria.