Bite-force performance and head shape in a sexually dimorphic crevice-dwelling lizard, the common chuckwalla [Sauromalus ater (= obesus)]

A. Kristopher Lappin, Paul S. Hamilton, Brian Sullivan

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


The Common Chuckwalla [Sauromalus ater (= obesus)] is a large, sexually dimorphic lizard with a flattened head that takes refuge from predators in rock crevices. Males use their relatively large heads to bite competing males during territorial fights and to restrain females during copulation. Flattened heads with an antipredator function (i.e. seeking refuge in crevices) and enlarged heads with intrasexual competition and reproductive functions suggest possible antagonism between selective pressures on head morphology in males. To examine this hypothesis, we performed a morphometric analysis and measured the bite-force performance of 49 adult chuckwallas. Males had disproportionately wider heads than females, but did not have deeper heads. Males bit with nearly four times the force of females, consistent with the notion of sexual selection for high bite force in males. Although constrained by crevice-wedging behaviour, head depth was a good predictor of bite force in both sexes. In males, however, osteological head width also was a good predictor of bite force. These results are consistent with the hypothesis that head shape in males is under antagonistic selective pressures, which may partly explain the pattern of head shape dimorphism. The disproportionately wide head of males may reflect anatomical modifications to enhance bite force in response to sexual selection in spite of presumed constraints on head shape for crevice-wedging behaviour.

Original languageEnglish (US)
Pages (from-to)215-222
Number of pages8
JournalBiological Journal of the Linnean Society
Issue number2
StatePublished - Jun 2006


  • Antagonistic selection
  • Bite force
  • Crevice-dwelling
  • Sexual dimorphism

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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