New <I>Enaliarctos</I>* (Pinnipedimorpha) from the Oligocene and Miocene of Oregon and the Role of "Enaliarctids" in Pinniped Phylogeny

Abstract

Three new species of the pinnipedimorph <I>Enaliarctos*</I> are described from the marine late Oligocene and early Miocene (Arikareean and Hemingfordian or early Barstovian correlatives) of coastal Oregon. <I>Enaliarctos tedfordi</I>, new species, is based on a partial cranium from the late Oligocene Yaquina Formation. A related new species, <I>Enaliarctos emlongi</I>, is founded on a nearly complete cranium, jaws, and associated skeletal elements from the late Oligocene to early Miocene Nye Mudstone. A third new species, <I>Enaliarctos barnesi</I>, is based on a partial cranium and jaws from late Oligocene or early Miocene rocks near the contact between the Yaquina Formation and the Nye Mudstone. Another skull, from the Nye Mudstone, is referred to a previously described species, <I>Enaliarctos mitchelli</I> Barnes, 1979. Three of these species, <I>E. mitchelli, E. emlongi</I>, and <I>E. tedfordi</I> form a monophyletic clade, united by reduced cheek teeth cingula and short metacone of the upper carnassial. The major trend observed in <I>Enaliarctos</I> over 10 million years of history is an intermediate stage in the transformation to homodonty evidenced by premolarization of the upper carnassial and molars and reduction and simplification of cusps on the lower carnassial.<br/>Cladistic analysis of 52 cranial and dental characters suggests the following phylogenetic hypotheses: (1) the subfamily "Enaliarctinae" (&amp;equals; "Enaliarctidae") is paraphyletic, (2) monophyly of the genus <I>Enaliarctos*</I> is questioned although the status of this taxon as sister taxon to other pinnipeds is affirmed, (3) other "enaliarctid" pinnipeds, <I>Pteronarctos</I> and <I>Pinnarctidion</I>, are assigned to less inclusive pinniped clades (<I>Pteronarctos</I> + all other pinnipeds and <I>Pinnarctidion</I> + <I>Desmatophoca, Allodesmus</I>, and the Phocidae).