Osteology of Lophiodon Cuvier, 1822 (mammalia, perissodactyla) and its phylogenetic implications

Lophiodon is the best-known member of the Lophiodontidae, a family of Eocene Eurasian perissodactyls, in terms of its skull and postcranial skeleton. Previous studies have allied Lophiodontidae with either Tapiroidea or Chalicotherioidea. This study describes the cranial and postcranial osteology of Lophiodon with an emphasis on characters pertaining to the phylogenetic position of lophiodontids. Although cranial and postcranial remains of Lophiodon are known from European faunas, the skull and postcranial skeleton have not been well studied, and few non-dental characters have been used to investigate the relationships of this genus to other perissodactyls. Lophiodon displays a mosaic of cranial and postcranial features that could be interpreted as possible synapomorphies uniting it with either tapiroids or chalicotherioids. Data collected from these studies were incorporated into a phylogenetic analysis of a variety of perissodactyl taxa scored for characters of the skull, postcranial skeleton, and dentition. These data indicate that lophiodontids, as represented by Lophiodon, are the sister-taxon to Ceratomorpha (Tapiroidea plus Rhinocerotoidea). Chalicotherioids are paraphyletic and placed in a clade with palaeotheriids and brontotheres, a result that may be due to superficial similarities of the dentition. Thus, lophiodontids still belong in the Tapiromorpha, but cranial and postcranial evidence does not support a special relationship with either tapiroids or chalicotherioids. Unlike previous studies, the results also do not support a monophyletic Equoidea (Palaeotheriidae plus Equidae).