The Palaeoryctidae are a group of small-bodied, likely insectivorous mammals known principally from the Paleocene and early Eocene (from approximately 65 to 53 Ma) of North America. Here we report on a new palaeoryctid from the early Eocene (early Wasatchian (Wa3) North American Land Mammal Age) Main Body of the Wasatch Formation, Washakie Basin, near Bitter Creek station in southwestern Wyoming, USA. Acerorcytes dulcis gen. et sp. nov. is unique among palaeoryctids in having a double-rooted P2 with a small anterior cusp, P3 with pronounced para- and metastylar cusps and a reduced but conspicuous metacone, P4 with a weakly developed metacone and an anteroposteriorly compressed protocone, and M1-2 with deep ectoflexus and a sharp metastylar blade. A phylogenetic analysis based on 32 dental characters of the nine known North American palaeoryctid species, including Aceroryctes dulcis, recovered eight equally parsimonious cladograms. Similar to prior studies, the analysis suggests that the genus Palaeoryctes is non-monophyletic, with Palaeoryctes cruoris and Aaptoryctes ivyi closely related. Aceroryctes dulcis is grouped with Ottoryctes winkleri and positioned in a more inclusive clade with Eoryctes melanus; the remaining palaeoryctid taxa, including Lainoryctes youzwyshyni, are part of an unresolved polytomy. These new findings indicate that early Eocene palaeoryctids were more diverse than previously thought, with genus richness during the early Eocene at least as great as that during the middle Paleocene.

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