First report of the lower dentition of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the late middle Eocene Pondaung Formation, Myanmar

The anthracothere Siamotherium pondaungensis from the late middle Eocene Pondaung Formation in Myanmar was known only from its upper dentition. Recent field work in the Pondaung deposits has led to the discovery of a juvenile fragmentary mandible preserving d3–d4, m1–m2 and erupting p3–p4. The morphology, structure and dimensions of these lower teeth (including simple and bunodont lower premolars with weakly developed talonids, lower molar trigonids and talonids of similar width, entoconid that lacks a postectoentocristid and slightly distal to the hypoconid) confirm their attribution to S. pondaungensis which is now documented by its almost complete dentition, and further demonstrate that this species clearly differs from all known dichobunoids, including Pak­ kokuhyus lahirii. Siamotherium pondaungensis is one of the Pondaung anthracotheres for which most complete cranial and dental material is known, and a phylogenetic analysis supports the basalmost position of Siamotherium within the hippopotamoids.