Vertebral pneumaticity is correlated with serial variation in vertebral shape in storks. Issue 3 (26th September 2020)

• Record Type: Journal Article
• Authors: Moore, Andrew J.
• Is Part Of: Journal of anatomy. Volume 238:Issue 3(2021)
• Page Start: 615
• Page End: 625
• Publication Date: 2020-09-26
• Subjects: biomechanics -- Ciconiidae -- geometric morphometrics -- pneumaticity -- vertebrae; Anatomy -- Periodicals; 571.3
• DOI: 10.1111/joa.13322
• Languages: English
• ISSNs: 0021-8782

Abstract

ABSTRACT: Birds and their ornithodiran ancestors are unique among vertebrates in exhibiting air‐filled sinuses in their postcranial bones, a phenomenon called postcranial skeletal pneumaticity. The factors that account for serial and interspecific variation in postcranial skeletal pneumaticity are poorly understood, although body size, ecology, and bone biomechanics have all been implicated as influencing the extent to which pneumatizing epithelia invade the skeleton and induce bone resorption. Here, I use high‐resolution computed‐tomography to holistically quantify vertebral pneumaticity in members of the neognath family Ciconiidae (storks), with pneumaticity measured as the relative volume of internal air space. These data are used to describe serial variation in extent of pneumaticity and to assess whether and how pneumaticity varies with the size and shape of a vertebra. Pneumaticity increases dramatically from the middle of the neck onwards, contrary to previous predictions that cervical pneumaticity should decrease toward the thorax to maintain structural integrity as the mass and bending moments of the neck increase. Although the largest vertebrae sampled are also the most pneumatic, vertebral size cannot on its own account for serial or interspecific variation in extent of pneumaticity. Vertebral shape, as quantified by three‐dimensional geometric morphometrics, is found to be significantly correlated with extent of pneumaticity, with elongate vertebrae being less pneumatic than craniocaudally short and dorsoventrally tall vertebrae. Considered together, the results of this study are consistent with the hypothesis that shape‐ and position‐specific biomechanics influence the amount of bone loss that can be safely tolerated. These results have potentially important implications for the evolution of vertebral morphology in birds and their extinct relatives. Abstract : Birds are unique among living vertebrates in having air‐filled sinuses in their postcranial skeletons, a phenomenon called postcranial skeletal pneumaticity (PSP). The factors that account for serial and interspecific variation in PSP are poorly understood. Using micro‐CT scans of stork vertebrae and geometric morphometric methods, I show that vertebral shape is strongly correlated with PSP, supporting the hypothesis that locus‐ and shape‐specific biomechanics influence skeletal pneumatization.