You Can't Run, but You Can Hide: The Skeleton of the Sand‐Swimmer LizardCalyptommatus leiolepis(Squamata: Gymnophthalmidae)

Abstract

Squamates exhibit a vast diversity of body plans, which directly determines habitat use and preference. Here the skeleton of the sand-swimmer burrower gymnophthalmid, Calyptommatus leiolepis, is analyzed to investigate how its peculiar fossorial locomotion affects its osteology. Calyptommatus leiolepis is a limb-reduced, short-intermediate tailed lizard. Although there are other studies on its general anatomy, we performed a detailed description of its skeleton. Using high-resolution computer tomography, each bone element within the skeleton was digitally segmented and a detailed description rendered. Anatomical features related to burrowing include the head having a shovel-like snout with a well-developed horizontal soft tissue ridge, nasal cartilages that exclude sand from the nostrils, reduced eyes covered by a brille, lack of forelimbs, extreme reduction of hind limbs, and imbricated scales among others. The genus Calyptommatus has unique features such as a triradiate jugal (with digit-like posterior projections), a reduced pectoral girdle and forelimbs, parasternal processes that interconnect the ribs, and a single digit in the hind limbs. When comparing this species with other gymnophthalmid lizards including, fossorial species, it is clear that Calyptommatus exhibits the highest number of structural modifications within the family. Despite its specialized morphology, it still retains characters that link this genus to other members of Gymnophthalmidae when included in a phylogeny based solely on phenotypic data. Anat Rec, 303:1305-The Order Squamata (lizards, amphisbaenians, and snakes), with more than 10,000 extant species recognized (Uetz et al., 2019), includes a diversity of body forms ranging from the typical lizard morphotype with welldeveloped limbs to the elongated limbless form of snakes (Bradley et al., 2008;Vitt and Caldwell, 2014). Although the snakes constitutes 35.5% (3,763 extant species) of the total number of squamate species, the percentage of snake-like squamates is much higher because body elongation and limb/attenuation/loss has appeared in several

Comparative anatomy of the middle ear in some lizard species with comments on the evolutionary changes within Squamata

“…Lizards occupy a wide diversity of habitats (e.g., terrestrial, arboreal, saxicolous, fossorial, sand dwellers, semi-aquatic, and aquatic), and for this reason, it is expected that they exhibit significant variation in their middle ear structure depending on the way and medium through which they perceive sounds. As anticipated, according to the literature, the columella bone is a constant element with an uniaxial organization, although differs in shape and proportions (ranging from being long and thin as in Tupinambis nigropunctatus = Tupinambis teguixin ( Jollie, 1960 ) to short and stumpy as in Calyptommatus leiolepis ( Holovacs et al, 2020 )). The extracolumella on the other hand, shows more significant variation in the number and shape of its processes ( Fig.…”

Phylogenetic history influences convergence for a specialized ecology: comparative skull morphology of African burrowing skinks (Squamata; Scincidae)

“…Segmentation of individual ossicles was challenging, as they were rarely distinct. This may be an artifact of the scan or may indicate a high level of fusion, as seen in other burrowers [ 53 ].…”

“…Basicranial sesamoids are found in many squamate families, including Scincidae, although previous examination of an acontine did not find any [ 6 , 71 ]. They are typically small in non-fossorial squamates, but can be large in burrowers to provide a larger attachment site for the longus colli muscle [ 53 , 71 ]. A larger longus colli muscle, which pulls the head down, may allow for the generation of greater forces for burrowing.…”

“…Our work shows that morphological specialization and convergence can occur through different pathways, even within a single family, adding to the literature on imperfect convergence and lineage-specific constraints [ 4 , 5 ]. The atlased species also contribute to a growing body of detailed skull morphology literature made possible by CT scanning [ 11 , 39 , 53 , 75 ] that will facilitate the characterization of other lizard skulls for phylogenetic and functional studies. By using both qualitative and quantitative methods, we gained a richer understanding of how phylogenetic history, ecology, and functional pressures influence morphology and showed that there are many ways to be a burrower.…”

Locomotion and palaeoclimate explain the re-evolution of quadrupedal body form inBrachymeleslizards

“…Other aspects of head shape may also affect burying performance. For example, the sandfish skink (Scincus scincus) and South American gymnophthalmid species that burrow in looser soil have pointy, shovel-like snouts [42,70,71]. We tested this idea and found that more snake-like species had more gently sloping snouts (electronic supplementary material, figure S2C), but that pointiness was unrelated to body form (electronic supplementary material.…”