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.