Scale Microstructures of Pygopodid Lizards (Gekkota: Pygopodidae): Phylogenetic Stability and Ecological Plasticity

Abstract

The skin, as the interface of the body with the outside world, is directly exposed to the impacts of the environment. We have examined the microstructure of scale surfaces and the numerical distribution and morphology of skin sensory organs (SSO) in Australian limbless lizards of the family Pygopodidae. We have shown that the hairy sensory organs, as complex morphological structures, are a stable characteristic of the scale integument of pygopodids. This feature reflects their relationship to geckos and is shared homoplastically with some iguanian families (Dactyloidae, Leiosauridae, Opluridae, Chamaeleonidae). At the same time, scale micro-ornamentation as an elementary morphological structure is more plastic and, although the basic spinulate pattern is dominant, other variants occur on the scales of the serpentine body of pygopodids. We accept the spinules of MiO and the hairs of SSO as homologous structures at the cellular level since they are both derivatives of the Oberhäutchen cell surface. We propose to characterize the hair-bearing SSO of gekkotan and iguanian lizards as Oberhäutchen hairy sensory organs (ObHSO). Domination of SP MiO and presence of ObHSO in the integument of Gekkota and several families of Iguania, and sporadic occurrence of SP MiO in autarchoglossan taxa provide justification for regarding these characters as plesiomorphic. We characterize the high abundance (iterative state) of SSO in the scales of the head of pygopodids as representing the phenomenon of «overiteration», in which the phylogenetically established condition is enhanced by functional demands on the organism.