Department of Biological Sciences, CW 405 Biological Sciences Building, University of Alberta, Edmonton, AB, T6G 2E9, Canada.
Maastricht Science Programme, Faculty of Science and Engineering, Maastricht University, Maastricht, The Netherlands.
Commun Biol. 2023 Jan 17;6(1):3. doi: 10.1038/s42003-022-04301-z.
Vertebral ribs of the anterior thorax in extant birds bear bony prongs called uncinate processes, which improve the mechanical advantage of mm. appendicocostales to move air through the immobile lung and pneumatic air sacs. Among non-avian archosaurs, broad, cartilaginous uncinate processes are present in extant crocodylians, and likely have a ventilatory function. Preserved ossified or calcified uncinate processes are known in several non-avian dinosaurs. However, whether other fossil archosaurs possessed cartilaginous uncinate processes has been unclear. Here, we establish osteological correlates for uncinate attachment to vertebral ribs in extant archosaurs, with which we inferred the presence of uncinate processes in at least 19 fossil archosaur taxa. An ancestral state reconstruction based on the infer distribution suggests that cartilaginous uncinate processes were plesiomorphically present in Dinosauria and arguably in Archosauria, indicating that uncinate processes, and presumably their ventilatory function, have a deep evolutionary history extending back well beyond the origin of birds.
现存鸟类前胸的脊椎肋骨带有称为钩突的骨性分支，这些分支提高了附着肌和肋软骨移气动肺和气囊中空气的机械优势。在非鸟兽脚亚目恐龙中，现生鳄类具有宽阔的软骨钩突，可能具有通气功能。在一些非鸟兽脚亚目恐龙中，也保存有骨化或钙化的钩突。然而，其他化石恐龙是否具有软骨钩突尚不清楚。在这里，我们建立了现生恐龙类钩突与脊椎肋骨附着的骨骼学关联，并据此推断至少 19 个化石恐龙类群具有钩突。基于推断分布的祖先状态重建表明，软骨钩突在恐龙类中是原始存在的，甚至在主龙形类中也是如此，这表明钩突，以及可能其通气功能，具有深远的进化历史，可以追溯到鸟类起源之前很久。
