Phylogenetic relationships among American badgers (Taxidiinae) and the evolution of the badger ecomorph

The American badgers (Taxidiinae) are medium-sized mustelid carnivorans with a complex dentition and fossorial lifestyle. Despite a fair representation in late Cenozoic deposits of North America, the taxidiine badgers do not have an extensive fossil record. Additionally, the phylogenetic relationships among Taxidiinae and Melinae (Eurasian badgers) have been a source of controversy. The first chapter presents the description of a new genus and species of taxidiine badger, Chamitataxus avitus, from the late Miocene Chamita Formation in Rio Arriba County, New Mexico. The skull of this new taxon is described in detail, facilitated by high-resolution X-ray computed tomography (CT), which provides non-destructive visualization of the internal morphology. Notably, the P4 of Chamitataxus does not exhibit the development of a medial shelf and hypocone observed in Taxidea and Pliotaxidea. This is evidence for the acquisition of a P4 medial shelf and hypocone independent from that of meline badgers. The second chapter addresses the relationships among "badgers" by way of a phylogenetic analysis of the mustelid carnivorans. The preferred analysis was run using the complete data matrix of 82 morphological characters (craniodental, post-cranial, and soft tissue) and 37 mustelid genera (both fossil and Recent). A total of 24 equally most parsimonious trees were recovered, each with a length of 311 steps. The preferred tree does not support a monophyletic "badger" clade. Taxidiinae and Mellivora are sister taxa, while Melinae is the sister taxon of Lutrinae. The label "badger" is actually an ecomorphic term, for it has been applied to mustelids that are fossorial omnivores, sharing similar morphologies but not a recent common ancestor.Geological Science