MORPHOLOGICAL CONVERGENCE ACROSS LIMB-REDUCED LIZARDS FROM THREE CONTINENTS: AUSTRALIA, ASIA AND AFRICA
Thennakoon Mudalige S., Supuni
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Evolution of a serpentiform body where the body is elongated and the limbs are attenuated is a common process among squamates (lizards and snakes). Morphological convergence of this body shape might be linked to habitat preference and could be a response their peculiar locomotion mode. Although evolution of body elongation has been studied extensively, its effects on the skull anatomy remains largely unknown. Here, I quantify the skull morphological convergence of limb-reduced lizards from three continents using geometric morphometrics. Twenty seven morphological landmarks associated with the skull were studied in dorsal, lateral, and ventral views using highresolution CT scans of the heads of surface active, limb-reduced Paradelma orientalis (family Pygopodidae) endemic to the Australian mainland, New Guinea and the neighbouring islands; semi-fossorial Acontias percivali and Acontias meleagris (family Scincidae, subfamily Acontinae) endemic to Sub Saharan Africa; and semi-fossorial Nessia burtonii and Nessia monodactyla (family Scincidae, subfamily Scincinae) endemic to Sri Lanka. The level of similarity of the skulls of limb-reduced lizards was quantified using three-dimensional geometric morphometric analysis, including fully limbed and limb-reduced counterparts. PC1 versus PC2 reflected that the distribution of taxa follows a gradient that describes their nature of limbs (fully limbed, limb-reduced, limbless), which is correlated with their habitat preference (surface active, semi-fossorial and fossorial). PC1 versus PC3 also distinctly segregated the limbed and limb-reduced taxa with zero overlap. The pPCA produced visible clusters that correspond to groups of phylogenetically related taxa further proving the embedded phylogenetic structure in the morphological data set. Semi-fossorial taxa Acontias percivali and Acontias meleagris clustered together in the PCA and pPCA plots with semi-fossorial Nessia burtonii and Nessia monodactyla. Paradelma orientalis diverged from Acontias and Nessia species in both morphological and phylo-morphological spaces. This supports the morphological convergence of Acontias percivali and Acontias meleagris of Sub Saharan Africa with Nessia burtonii and Nessia monodactyla of Sri Lanka.