中部ミャンマーの上部新生界より産出した長鼻類化石の新標本について

抄録

Paleontological expeditions of the Late Cenozoic sediments as well as the reappraisal of the collections of proboscidean fossils kept at various institutes in Myanmar shed new lights on the diversity of the Late Cenozoic proboscidean of Myanmar. The proboscidean fossils of Myanmar can be roughly divided into the Middle Miocene assemblage and those younger than the Middle Miocene. The former includes the elements common to the Chinji Formation of Siwaliks, such as Prodeinotherium cf. pentapotaminae, Zygolophodon cf. metachinjiensis, Protanancus cf. chinjiensis, as well as three un-named species of endemic gomphotheres. Unfortunately, the latter three can't be described formally because they are currently housed in a temple as a part of private collections. The assemblage younger than the Middle Miocene is composed of anancine, sinomastodont, and stegodontids. Myanmar Anancus is similar to A. perimensis from India in the primitive dental structure, suggesting close connection between Indo-Pakistan area and Indochina. The Late Miocene age of Myanmar Sinomastodon fossils supports Asian origin of this genus. However, the early separation of Myanmar Sinomastodon from the Chinese one is suggested by the more derived dental features of the former than the penecontemporaneous Chinese Sinomastodon species. A huge number of stegodontid fossils from the Irrawaddy sediments represent one of the best records of the radiation of this taxon. Numerous molar fossils of Irrawaddy sediments exhibiting the spectrum of dental evolution of stegodontids, from primitive Stegolophodon to highly derived Stegodon. A Stegodon skull from the Upper Irrawaddy exhibits a quite dissimilar morphology to previously known Stegodon crania from the other region of Asia. However, their scientific value is hampered by their poor stratigraphic data. Continuous effort to collect stratigraphically controlled specimens, as well as developments of some new means (e.g. histology) to distinguish fragmentary dental materials at specific level are necessary for the improvement of the situation.