Enaliarctos

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Enaliarctos
Fossil range: Early Miocene

Enaliarctos emlongi and Macrodelphinus (background).

Fossil

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Infraorder:	Pinnipeda
Family:	Enaliarctidae
Genus:	Enaliarctos Mitchell & Thedford, 1973

Species

E. mealsi (type)
E. barnesi
E. emlongi
E. mitchelli
E. tedfordi'

Enaliarctos is an extinct genus of pinniped.

Five species in the genus Enaliarctos represent the oldest known pinniped fossils, and have been recovered from the late Oligocene (ca. 27 million years ago) and early Miocene (ca. 17 Ma) of California and Oregon. It had a short tail and developed limbs with webbed feet. Unlike modern sea lions, it had a set of slicing carnassials; the presence of slicing (rather than purely piercing teeth in modern fish eating pinnipeds) suggests that Enaliarctos needed to return to shore with prey items in order to masticate and ingest them. Still, Enaliarctos had some sea lion-like characteristics such as large eyes, sensitive whiskers and a specialized inner ear for hearing sound under water.

Enaliarctos has been heralded as the ancestor of all known pinnipeds, including the families Otariidae (fur seals and sea lions), Desmatophocidae (extinct seal convergent pinnipeds), Phocidae (true seals), and Odobenidae (walruses). Investigations of the biomechanics of Enaliarctos indicate that it used both its forelimbs and hindlimbs during swimming. Modern fur seals and sea lions only use their forelimbs, while true seals primarily use their hindlimbs for aquatic propulsion; lastly, the extant walrus uses both fore- and hindlimbs for swimming. It has been postulated that the condition in Enaliarctos is ancestral for all pinnipeds, and that forelimb swimming was lost in true seals, and hindlimb swimming was lost in fur seals and sea lions. This is significant because there has been considerable debate as to whether pinnipeds share common ancestry. Interpretation of Enaliarctos indicates that all pinnipeds share a common ancestor (which, if it was not Enaliarctos, was something very similar).

[edit] References

Berta, A., C.E. Ray and A.R. Wyss. 1989. Skeleton of the oldest known pinniped, Enaliarctos mealsi. Science 244:60-62.
Berta, A. 1991. New Enaliarctos* (Pinnipedimorpha) from the Miocene of Oregon and the role of "Enaliarctids" in Pinniped Phylogeny. Smithsonian Contributions to Paleobiology 69.
Dixon, D., Moody, R., Jenkins, I. and Zhuravlev, A.Y., Cassell's Atlas of Evolution. Oxford 2001