Limb and tail lengths in relation to substrate usage in Tropidurus lizards.

A close relationship between morphology and habitat is well documented for anoline lizards. To test the generality of this relationship in lizards, snout-vent, tail, and limb lengths of 18 species of Tropidurus (Tropiduridae) were measured and comparisons made between body proportions and substrate usage. Phylogenetic analysis of covariance by computer simulation suggests that the three species inhabiting sandy soils have relatively longer feet than do other species. Phylogenetic ANCOVA also demonstrates that the three species inhabiting tree canopies and locomoting on small branches have short tails and hind limbs. These three species constitute a single subclade within the overall Tropidurus phylogeny and analyses with independent contrasts indicate that divergence in relative tail and hind limb length has been rapid since they split from their sister clade. Being restricted to a single subclade, the difference in body proportions could logically be interpreted as either an adaptation to the clade's lifestyle or simply a nonadaptive synapomorphy for this lineage. Nevertheless, previous comparative studies of another clade of lizards (Anolis) as well as experimental studies of Sceloporus lizards sprinting on rods of different diameters support the adaptive interpretation.