Li Zhiheng, Wang Min, Stidham Thomas A, Zhou Zhonghe
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.
Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China.
Nat Ecol Evol. 2023 Jan;7(1):20-31. doi: 10.1038/s41559-022-01921-w. Epub 2023 Jan 2.
The Cretaceous is a critical time interval that encompasses explosive diversifications of terrestrial vertebrates, particularly the period when the earliest-branching birds, after divergence from their theropod ancestors, evolved the characteristic avian Bauplan that led eventually to their global radiation. This early phylogenetic diversity is overwhelmed by the Ornithothoraces, consisting of the Enantiornithes and Ornithuromorpha, whose members evolved key derived features of crown birds. This disparity consequently circumscribes a large morphological gap between these derived clades and the oldest bird Archaeopteryx. The non-ornithothoracine pygostylians, with an intermediate phylogenetic position, are key to deciphering those evolutionary transformations, but progress in their study has been hampered by the limited diversity of known fossils. Here we report an Early Cetaceous non-ornithothoracine pygostylian, Cratonavis zhui gen. et sp. nov., that exhibits a unique combination of a non-avialan dinosaurian akinetic skull with an avialan post-cranial skeleton, revealing the key role of evolutionary mosaicism in early bird diversification. The unusually elongated scapular and metatarsal one preserved in Cratonavis highlights a breadth of skeletal plasticity, stemming from their distinct developmental modules and selection for possibly raptorial behaviour. Mapped changes in these two elements across theropod phylogeny demonstrate clade-specific evolutionary lability.
白垩纪是一个关键的时间间隔，涵盖了陆地脊椎动物的爆发式多样化，特别是最早分支的鸟类从兽脚亚目祖先分化出来后，进化出最终导致其全球辐射的典型鸟类形态结构的时期。这种早期的系统发育多样性被鸟胸类所掩盖，鸟胸类由反鸟亚纲和今鸟型类组成，其成员进化出了冠群鸟类的关键衍生特征。因此，这种差异界定了这些衍生类群与最古老的鸟类始祖鸟之间巨大的形态学差距。具有中间系统发育位置的非鸟胸类尾综骨鸟类是解读这些进化转变的关键，但已知化石的有限多样性阻碍了它们的研究进展。在这里，我们报告了一种早白垩世非鸟胸类尾综骨鸟类，朱氏克拉通鸟（Cratonavis zhui），它展示了一个非鸟类恐龙的不动头骨与鸟类颅后骨骼的独特组合，揭示了进化镶嵌性在早期鸟类多样化中的关键作用。克拉通鸟中保存的异常细长的肩胛骨和第一跖骨突出了骨骼可塑性的广度，这源于它们不同的发育模块以及对可能的捕食行为的选择。在兽脚亚目系统发育中这两个元素的映射变化表明了特定类群的进化易变性。
