New Middle Eocene omomyines (primates, haplorhini) from the Friars Formation of San Diego County, Southern California

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Atwater, Amy Lynn

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The Friars, Mission Valley, Santiago, and Sespe formations in Southern California are composed of fluvial sediments and represent the Uintan North American Land Mammal Age. The omomyoid primates currently recognized from the Uintan of San Diego County include Dyseolemur, Chumashius, Hemiacodon, Washakius, Macrotarsius, Stockia, Yaquius, and Ourayia. Here we describe three new genera of Middle Eocene primates from the Friars Formation of San Diego County. Thirty-two teeth represent Ekwiiyemakius. Ekwiiyemakius is the smallest of the new taxa and has an estimated body mass of 119 g. This new genus is distinguished by a discontinuous lingual cingulum and a waisted distal margin on the upper molars. Sixty-four specimens represent Cabrillotarsius. At 289 g estimated body mass, Cabrillotarsius is intermediate in size. Cabrillotarsius has a distinctive upper fourth premolar with a mesio-buccally oriented protocone and upper molars with a strong, lingually continuous cingulum. A sample of thirty-nine teeth and mandibular fragments represent a third new genus, Brontomomys. With an estimated body mass of 757 g, this large omomyine is similar in size to Macrotarsius jepseni. However, Brontomomys is distinct from other large omomyines in having a small p4 paraconid and large m2-m3 paraconids that are twinned with the metaconid. The results of phylogenetic analyses vary according to (1) the choice of character-taxon matrix and (2) the use of parsimony versus Bayesian tree building methods. Nevertheless, all preliminary phylogenetic analyses are congruent in recovering a close relationship between the three new San Diego taxa and the omomyines Ourayia, Macrotarsius, Utahia, and Omomys. Prior research has documented a shift in omomyoid diversity in North America from the anantomophine-rich Bridgerian to the omomyinerich Uintan. Our description of three new Uintan omomyine taxa further emphasizes these opposite trends in anaptomorphine and omomyine species richness during the Middle Eocene. All of the new taxa are currently only known from the Friars Formation in San Diego County, California. Four of the previously known genera from San Diego County (Dyseolemur, Chumashius, Yaquius, and Stockia) are endemic to Southern California, further highlighting the provincial character of primate faunas in Utah, Southern California, and West Texas during the Uintan



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