PHYLOGENY OF NEW EARLIEST PALEOCENE (PUERCAN) PERIPTYCHID ‘CONDYLARTHS’ FROM THE GREAT DIVIDE BASIN, WY

An earliest Paleocene (Puercan) fauna discovered by the late James Honey and Malcolm McKenna in the lower China Butte Member of the Fort Union Formation in Wyoming’s Great Divide Basin (GDB) contains a diverse mammalian faunal assemblage, including a number of ‘condylarth’ taxa. Preliminary studies by others have suggested that this faunal assemblage may be correlative with the early Puercan Littleton fauna in the Denver Basin, due to multiple shared taxa. The fauna from UCM locality 2011035 includes at least three new periptychid ‘condylarth’ genera. One new genus (referred here to Gen. et sp. nov. A) is based on a left dentary containing p3 – m3, is 10-12% larger than Conacodon delphae (the largest documented species of Conacodon) and appears similar in morphology to Auraria urbana but differs in having more inflated cusps. A second new genus (Gen. et sp. nov. B) is based on left and right dentaries containing Lp3 – m3 and Rp4 – m3, respectively. This new taxon appears close in molar morphology to species of Conacodon, differing primarily in its larger size and morphology of the p4. Finally, the third new genus of periptychid from the GDB (Gen. et sp. nov. C) is based on two right dentaries containing p4 – m3 and p3 – m3, as well as a left dentary containing p4 – m2. This new taxon appears close in morphology to Oxyacodon archibaldi, sharing a distinct paraconulid but differing in the placement of the paraconid. To examine the relationships between these new taxa and other Puercan periptychids from the Western Interior of North America, a phylogenetic analysis was performed using 20 ‘condylarth’ taxa and 56 dental characters. Characters were aggregated from previous phylogenetic analyses of ‘condylarth’ taxa and scored based on comparative study with specimens from several museum collections as well as descriptions of teeth from the literature. The preliminary phylogenetic analysis suggests that Gen. et sp. nov. A appears closely related to Auraria urbana and Ampliconus browni, while Gen. et sp. nov. B appears to be a sister group to the Conacodontines, and Gen. et sp. nov. C forms a clade with Oxyacodon archibaldi. If prior estimates of an early Puercan age for UCM locality 2011035 are correct, then the occurrence of three new periptychid taxa suggest that mammalian diversity is higher than previously thought for the earliest Paleocene.