Systematics and Phylogeny of Paleocene-Eocene Nyctitheriidae (Mammalia, Eulipotyphla?) with Description of a new Species from the Late Paleocene of the Clarks Fork Basin, Wyoming, USA

Abstract

Nyctitheriidae is a diverse group of small, insectivorous mammals from the Paleogene of Asia, North America, and Europe that have alternately been linked to Eulipotyphla (shrews, moles, hedgehogs, solenodons), Euarchonta (primates, tree shrews, dermopterans), or Chiroptera (bats). Even intrafamilial relationships are poorly understood, resulting in ambiguity regarding morphological character polarity critical for evaluating supraordinal relationships and paleobiogeographic patterns. To help address this issue, we performed a cladistic analysis of 51 North American, European, and Asian nyctitheriid species, including a new nyctitheriid, Plagioctenodon thewisseni sp. nov. from the late Paleocene of Wyoming, using 66 characters derived from dental morphology. Although the oldest nyctitheriids are found in North America, the resulting most-parsimonious cladograms support an Asian origin of the family with dispersal into North America by the early Paleocene. Among North American and European groups, the subfamilies Nyctitheriinae and Amphidozotheriinae, and the genera Leptacodon and Saturninia are not monophyletic and require future study and revision. The multi-species genera Nyctitherium, Plagioctenodon (including P. thewisseni), Plagioctenoides, Cryptotopos, and Euronyctia are found to be monophyletic, whereas Wyonycteris is paraphyletic, having Pontifactor bestiola nested within it. The earliest known European nyctitheriids (Leptacodon nascimentoi, Placentidens lotus, Plagioctenodon dormaalensis, Wyonycteris richardi) appear in the early Eocene and are each found in an otherwise strictly North American clade consisting of either solely Paleocene or a combination of Paleocene and Eocene taxa, suggesting at least four earliest Eocene dispersals between North America and Europe.