A new lower jaw of Siamopithecus eocaenus from the Late Eocene of Thailand

We describe here a nearly complete lower jaw of Siamopithecus eocaenus from the Late Eocene of Peninsular Thailand. It displays several new characters , such as the symphysis, the horizontal branch, part of the vertical branch and most of its anterior dentition. The symphysis is nearly vertical and b ears most characteristics of that of derived anthropoids but is unfused. In cisors were nor preserved. A large canine, P/2 alveolus and P/3-M/3 were pr eserved. P/2 is rooted and reduced. The morphology of P/3 and P/4 is charac teristic of that of anthropoids, with an oblique position in the tooth row, a labially displaced anterior root of P/3 and P/4 and the presence of a li ngually developed metaconid on P/4. The premolars display a primitive stage of anthropoid evolution. This discovery confirms the anthropoid status of Siamopithecus, its attribution to the family Amphipithecidae and demonstrat es the importance of Asia in the evolution of anthropoid primates. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.