Hapalodectidae

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 of Hapalodectes 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 PKTM 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

Abstract: A lower jaw of the mesonychian Hapalodectes is reported from Nongshanian sediments (Upper Doumu Formation; middle Paleocene) of the Qianshan Basin (Anhui Province, China). The fragmentary mandible is only the third specimen of Hapalodectidae discovered in Paleocene deposits, and the first in south east China; it is moreover the oldest, the two other specimens having been found in Gashatan (late Paleocene) localities. The premolars and molars of the new fossil are morphologically similar to Hapalodectes dux (late Paleocene of Mongolia), which has been considered to be the most primitive hapalodectid, but their relative proportions recall H. paleocenus and the Eocene Hapalodectes species. As a result, the fossil described herein appears to be different from the other previously described species of Hapalodectes in being morphologically intermediate between H. dux and the other Hapalodectes species, notably the Bumbanian Hapalodectes hetangensis and H. huanghaiensis from China; it is thus identified as a new species, Hapalodectes lopatini (possibly a male individual). Its discovery is important because it sheds light on the initial radiation of hapalodectids. The presence of one primitive hapalodectid in Mongolia previously suggested the Mongolian Plateau as the centre of origination of this carnivorous family, but the discovery of H. lopatini in older sediments from south-east China challenges this hypothesis. In the earliest Eocene, Hapalodectes dispersed from Asia to North America; this event being part of the ‘East of Eden’ dispersals. This event resulted in the geographical separation of two distinct Hapalodectes groups, in North America and south-eastern China respectively.