鸟类起源研究取得重大进展

鸟类起源于兽脚类恐龙的假说得到了广泛承认,但鸟类起源研究方向依然存在许多薄弱环节,主要包括鸟类手指同源问题、兽脚类分异时间框架问题以及羽毛起源和早期演化的一些问题。我们近年来在这些问题上取得了一系列重要进展。化石资料显示,兽脚类恐龙在向鸟类进化当中,其外侧两指退化;而现代发育学证据表明,鸟类手指是两侧退化,保留了中间3指。我们通过研究新疆侏罗系地层中发现的泥潭龙,提出了一种外侧和两侧退化模式结合的新假说。该假说可以解释古生物学与发育学资料之间的矛盾。我们报道的一件产自辽宁中上侏罗统髫髻山组的近鸟龙化石,代表了早于始祖鸟的带羽毛的物种,我们提出了包括鸟类在内的主要兽脚类恐龙类群出现于中侏罗世的一个快速演化事件,解决了有关鸟类兽脚类恐龙起源假说的时间悖论问题。我们报道了在北票龙化石中发现的一种新的原始羽毛类型,给出了发育学解释,推测羽毛起源的时间可能在三叠纪中期,对于羽毛起源和早期演化研究具有重要意义。

Recent Advances in Avian Origin Research

It has been widely accepted that birds are descended from theropod dinosaurs,but a number of issues remain poorly understood or highly debated,including the homologies of the avian manual digits,the early evolution of the major groups of derived theropods,and the origin and early evolution of feathers. Recently we made significant advances in these research areas. Theropods have traditionally been assumed to have lost manual digits from the lateral side inward,which contradicts many developmental studies indicating II-III-IV identities for the three manual digits of the birds. Based on new information from a basal ceratosaur from the Late Jurassic of Xinjiang,we proposed a new evolutionary scenario that can solve this problem. The early evolution of the major groups of derived non-avialan theropods is still not well understood,mainly because of their poor fossil record in the Jurassic. A well-known result of this problem is the ‘temporal paradox’ argument that is sometimes made against the theropod hypothesis of avian origins. We reported recently a theropod specimen from the Upper Jurassic Tiaojishan Formation of Liaoning,which represents the earliest known feathered species. This new find refutes the ‘temporal paradox’ and provides significant information on the temporal framework of theropod divergence. All described feathers in nonavian theropods are composite structures formed by multiple filaments. We reported recently a feather type which is represented by a single filament and thus corresponds to the earliest known stage predicted by developmental modles of the origin of feathers.