Helically arranged cross struts in azhdarchid pterosaur cervical vertebrae and their biomechanical implications

Cariad J Williams; Martino Pani; Andrea Bucchi; Roy E Smith; Alexander Kao; William Keeble; Nizar Ibrahim; David M Martill

doi:10.1016/j.isci.2021.102338

Helically arranged cross struts in azhdarchid pterosaur cervical vertebrae and their biomechanical implications

iScience. 2021 Apr 14;24(4):102338. doi: 10.1016/j.isci.2021.102338. eCollection 2021 Apr 23.

Authors

Cariad J Williams^{1

2}, Martino Pani³, Andrea Bucchi³, Roy E Smith¹, Alexander Kao^{4

5}, William Keeble⁶, Nizar Ibrahim¹, David M Martill¹

Affiliations

¹ School of the Environment, Geography and Geosciences, University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth, PO1 3QL, UK.
² Center for Paleontology, Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Forbes Natural History Building 1816 S. Oak Street, Champaign, IL 61820, USA.
³ School of Mechanical and Design Engineering, University of Portsmouth, Anglesea Building, Anglesea Road, Portsmouth PO1 3DJ, UK.
⁴ School of Engineering, University of Portsmouth, Portland Building, Portland Street, PO1 3DJ, Portsmouth, UK.
⁵ Elettra Synchrotron Trieste, Science Park, 34149 Basovizza TS, Italy.
⁶ Faculty of Technology, University of Portsmouth, Anglesea Building, Anglesea Road, Portsmouth PO1 3DJ, UK.

Abstract

Azhdarchid pterosaurs, the largest flying vertebrates, remain poorly understood, with fundamental aspects of their palaeobiology unknown. X-ray computed tomography reveals a complex internal micro-architecture for three-dimensionally preserved, hyper-elongate cervical vertebrae of the Cretaceous azhdarchid pterosaur, Alanqa sp. Incorporation of the neural canal within the body of the vertebra and elongation of the centrum result in a "tube within a tube" supported by helically distributed trabeculae. Linear elastic static analysis and linearized buckling analysis, accompanied with a finite element model, reveal that as few as 50 trabeculae increase the buckling load by up to 90%, implying that a vertebra without the trabeculae is more prone to elastic instability due to axial loads. Subsuming the neural tube into the centrum tube adds considerable stiffness to the cervical series, permitting the uptake of heavy prey items without risking damage to the cervical series, while at the same time allowing considerable skeletal mass reduction.

Keywords: Animal Morphology; Imaging Anatomy; Paleobiology; Paleontology.