Shearing Mechanics and the Influence of a Flexible Symphysis During Oral Food Processing in Sphenodon (Lepidosauria: Rhynchocephalia)
Article first published online: 30 MAY 2012
Copyright © 2012 Wiley Periodicals, Inc.
The Anatomical Record
Volume 295, Issue 7, pages 1075–1091, July 2012
How to Cite
Jones, M. E.H., O'higgins, P., Fagan, M. J., Evans, S. E. and Curtis, N. (2012), Shearing Mechanics and the Influence of a Flexible Symphysis During Oral Food Processing in Sphenodon (Lepidosauria: Rhynchocephalia). Anat Rec, 295: 1075–1091. doi: 10.1002/ar.22487
- Issue published online: 14 JUN 2012
- Article first published online: 30 MAY 2012
- Manuscript Accepted: 5 APR 2012
- Manuscript Received: 28 JAN 2012
- BBSRC. Grant Numbers: BB/E007465/1, BB/E009204/1, BB/E007813/1 [to S.E.E. (UCL), M.J.F. (University of Hull), P.O. (Hull York Medical School)]
The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil rhynchocephalians suggests that it was once more widespread. Anat Rec, 2012. © 2012 Wiley-Periodicals, Inc.