Abstract: A new species of the mesonychian mammal genus Hapalodectes is described from the Gashatan (late Paleocene) site of Subeng in Nei Mongol (Inner Mongolia). This is the first Paleocene record ofHapalodectes from China, and the second Gashatan species of Hapalodectes to be recorded from Asia. Available phylogenetic and biostratigraphic evidence supports an Asian origin for Hapalodectes (and Hapalodectidae). Hapalodectes apparently dispersed across Beringia coincident with PETM warming to colonize North America, thereby conforming to the “East of Eden” biogeographic pattern. Reconstructing the historical biogeography of Hapalodectes is facilitated by its restricted (i.e., non-European) geographic distribution. “East of Eden” dispersal such as that shown by Hapalodectes qualifies as an excellent example of geo-dispersal, whereby a major perturbation of the physical environment allows multiple clades to exhibit similar biogeographic and phylogenetic patterns. Purported examples of intercontinental mammalian dispersal at or near the Paleocene−Eocene boundary that conflict with the “East of Eden” pattern are critically examined and found to be wanting. The “East of Eden” biogeographic pattern adequately explains mammalian faunal turnover and Laurasian mammalian biogeography during the PETM.

摘要： 记述了发现于内蒙古苏崩晚古新世格沙头期的中兽类软食中兽Hapalodectes属的一个新种。这是软食中兽在中国古新世地层中的首次发现，也是亚洲格沙头期第二种软食中兽。已有的系统学和生物地层学证据支持软食中兽属和软食中兽科(Hapalodectidae)亚洲起源的观点。软食中兽显然是在古新世−始新世极热事件(PETM)期间通过白令陆桥扩散到北美大陆的，因而符合“东方伊甸园”学说中的生物地理格局。软食中兽有限的(即非欧洲的)地理分布使得我们可以重建该属生物地理学历史。如同软食中兽一样的“东方伊甸园”式的扩散模式，可以看作是大的环境变化事件导致多个支系产生相似的系统学和生物地理学分布格局的生物地理扩散机制。严格地检查了所谓的在古新世−始新世界线上或其附近的与“东方伊甸园”模式相矛盾的大陆间哺乳动物扩散事例，结果发现这些例子都是不可靠的。“东方伊甸园”生物地理学说充分解释了PETM时期哺乳动物群更替以及劳亚古陆哺乳动物地理分布格局的成因。