Morphological Adaptations of the Sand-Swimmer Lizard Calyptommatus leiolepis (Squamata: Gymnophthalmidae)

Squamates exhibit a vast diversity of body plans. These body plans are directly affected by the habitat and how they interact within it. A common occurrence within this group is the reduction of hind and forelimbs as well as body elongation. In this study, the axial and appendicular skeleton of the fossorial gymnophthalmid, Calyptommatus leiolepis, is analyzed to determine how its mode of locomotion affects its osteology. C. leiolepis is a fossorial sand swimmer with a moderately elongated body and a short tail. With this locomotor specialty it is important to determine the specific features that result. Current descriptions of closely related species indicate that there is a level of detail that is still required. Using high-resolution computer tomography (HRCT) each bone element within the skeleton was digitally segmented and a detailed description rendered. Key features related to the fossorial sand swimming nature of C. leiolepis include the head exhibiting a wide array of adaptations such as a shovel-like snout with a well-developed horizontal cartilaginous rim, nasal cartilages that produce a sand-guard to protect the nostrils, reduced eyes covered by a brille, lack of forelimbs, extreme reduction of hindlimbs, and imbricated scales among others. In addition to the autapomorphic features of Calyptomatus such as the cartilaginous labial rim, a triradiated jugal (with digit-like projections), a reduced pectoral girdle with upper limb, parasternal processes that reinforce the ribcage, and a single digit in the lower limbs. When comparing this species with other gymnophtalmid lizards including fossorial species, it is clear that Calyptomatus exhibits the higest number of structural modifications within the family. Despite its specialized morphology, it still retains characters that link this genus to other members of Gymnophtalmidae when included in a phylogeny based on phenotic data.