陕西嵌齿象与同心铲齿象同物异名考及铲齿象属一新种

Attributing“Gomphotherium shensiense”to Platybelodon tongxinensis,and a new species of Platybelodon from the latest Middle Miocene

铲齿象(Platybelodon)在中国北方中中新世的长鼻类中占据着主导地位。然而,对其头骨和颊齿形态学的研究并不充分,尤其是与嵌齿象属(Gomphotherium)的区别并没有仔细研究。重新研究了之前被鉴定为陕西嵌齿象(Gomphotherium shensiense)的一件较为完整的头骨。这件标本上牙无釉质带,吻部窄长,面部位置靠前且伸长,有一个很大的“鼻前斜坡”。这些形态特征不同于已知任何嵌齿象的头骨,但与铲齿象的原始类群,如同心铲齿象(P.tongxinensis)和达氏铲齿象(P.danovi)相吻合;臼齿也和同心铲齿象正型标本M3一样,具有四脊,齿脊间距离较宽,外轮廓弯曲,有白垩质型齿发育的倾向。据以上特征,将陕西嵌齿象归为同心铲齿象,两者为同物异名。另外,还从美国自然历史博物馆中亚考察队在中国通古尔地区采集的一批格氏铲齿象(P.grangeri)材料中鉴定出一个新种四脊铲齿象(Platybelodon tetralophus sp.nov.)。不同于格氏铲齿象和其他的种,四脊铲齿象的M2和m2有4个齿脊,是铲齿象中最进步的种;它只在通古尔组的最上部层位出现,即属于铁木钦(Tamuqin)动物群的Platybelodon Quarry地点和Wolf Camp Quarry地点。本研究工作是对中国铲齿象属的全面修订。

Platybelodon is the predominant proboscidean of northern China’s Middle Miocene.However,the cranial and cheek tooth morphologies are not clearly diagnosed.In particular,the differential diagnoses between Platybelodon and Gomphotherium have not been comprehensively examined.Here we restudied the cranium previously identified as Gomphotherium shensiense.The upper tusks lack an enamel band,the rostrum is long and narrow,the facial part is rostrally positioned,and a large“prenasal slope”is present.These characters are distinct from those of any species of Gomphotherium,but fit well with some primitive species of Platybelodon,i.e.,P.tongxinensis and P.danovi.The molars are also close to the type specimen of P.tongxinensis in the tetralophodont M3 with mesiodistally wide interlophs,curved outline,and a tendency of cementodonty.In this article,we synonymized Gomphotherium shensiense with P.tongxinensis.Moreover,we recognized a new species,Platybelodon tetralophus,from the P.grangeri material collected by the AMNH expedition in Tunggur region.Platybelodon tetralophus differs from P.grangeri and the other species in the tetralophodont M2 and m2,representing the most derived species within Platybelodon.It has only occurred in the uppermost horizon of the Tunggur Formation,i.e.,the Tamuqin Fauna(Platybelodon Quarry and Wolf Camp Quarry of AMHN).This work is a comprehensive amending of the genus Platybelodon.