O'Connor Jingmai K, Wang Xiaoli, Zheng Xiaoting, Hu Han, Zhang Xiaomei, Zhou Zhonghe
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
Institute of Geology and Paleontology, Linyi University, Linyi, Shandong 276000, China.
Curr Biol. 2016 Jan 11;26(1):114-9. doi: 10.1016/j.cub.2015.11.036. Epub 2015 Dec 31.
The most basal avians Archaeopteryx and Jeholornis have elongate reptilian tails. However, all other birds (Pygostylia) have an abbreviated tail that ends in a fused element called the pygostyle. In extant birds, this is typically associated with a fleshy structure called the rectricial bulb that secures the tail feathers (rectrices) [1]. The bulbi rectricium muscle controls the spread of the rectrices during flight. This ability to manipulate tail shape greatly increases flight function [2, 3]. The Jehol avifauna preserves the earliest known pygostylians and a diversity of rectrices. However, no fossil directly elucidates this important skeletal transition. Differences in plumage and pygostyle morphology between clades of Early Cretaceous birds led to the hypothesis that rectricial bulbs co-evolved with the plough-shaped pygostyle of the Ornithuromorpha [4]. A newly discovered pengornithid, Chiappeavis magnapremaxillo gen. et sp. nov., preserves strong evidence that enantiornithines possessed aerodynamic rectricial fans. The consistent co-occurrence of short pygostyle morphology with clear aerodynamic tail fans in the Ornithuromorpha, the Sapeornithiformes, and now the Pengornithidae strongly supports inferences that these features co-evolved with the rectricial bulbs as a "rectricial complex." Most parsimoniously, rectricial bulbs are plesiomorphic to Pygostylia and were lost in confuciusornithiforms and some enantiornithines, although morphological differences suggest three independent origins.
最原始的鸟类始祖鸟和热河鸟具有细长的爬行动物尾巴。然而，所有其他鸟类（尾综骨鸟类）都有一条缩短的尾巴，其末端是一个融合的结构，称为尾综骨。在现存鸟类中，这通常与一个称为尾羽球的肉质结构相关联，该结构固定尾羽（尾正羽）[1]。尾羽球肌在飞行过程中控制尾正羽的展开。这种操纵尾巴形状的能力极大地增强了飞行功能[2,3]。热河鸟类群保存了已知最早的尾综骨鸟类和各种各样的尾正羽。然而，没有化石能直接阐明这一重要的骨骼转变。早白垩世鸟类类群之间羽毛和尾综骨形态的差异导致了这样一种假说，即尾羽球与鸟胸类的犁形尾综骨共同进化[4]。一种新发现的燕鸟科鸟类，大前颌中华鸟（Chiappeavis magnapremaxillo）属及新种，保存了有力证据，表明反鸟类拥有空气动力学尾羽扇。在鸟胸类、孔子鸟类和现在的燕鸟科中，短尾综骨形态与清晰的空气动力学尾扇始终同时出现，这有力地支持了这样的推断，即这些特征与尾羽球作为一个“尾羽复合体”共同进化。最简约的情况是，尾羽球在尾综骨鸟类中是祖征，在孔子鸟类和一些反鸟类中丢失了，尽管形态差异表明有三个独立的起源。
