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Sphenodon chewing ability

From: Ben Creisler

Not strictly dino-related, but may be of interest:

Marc E.H. Jones, Paul O'higgins, Michael J. Fagan, Susan E. Evans &
Neil Curtis (2012)
Shearing Mechanics and the Influence of a Flexible Symphysis During
Oral Food Processing in Sphenodon (Lepidosauria: Rhynchocephalia).
Anatomical Record (advance online publication)
doi: 10.1002/ar.22487

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.

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