Frillneck lizard morphology: Comparisons between sexes and sites

Large samples of frillneck lizards, Chlamydosaurus kingii, were measured from two sites approximately 150 km apart in the Northern Territory of Australia. Frill size increases linearly with SVL up to a SVL of 103 mm. At larger SVLs frill size continues to increase linearly, but with a greater slope. This inflection point corresponds to the SVL at which the gap between the two halves of the frill closes. The relationship between neck length and SVLZ is a simple line without an inflection point. Jaw length and head width show an allometric pattern that is similar to frill length, but the inflection point corresponds to a SVL of approximately 204 mm. The significance of this change in slope is unclear because this SVL does not correspond to any known ecological or morphological factors. Compared to females, male lizards have significantly larger frills, longer jaws, and wider heads for a given SVL. Males also have a longer frill for a given head width. Morphological differences exist between the two sites: at one site the frill length, jaw length, and dry season masses of large males are greater for a given SVL than those of large males at the other site, but at the second site the lizards of both sexes tend to have wider heads. The differences between the sexes with respect to frill and head sizes are consistent with the use of these structures for intraspecific displays, but the significance of the differences between the two sites is not known.