Abstract

• Yinseik area occupies Obogon Formation (Middle Miocene) and Irrawaddy Formation (Late Miocene to Early Pleistocene). The dominant lithology of Obogon Formation is an alternation of yellowish brown- to buff-colored, fine to medium-grained, thin-bedded sandstone and light gray to bluish gray clay and shale with fine- to medium-grained sandstone. Irrawaddy Formation is mainly composed of thick bedded to massive, medium to coarse-grained, light gray to light brown, concretionary sandstone with cross stratification in the lower part and massive, medium to coarsegrained, light gray to yellowish brown, gritty to pebbly, incoherent sandstone interbedding with siltstone in upper part. The sediments of Irrawaddy Formation in research area yields the fossilized remains of primate (Khoratpithecus sp), carnivores, Anthracothere (Merycopotamus sp.), tragulid, wild boar (Tetraconodon sp. and Propotamochoerus sp.), bovids, rhinoceros (Rhinoceros sp.), horse (Hipparion sp.), elephant (Stegolophodon sp.) and crocodile (Gavialis sp.) which occur in the sediments of Irrawaddy Formation. The present faunal assemblage suggests the existence of forest/woodland adapted animals in Yinseik area in the geological past. Occurrence of crocodile (Gavialis sp.) and extinct river shark (Glyphis sp.) in this area supports the presence of riverine environment. Present day’s environmental conditions in Central Myanmar are characterized by a subtropical semi−arid climate especially in most parts of Mandalay and Magway Regions. The vegetation of this region is dominated by open shrub lands and grasslands. Therefore, the occurrence of forest dwelling mammals in present area contributes to the implication that the Late Miocene paleoenvironment of Yinseik area was drastically different from the present day’s conditions in central Myanmar.