Deep reptilian evolutionary roots of a major avian respiratory adaptation

Yan-yin Wang*, Leon P. A. M. Claessens, Corwin Sullivan

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


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.

A newly discovered osteological correlate for structures associated with ventilatory muscle attachment indicates a deep evolutionary history of respiratory innovation within Archosauria.
Original languageEnglish
Article number3
Number of pages8
JournalCommunications Biology
Issue number1
Publication statusPublished - 17 Jan 2023


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