New record of a haplocyonine amphicyonid in Early Miocene of Nei Mongol fills a long-suspected geographic hiatus

犬熊科(Amphicyonidae)的4个亚科(Amphicyoninae,Daphoeninae,Haplocyoninae和Temnocyoninae)中,Haplocyoninae(简齿犬熊亚科)和Temnocyoninae(剪切犬熊亚科)是两类比较特殊的、高度食肉化的姊妹群。Haplocyoninae仅出现在欧洲的晚渐新世到早中新世,而Temnocyoninae则局限在北美的早渐新世到早中新世。目前亚洲虽还没有记录,但新近纪的亚洲无疑是欧洲与北美之间迁徙途中的必经之路。因此本文记录的新材料既是意外发现又是意料之中。2015年我们在内蒙古中部早中新世敖尔班组下红层中首次发现一枚犬熊类的左上第一臼齿。这颗臼齿虽然零星,但非常特征,属Haplocyoninae或Temnocyoninae无疑,值得记述。该牙齿由于中间的收缩及原尖周边齿带的变宽而具有明显的哑铃型轮廓。另外其原尖上的前、后脊也几乎消失,形成一种原尖缩小而且孤立的形态。上述特征与欧洲早中新世的Haplocyonoides mordax(咬合似简齿犬熊)似乎最接近,但由于材料稀少敖尔班犬熊类与北美的Temnocyon percussor更为接近的可能也不能完全排除。如果上述判断正确的话,新发现的Haplocyonoides则是目前发现的少数几例早中新世从欧洲迁移到亚洲的种类之一。这一支系在亚洲有可能延续到中中新世的Gobicyon(戈壁犬熊)。

We place on the record a newly discovered amphicyonid （beardogs） upper molar from the Early Miocene Lower Red Mudstone Member of Aoerban Formation in central Nei Mongol. This molar is highly diagnostic of European haplocyonine or North American temnocyonine, two subfamilies of beardogs that have long been known in those continents but notably absent in Asia. The new molar is strikingly similar to Haplocyonoides mordax and Temnocyon percussor with its dumbbell-shaped M1 outline, reduced parastyle, isolated protocone by a surrounding cingulum, and extreme reduction of pre- and postprotocristae. Given the limited material at hand, we tentatively refer the new Chinese fossil to the European Haplocyonoides cf. H. mordax because of their similar size and age relationship. If this identification is correct, our new record thus fills a large gap in the geographic distribution of the haplocyonines and represents an excursion of this rare subfamily from Europe.