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First published online November 28, 2008
Journal of Experimental Biology 211, 3908-3914 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.021345

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The functional significance of the lower temporal bar in Sphenodon punctatus

Vicky Schaerlaeken^1,*, Anthony Herrel^1,2, Peter Aerts¹ and Callum F. Ross³

¹ Laboratory of Functional Morphology, Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerpen, Belgium
² Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
³ Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA

^* Author for correspondence (e-mail: vicky.schaerlaeken{at}ua.ac.be)

Accepted 20 October 2008

One of the major conundrums in the evolution of vertebrate cranial design is the early loss and frequent redevelopment of the lower temporal bar in diapsids. Whereas it has been proposed that the reduction of the lower temporal bar allows for an increase in jaw adductor mass and bite force, this has never been tested experimentally. As the sole recent representative of the Rhynchocephalia, Sphenodon punctatus is different from other extant lepidosaurians in having a fully diapsid skull and in using translation to shear food rather than using the typical puncture-crushing of other lizards. In the present study, we show that S. punctatus has lower bite forces compared with extant lepidosaurians. Moreover, dissection of the jaw muscles of an adult S. punctatus shows that the mass of the external jaw adductor muscle is significantly smaller than that of lizards, probably accounting for the lower measured bite forces. An analysis of the transport cycles suggests a less efficient prey transport in S. punctatus compared with an agamid lizard of similar size in terms of handling time and number of cycles needed to crush similar prey. Modelling of biting in S. punctatus suggests a different role of the jaw adductor muscles during biting and a clear functional role for the lower temporal bar. Future finite element models may provide better insights into the function of the lower temporal bar in S. punctatus.

Key words: Sphenodon punctatus, lower temporal bar, feeding behavior, bite force, static bite model

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