Evolution and systematics

There has been a long standing controversy as to whether the Pinnipedia is diphyletic (arising from two lines) or mono-phyletic (arising from a single line). The majority of morphological and DNA evidence now supports monophyly, with an arctoid ancestor (probably ursid, but could be mustelid or procyonid). However, still uncertain is where odobenids fit within this lineage. Most morphological evidence supports a closer relationship between odobenids and phocids although at least one morphological study places the odobenids and otariids closer together. Molecular genetic studies generally support a closer relationship between the odobenids and otari-ids, but there are some studies that suggest the relationship with phocids. In short, additional study is required to clarify the evolutionary position of the Odobenidae within the Pinnipedia. Currently three subspecies of walrus are recognized, the Pacific, Atlantic, and Laptev walruses, although there is disagreement on whether the Laptev group is distinct enough to be considered a subspecies.

The taxonomy for this species is Odobenus rosmarus (Linnaeus, 1758), "intra zonam arcticam Europae, Asiae, Americae."

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