The Cenozoic terrestrial faunas of northern Vietnam

Today, the Indochina region represents one of the global hotspots in biodiversity, especially with regard to continental flora and fauna. But the deep history of the continental ecosystems in this region remains spottily documented. Here we will focus on the Eocene and Miocene terrestrial faunas of northern Vietnam with a special emphasis on the late Eocene mammal assemblage of NaDuong. The NaDuong Basin is a small pull-apart basin formed during the Paleogene along the sinistral strike-slip Red-River Faults Zone in which lacustrine coal like sediments accumulated since at least the middle Eocene. These deposits yielded high biodiversity of fossil leaves, dipterocarp trees, mollusks, freshwater fishes, turtles, crocodiles (three taxa), and several well identified mammal taxa that all suggest a late middle to late Eocene age for the coal-bearing Na Duong Formation. Among mammals, anthracotheriids are the most diversified with at least 3 genera and 4 species. An indeterminate traguloid ruminant, and the rhinocerotid Epiaceratherium are also present in the fauna. The Eocene mammal faunas from Na Duong and Europe highlights the importance of Southeast Asia as a source region for trans-continental mammal dispersal along the northern Tethys margin, and also probably suggests episodic faunal exchanges with Africa. The mammal assemblage reinforces the hypothesis that Southeast Asia was an important source of Eocene immigrants, which eventually replaced most of the European Eocene endemic faunas, with a culmination at the `Grande Coupure’.