Pakkokuhyus and Progenitohyus (Artiodactyla, Mammalia) from the Eocene of Southeast Asia are not Helohyidae: paleobiogeographical implications

摘要

Pakkokuhyus and Progenitohyus are two genera of primitive artiodactyls from the Eocene of Southeast Asia that have been referred to the family Helohyidae. However, recent advances in the phylogeny and systematics of basal artiodactyls suggest that the status of several Asian forms should be reassessed. In that frame, reexamination of the few dental remains known for Pakkokuhyus and Progenitohyus indicates that they very probably do not belong to the Helohyidae but to the Dichobunidae. The dental structure of the alleged helohyid Gobiohyus from Asia also suggests that the attribution of this genus to the Helohyidae is questionable. In that context, the representatives of the family Helohyidae probably originated in North America during the Middle Eocene and were never involved in dispersals between Eurasia and North America, contrary to the diacodexeids and homacodontids. This further suggests that the systematics of basal artiodactyls from Southeast Asia should be carefully reassessed.