The evolution of the old world proboscieeans during the late Neogene.

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In order to illuminate the impact of the late Neogene climatic change on the proboscidean evolution in the realm of the Old World 1) the phylogenetic relationship among the late Neogene probosideans, mainly early elephants, stegdons and sinomasotodons and 2) the grazer /browser habit in those proboscideans are investigated. The new finding of the early proboscideans from the Nakali, Kenya, Middle Awash Ethiopia, Nakhon. Ratchasima, and Myanmar, confirmed the monophyly of the Stegodontidae negating previously supposed sister group relationship between stegodons and early elephants. In the Irrawaddy Group, nearly continuous evolutionary transition from the Stegolophodon to early stegodon is recognized. On the other hand, the earliest example of the elephantids are found from Nakali, which suggest close kinship with tetralophoodons.The function of the late Neogene gomphotheres, Anancus and Sinomastodon, suggest some of them accomplished the grazing function of their molars by means of the complication of the crown structure, and some of them dominate the early elephants and stegodonts in the grazer guild at the begging of the Pliocene. Later those grazing gomphotheres are declined, presumably defeated by the later elephants which has rapidly increased the efficiency of the horizontal shearing blade of the molar by means of the increase of the lophid number. Propalinal jaw movements appears to have facilitated such rapid evolution. On the other hand, stegodon remains extreme brachiodonty thorough out their history with the minor exception seen in the island dwarf forms.