Data from: The first species of Hapalodectes (Mesonychia, Mammalia) from the middle Paleocene of China (Qianshan Basin, Anhui Province) sheds light on the initial radiation of hapalodectids

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.

本文报道了一件采自中国安徽省潜山盆地农山阶沉积物（上窦村组（Upper Doumu Formation）；中古新世（middle Paleocene））的中爪兽类（Mesonychia）软食中兽属（Hapalodectes）下颌骨化石。
该件残缺下颌骨是古新世（Paleocene）地层中发现的第三件软食中兽科（Hapalodectidae）标本，同时也是中国东南部首例该科化石；此外，它还是目前已知最古老的软食中兽科标本——另外两件标本均产自加沙坦阶（Gashatan，晚古新世（late Paleocene））化石点。
该新化石的前臼齿与臼齿在形态上与Hapalodectes dux（蒙古国晚古新世（late Paleocene）物种，曾被认为是最原始的软食中兽科类群）相似，但其相对比例却更接近H. paleocenus以及始新世（Eocene）的软食中兽属物种。
据此，本文所描述的这件化石与此前已发表的其他软食中兽属物种存在显著差异，其形态介于H. dux与其他软食中兽属物种之间，尤其是产自中国本巴阶（Bumbanian）的Hapalodectes hetangensis与Hapalodectes huanghaiensis；因此该标本被鉴定为一新种：Hapalodectes lopatini（可能为雄性个体）。
该发现具有重要科学意义，它为揭示软食中兽科的早期辐射演化提供了关键线索。此前学界曾基于蒙古国发现的原始软食中兽科物种，提出蒙古高原是该食肉兽类科的起源中心，但在中国东南部更古老沉积物中发现的H. lopatini化石，对这一假说提出了挑战。
在始新世最早期（earliest Eocene），软食中兽属从亚洲扩散至北美洲；这一事件属于“伊甸园以东（East of Eden）”生物扩散事件的组成部分。此次扩散事件导致软食中兽属的两个演化支系分别在北美洲与中国东南部实现了地理隔离。