The Wasatchian Wa-0 mammalian fauna from the Paleocene-Eocene Thermal Maximum (earliest Eocene) is reasonably well sampled in North America, but mammals of small body size are still poorly known. Here we describe a new species of the insectivore Didelphodus based on a cranial rostrum, both dentaries, and a nearly complete upper and lower dentition, all found by screen-washing. The new species, D. caloris, is the oldest species of the genus known in North America. It differs from later early Eocene Didelphodus in being substantially smaller, in having relatively simple premolars, and in having a more reduced M3 relative to preceding molars. Precursors of Didelphodus are not known with certainty, and the species D. caloris may be an immigrant to mid-continent North America. D. caloris is tentatively interpreted as a dwarfed form like other Wa-0 mammals because of its small size relative to the better-known successor species D. absarokae.
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RBINS Staff Publications 2023
