New species of the plesiadapiform Paromomys Gidley (Primates, Paromomyidae) from the Paleocene of southwestern Alberta, Canada

Paromomyidae are a taxonomically diverse family of archaic primates known principally from deposits of Paleocene and Eocene age in North America. While often numerically abundant in local mammalian faunas, the various paromomyid taxa are most often represented by isolated teeth and rare dentigerous cranial and dentary fragments. Accordingly, paromomyid interrelationships are on balance poorly understood, and this is especially true for early branching taxa. We report here on two new species of Paromomys—long considered the earliest diverging paromomyid—from Paleocene deposits in southwestern Alberta. Paromomys borealis sp. nov. and Paromomys ignis sp. nov. bear closest resemblance to Paromomys depressidens and Paromomys maturus, respectively, and represent the first occurrences of the genus in Canada. A phylogenetic analysis of all paromomyid species resulted in overall poor resolution. Paromomys was recovered as non-monophyletic—consistent with previous results—with species either in a polytomy or positioned at increasingly crownward positions. In contrast to previous hypotheses, the position of Paromomys as the earliest diverging paromomyid was rendered equivocal. Notably, two recently described species of Ignacius from the Canadian Arctic resolved as sister to Acidomomys to the exclusion of other paromomyids. The newly discovered species of Paromomys are known from a vanishingly small number of specimens, and paromomyid diversity and overall abundance declined markedly through the Tiffanian in Alberta; in contrast, plesiadapoids—generally rare in the Torrejonian—increased significantly in diversity and abundance during the same interval.