Early Pleistocene Javan rhinoceros from the Irrawaddy Formation, Myanmar

Abstract

We report dental fossils of Javan rhinoceros, Rhinoceros sondaicus (Mammalia, Perissodactyla, Rhinocerotidae), discovered from the upper part of the Irrawaddy Formation, the lower Pleistocene of central Myanmar. This is the first discovery of R. sondaicus from the Irrawaddy Formation, and these materials are possibly to be the oldest fossil record of this species in the world. The present materials consist of two fragmentary maxillae with M_1-3. They are referable to those of Rhinoceros sondaicus in having the following characteristics on the upper molars: moderately developed molar crochet, subhypsodonty, absence of the molar crista and antecrochet, absence of the protocone fold, absence of the metacone bulge on M_3, sinuosity of the ectoloph, strong molar parastyle fold, and deeper median valley than the posterior valley. The discovery of early Pleistocene Rhinoceros sondaicus in Myanmar fills geographical and chronological gaps between the late Miocene Gaindartherium (a probable ancestor of the genus Rhinoceros) from Indo-Pakistan and middle Pleistocene R. sondaicus from Java and Sumatra. It suggests that this species originated as early as early Pleistocene in continental Asia.