中国北方上中新统的早期玛姆象属(Mammut)及其在玛姆象科(Mammutidae)分化和演化中的意义

玛姆象属是长鼻类玛姆象科这一重要类群的最终成员.虽然这一属在上新世的欧亚大陆和更新世的北美大陆广泛分布,它早期的进化历史却鲜为人知.报道了中国北方上中新统发现的斜脊玛姆象(相似种)(Mammut cf.M.obliquelophus)的新材料,包括一个几乎完整的幼年头骨,这些材料显示了玛姆象科的许多原始特征,因此很好地解释了玛姆象属形态特征的形成过程.斜脊玛姆象(相似种)具有强烈向两侧扩展的枕部,在门齿窝的基部具有收缩,这些特征与莫罗托始轭齿象(Eozygodon morotoensis)和广河豕脊齿象(Choerolophodon guangheensis)均具有相似性,后两者分别为玛姆象科与豕脊齿象科的早期代表.因此,玛姆象科与豕脊齿象科(Choerolophodontidae)具有近的亲缘关系,二者同位于象形类(Elephantimorpha)系统发育中的基部.支序分析支持了这一结论.

Early Mammut from the Upper Miocene of northern China,and its implications for the evolution and differentiation of Mammutidae

Mammut is the terminal taxon of the proboscidean group Mammutidae,which survived to the Late Pleistocene.Although this genus was widely distributed in the Pliocene of Eurasia and the Pleistocene of North America,little is known about its early evolution.Here,we report on Mammut cf.M.obliquelophus from the Upper Miocene of northern China based on new fossil material,including an almost complete juvenile cranium and other remains,which show many primitive features within Mammutidae and clearly demonstrate the morphological evolution of Mammut.The strongly laterally expanded lateral wing of the occiput and the presence of basal constriction of the incisive fossa display cranial similarity between Mammut cf.M.obliquelophus and both Eozygodon morotoensis and Choerolophodon guangheensis,early representatives of the Mammutidae and Choerolophodontidae,respectively,indicating the close relationship between these two groups:both of them are locatcd at the basal phylogenetic positions in Elephantimorpha.This result is further confirmed by a cladistic analysis.