Comments: The two geographically isolated subspecies (O. r. divergens in Pacific, O. r. rosmarus in Atlantic) exhibit distinct differences in mtDNA haplotypes and have slight differences in cranial morphology and tusk characteristics; walruses from different sampling locations exhibit mtDNA differences that may be useful in stock identification (Cronin et al. 1994).
Walruses occurring along the north coast of Asia, particularly in the Laptev Sea, are thought to have little contact with the other forms, and some Russian investigators recognize them as a third subspecies, O. r. laptevi (Reeves et al. 1992).
The Odobenidae has been regarded as a subfamily of the Otariidae by some authors; other authors contend that this would make the Otariidae paraphyletic (see Wozencraft, in Wilson and Reeder 1993). Odobenidae also has been regarded as a subfamily of Phocidae. Jones et al. (1992), Rice (1998), and Wozencraft (in Wilson and Reeder 1993, 2005) recognized the Odobenidae as a distinct family.