A new earliest Paleocene (Puercan) arctocyonid mammal from the Fort Union Formation, Great Divide Basin, Wyoming, and its phylogenetic position among early ‘condylarths’

A new arctocyonid ‘condylarth’, <i>Sigynorum magnadivisus</i> gen. et sp. nov., is described from a recently discovered earliest Paleocene (early Puercan) fauna from the China Butte Member of the Fort Union Formation in the Great Divide Basin, southern Wyoming. Based on a sample of 18 specimens (including 14 partial dentaries) whose combined dentitions represent the p2, p4 and m1–3, the new taxon appears most similar in size and molar morphology to the early Puercan arctocyonid <i>Oxyprimus erikseni</i>, but differs in its p4 morphology. To examine the relationship between <i>S. magnadivisus</i> and other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed, utilizing 23 taxa (including 21 ‘condylarth’ species and the outgroup taxa <i>Cimolestes</i> and <i>Gypsonictops</i>) and 73 dental characters. The resulting strict consensus tree of 248 steps confirms the close relationship between <i>S. magnadivisus</i> and <i>O. erikseni</i>. Interestingly, our phylogenetic analysis also suggests that Puercan Periptychidae is paraphyletic; the early Puercan periptychids <i>Mimatuta morgoth, Mimatuta minuial, Maiorana noctiluca</i> and <i>Auraria urbana</i> appear more closely allied with arctocyonid and hyopsodontid taxa, while other Puercan periptychids <i>Conacodon</i> spp., <i>Ampliconus browni, Alticonus gazini, Oxyacodon</i> spp. and <i>Mithrandir gillianus</i> fall into a separate monophyletic clade. This analysis is among the first to focus on a large set of Puercan ‘condylarth’ taxa across geographically widespread localities, and, with the addition of the new species from the Great Divide Basin, suggests that diversity among early Puercan ‘condylarths’ is higher than previously recognized. http://zoobank.org/urn:lsid:zoobank.org:pub:4BF2E9D5-1803-43E9-82FF-EC4723203A87