The Phylogeny and Classification of Tapiromorph Perissodactyls (Mammalia)

Despite an excellent fossil record, the phylogeny of Perissodactyla is not well understood, in terms of both the relationships within Perissodactyla and the position of the Perissodactyla among the orders of mammals. This paper provides a phylogenetic analysis of one major perissodactyl lineage, the Tapiromorpha. This analysis combines a more comprehensive sampling of characters and taxa with rigorous tree-searching methods to create a new hypothesis of tapiromorph relationships. The phylogeny of tapiromorph perissodactyls is analyzed using 45 characters of the skull, postcranial skeleton, and dentition scored for 29 taxa, including three nontapiromorph outgroups. Phylogenetic taxonomic definitions are constructed for suprageneric taxa. According to the results of this analysis, the Chalicotherioidea cannot be unequivocally assigned to the Tapiromorpha, nor can Homogalax or Cardiolophus. Isectolophus, Tapiroidea, and Rhinocerotoidea are unequivocal members of the Tapiromorpha. Heptodon is included in a monophyletic Tapiroidea. Amynodontid rhinocerotoids come out as the sister group to rhinocerotids, and indricotheres do not fall within the Hyracodontidae. The results of this study provide further arguments that tapiromorphs (and putative tapiromorphs) may be important for understanding the ancestral morphology of Perissodactyla.