New remains of primitive ruminants from Thailand:: evidence of the early evolution of the Ruminantia in Asia

A new tragulid, Archaeotragulus krabiensis, gen. n. et sp. n., is described from the late Eocene Krabi Basin (south Thailand). It represents the oldest occurrence of the family which was previously unknown prior to the Miocene. Archaeotragulus displays a mixture of primitive and derived characters, together with the M structure on the trigonid, which appears to be the main dental autapomorphy of the family. We also report the occurrence at Krabi of a new Lophiomerycid, Krabimeryx primitivus, gen. n. et sp. n., which displays affinities with Chinese representatives of the family, particularly Lophiomeryx. The familial status of Iberomeryx is discussed and a set of characters is proposed to define both Tragulidae and Lophiomerycidae. Results of phylogenetic analysis show that tragulids are monophyletic and appear nested within the lophiomerycids. The occurrence of Tragulidae and Lophiomerycidae in the upper Eocene of south-east Asia enhances the hypothesis that ruminants originated in Asia, but it also challenges the taxonomic status of traguloids within the Ruminantia.