Cimolestids are a minor component of early Paleocene (Puercan) faunas of western North America. Here we report on cimolestids from the early Paleocene (middle and late Puercan; Pu2–3) of the Nacimiento Formation, San Juan Basin, New Mexico. New specimens of Puercolestes simpsoni include portions of the deciduous and lower dentition not previously known. We conclude that “Genus B” of Van Valen is probably conspecific with this taxon. Two new genera and species, Chacopterygus minutus and Betonnia tsosia, are from the Pu2 and Pu2–Pu3, respectively. One additional unnamed taxon is based on isolated teeth from Pu2–3 localities. A phylogenetic analysis indicates that Puercolestes simpsoni is sister to Cimolestes. Chacopterygus minutus, Betonnia tsosia, and the unnamed cimolestid form a polytomy that is sister to Procerberus. This resulting clade is sister to Batodon Maelestes. The results of this analysis suggest that P. simpsoni is descended from Cretaceous taxa of western North America. The origins of other early Paleocene cimolestids from either Asia or North America is equivocal. The species diversity of Cimolestidae in the Puercan of New Mexico and other Puercan localities of western North America is similar to that of latest Cretaceous (Lancian) faunas of the northern Rocky Mountain Region.
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Vol. 31 • No. 1