始新世後半における哺乳類相の変遷とポンダウン化石哺乳類相 (ミャンマー)

Abstract

We briefly review the primate-bearing Pondaung mammal fauna (Eocene, Myanmar). The age of the Pondaung fauna has been determined as latest middle Eocene based on the radiometric (fission-track) dates analyzed recently. The Pondaung fauna consists of six orders of mammals, including 22 genera and 29 species. Among the 22 genera, more than half (12 genera) are endemic to this fauna. Although both artiodactyls and perissodactyls are abundant, the former is less diversified in familial and generic numbers than the latter, but is slightly more dominant in collection size [in particular, Anthracotherium (Artiodactyla; Anthracotheriidae) has been most dominantly collected from the field]. This suggests the beginning of the radiation of artiodactyls and decline of perissodactyls in the later Eocene of southern East Asia. Among the Pondaung perissodactyls, brontotheres and amynodonts are dominant in the collection size. The paleoenvironment of the Pondaung fauna is estimated as subtropical/tropical forest with large rivers and patches of open areas near seashore. Among the mammalian genera of the Pondaung fauna, only eight genera were shared with other Eocene faunas of East Asia. On the other hand, the Pondaung fauna shares Anthracotherium with the late Eocene to Oligocene faunas of Europe, and the Pondaung species are more primitive than the European ones. The Pondaung rodent is probably assigned to very primitive phiomyid or anomalurid, both of which had been recorded only in the late Eocene and latter age of Africa/West Asia. These suggest faunal migration from southern East Asia to Africa/West Eurasia during the later Eocene. If the Pondaung primates are really assigned to primitive anthropoids, they might migrate to Africa/West Asia with anthracotheres and/or rodents.