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A new arctocyonid ‘condylarth’,Sigynorum magnadivisusgen. 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 arctocyonidOxyprimus erikseni, but differs in its p4 morphology. To examine the relationship betweenS. magnadivisusand 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 taxaCimolestesandGypsonictops) and 73 dental characters. The resulting strict consensus tree of 248 steps confirms the close relationship betweenS. magnadivisusandO. erikseni. Interestingly, our phylogenetic analysis also suggests that Puercan Periptychidae is paraphyletic; the early Puercan periptychidsMimatuta morgoth, Mimatuta minuial, Maiorana noctilucaandAuraria urbanaappear more closely allied with arctocyonid and hyopsodontid taxa, while other Puercan periptychidsConacodonspp.,Ampliconus browni, Alticonus gazini, Oxyacodonspp. andMithrandir gillianusfall 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 [ABSTRACT FROM AUTHOR]