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 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 Formation, due to multiple shared taxa. The fauna from UCM locality 2011035 includes a new periptychid ‘condylarth’ genus as well as a new species of Conacodon. The new genus, which 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 Alticonus gazini, but differs in having more inflated cusps, shorter molar talonids, and shallower basins. The new species of Conacodon is based on left and right dentaries that include the Lp3-m3 and Rp4-m3. This new species appears close in molar morphology to species of Conacodon and Hemithlaeus kowalevskianus (which occur at middle Puercan-aged localities elsewhere), differing primarily in its larger size and morphology of the p4. To examine the relationships between these two new taxa and other Puercan periptychids from the Western Interior of North America, a phylogenetic analysis was performed using 18 ‘condylarth’ taxa and 53 dental characters. Characters were aggregated from previous phylogenetic analyses of ‘condylarth’ taxa, and they were scored based on comparative study with specimens and casts from several museum collections as well as descriptions of teeth from the literature. The preliminary phylogenetic analysis suggests that the new periptychid genus from UCM locality 2011035 is closely related to Ampliconus antoni, while the new species of Conacodon appears closely related to C. cophater and C. entoconus, known from middle – late Puercan strata at several localities in the Western Interior. Additionally, the phylogenetic analysis suggests that the genus Conacodon may be paraphyletic. If prior estimates of an early Puercan age for UCM locality 2011035 are correct, then the occurrence of two new periptychid taxa suggest that mammalian diversity is higher than previously thought for the earliest Paleocene.