张和兽的发现及其在哺乳动物进化中的意义

Zhangheotherium and the Phylogenetic Relationships of Modern Mammal Groups

        王元青(古脊椎动物与古人类研究所!北京100044)
        胡耀明(古脊椎动物与古人类研究所!北京100044)
        李传夔(古脊椎动物与古人类研究所!北京100044)

         张和兽;哺乳动物;进化

        辽宁西部发现的张和兽化石是目前世界上惟一一件对齿兽类的骨架 ,属鼹兽科 ,时代为早白垩世 (约 1 .2 5亿年前 )。它具有非兽类哺乳动物的原始特征和兽类哺乳动物的进步特征。系统发育分析表明 ,现生单孔类与其它现生哺乳动物———有袋类和有胎盘类之间没有很近的亲缘关系。现生哺乳动物听觉功能的真正发育和直立运动姿态都是在比张和兽更进步的兽类哺乳动物中演化形成的。

        Zhangheotherium, a spalacotheriid, from the Early Cretaceous of western Liaoning, northeastern China is the only known skeleton of Symmetrodonta. It possesses the primitive characters of non-therian mammals and the derived characters of therian mammals. Phylogentic analysis suggests that the living egg-laying monotremes is not closely related to the other two modern mammal groups, marsupials and placentals. The hearing capability and parasagittal posture of modern mammals were evolved in the therian mammals more advanced than Zhangheotherium.