New anthracotheres (Cetartiodactyla, Mammalia) from the Paleogene of northeastern Vietnam: biochronological implications

摘要

Three new species of anthracotheres (one Anthracokeryx and two Bothriogenys) are described from the Na Duong coal deposits in northeastern Vietnam. These are the first representatives of the genera ever recorded from Vietnam, and they are morphologically close to species known in China, Thailand, Myanmar, and Egypt (Fayum). The material recently described from Na Duong is probably misattributed to Bakalovia and likely belongs to Elomeryx. The association in Na Duong of the three new species suggests an early late Eocene to middle late Eocene age for the fossiliferous sediments, which corresponds to a somewhat more precise and restricted time interval than the latest middle to early late Eocene age recently proposed. This also demonstrates that faunal exchanges were possible throughout South Asia and likely between South Asia and Africa during the Eocene period, and it questions the Miocene time of origination of the Na Duong Basin suggested by geological data.