中国最原始的嵌齿象——意外嵌齿象(Gomphotherium inopinatum)在临夏盆地的发现兼论中国的嵌齿象(英文)

Gomphotherium inopinatum,a basal Gomphotherium species from the Linxia Basin,China,and other Chinese members of the genus

临夏盆地下中新统的甘池梁地点发现了一件残破下颌带有m2和m3齿列。在齿列前方,其水平支伸长,并且不向下转折或倾斜。下颌角位置较低。颊齿小,冠面结构特征原始。齿谷在前后方向宽度中等,副齿柱侧及主齿柱中心小尖不分裂,副齿柱中心小尖不发育。这些特征与哈萨克斯坦图尔盖地区早中新世的意外嵌齿象(Gomphotherium inopinatum)相同,应归为该种。这是该种在中国的首次报道,并且是中国发现的最原始的种。进一步讨论了中国的嵌齿象各种的系统关系。维曼嵌齿象(G.wimani)代表了一种在欧亚大陆东部发现的进步类型,可以与欧洲的施泰因海姆嵌齿象(G.steinheimense)相联系。间型嵌齿象(G.connexum)则似乎是属于真正的"狭齿嵌齿象类群",因为其与狭齿嵌齿象(G.angustidens)的颊齿具有相似性。亚似貘型嵌齿象(G.subtapiroideum)或许代表了一个与狭齿嵌齿象不同的分支,而陕西嵌齿象("G.shensiensis")则可能是其中的一种变异。

An incomplete right dentary retaining m2 and m3 was recovered from the upper Lower Miocene of Ganchiliang, in the Linxia Basin. The part of the corpus anterior to the molars is strongly elongated, but not inclined or deflected downward. The mandibular angle of the ramus is in a low position. The molars are small and morphologically primitive. The interlophids are moderately anteroposteriorly open. Clear indications of further subdivision are absent in the posttrite half lophids and in the pretrite central conules. The major characters of the partial dentary correspond to those of Gomphotherium inopinatum from the Lower Miocene of the Turgai region of Kazakhstan, and the new Ganchiliang specimen is accordingly referred to this species. This is the first report of G. inopinatum from China, and G. inopinatum in turn represents the most basal species of Gomphotherium so far known in the Chinese record. Among other Gomphotherium species known from China, G. wimani represents a derived east Eurasian form that appears to be closely related to the European species G. steinheimense. Gomphotherium connexum seems to be a member of the ＂G. angustidens group＂, given its strong morphological resemblance to G. angustidens. G. subtapiroideum may represent another evolutionary branch of the ＂G. angustidens group＂, distinct from G. angustidens. ＂G. shensiensis＂ may represent a variation of G. subtapiroideum.