Bolting, bouldering, and burrowing: functional morphology and biomechanics of pedal specialisations in desert-dwelling lizards

Animals often move in a variety of complex habitats and they often exhibit morphological variation that can be explained, at least in part, by the habitat in which they live. The habitats of animals are often generally categorised based on dominant structures. Although this scheme can be fruitful, it ignores the intricacies of the microhabitat and the actual habitat utilisation of an animal. This is especially the case for desert habitats, which are often regarded as uniform and simple. Desert-dwelling lizards, however, occupy a range of structures in a desert including trees, rocks, and sand, and they have been noted as being a dominant form in almost all the warm deserts of the world. Along with this disparity in microhabitat, lizards often exhibit pedal specialisations, or modifications, that enhance a given behaviour (e. g., digging or running). Much work has examined the thermal influences on lizard biology, but pedal specialisations have not been discussed in an integrative and comprehensive way. Here, I review the pedal specialisations in desert-dwelling lizards and discuss their functional ramifications. I will also propose links between these specialisations/modifications and characteristics of habitat structure. Some of the pedal specialisations of desert-dwelling lizards include adhesive toe pads for climbing (geckos), toe fringes and webbed feet for maximising the surface area in contact with the substrate (sand-dwelling lizards), a multifunctional foot (sand-dwelling lizards), zygodactylus feet (chameleons), and claws (rock-dwelling lizards). Finally, I propose a frame-