Gujaratia indica, the oldest artiodactyl (Mammalia) from South Asia: new dental material and phylogenetic relationships

Abstract

Diacodexeids are widely considered to be a paraphyletic group consisting of the oldest and most primitive artiodactyls that made their sudden appearance in all northern continents around the Palaeocene–Eocene boundary. In South Asia, the first record of artiodactyls is marked by the appearance of Gujaratia indica from the early Ypresian (∼55 Ma) Cambay Shale of the Vastan lignite mine, India, which is slightly younger than the oldest artiodactyls from Europe and North America. Here we describe new dental material of G. indica, documenting associated upper dentition, including P4, a new locus. Gujaratia (including G. pakistanensis and G. indica) is clearly distinct from all known diacodexeids in having the most triangular upper molars and lower molars with weaker paraconids. Cladistic analysis performed to assess the phylogenetic relationships of Gujaratia with other diacodexeids, dichobunoids, raoellids and pakicetids shows that Gujaratia is monophyletic while Diacodexis and Diacodexeidae are strongly polyphyletic. Gujaratia is found to be closer to the North American diacodexeids and D. gigasei and D. morrisi from Europe, which form a paraphyletic group. The European Diacodexis represents an unnatural grouping with D. antunesi being most closely related to a clade comprising dichobunids and homacodontids, and D. gazini and D. varleti occupying basal positions in a clade comprising raoellids and pakicetids. Dichobunidae is also recovered as a polyphyletic group whereas Homacodontidae is paraphyletic. Raoellids and pakicetids, long considered to be endemic to the Indian subcontinent, are monophyletic and without close affinities to Gujaratia, and appear to be more closely allied to some European dichobunoids, e.g., D. gazini, necessitating a reappraisal of current ideas about artiodactyl origins.