Codd Jonathan R, Manning Phillip L, Norell Mark A, Perry Steven F
Faculty of Life Sciences, University of Manchester, Manchester M13 9PL, UK.
Proc Biol Sci. 2008 Jan 22;275(1631):157-61. doi: 10.1098/rspb.2007.1233.
In 1868 Thomas Huxley first proposed that dinosaurs were the direct ancestors of birds and subsequent analyses have identified a suite of 'avian' characteristics in theropod dinosaurs. Ossified uncinate processes are found in most species of extant birds and also occur in extinct non-avian maniraptoran dinosaurs. Their presence in these dinosaurs represents another morphological character linking them to Aves, and further supports the presence of an avian-like air-sac respiratory system in theropod dinosaurs, prior to the evolution of flight. Here we report a phylogenetic analysis of the presence of uncinate processes in Aves and non-avian maniraptoran dinosaurs indicating that these were homologous structures. Furthermore, recent work on Canada geese has demonstrated that uncinate processes are integral to the mechanics of avian ventilation, facilitating both inspiration and expiration. In extant birds, uncinate processes function to increase the mechanical advantage for movements of the ribs and sternum during respiration. Our study presents a mechanism whereby uncinate processes, in conjunction with lateral and ventral movements of the sternum and gastral basket, affected avian-like breathing mechanics in extinct non-avian maniraptoran dinosaurs.
1868年，托马斯·赫胥黎首次提出恐龙是鸟类的直接祖先，随后的分析在兽脚亚目恐龙中发现了一系列“鸟类”特征。骨化的钩突存在于大多数现存鸟类物种中，也出现在已灭绝的非鸟类手盗龙类恐龙中。它们在这些恐龙中的存在代表了将它们与鸟类联系起来的另一个形态特征，并进一步支持了在飞行进化之前兽脚亚目恐龙中存在类似鸟类的气囊呼吸系统。在此，我们报告了对鸟类和非鸟类手盗龙类恐龙中钩突存在情况的系统发育分析，表明这些是同源结构。此外，最近对加拿大鹅的研究表明，钩突是鸟类通风机制不可或缺的一部分，有助于吸气和呼气。在现存鸟类中，钩突的作用是增加呼吸过程中肋骨和胸骨运动的机械优势。我们的研究提出了一种机制，即钩突与胸骨和腹肋篮的侧向和腹侧运动相结合，影响了已灭绝的非鸟类手盗龙类恐龙中类似鸟类的呼吸力学。
