JOURNAL OF MORPHOLOGY 274:845–858 (2013) A Comparative Analysis of the Post-Cranial Skeleton of Fossorial and Non-Fossorial Gymnophthalmid Lizards Juliana G. Roscito* and Miguel T. Rodrigues Departamento de Zoologia, Instituto de Biocieˆncias, Universidade de Sa˜o Paulo, Sa˜o Paulo, Brasil ABSTRACT Squamates are found in a wide range of is characterized by the presence of well-developed habitats and show a corresponding diversity of morpholo- limbs that act as the main propelling elements for gies that can often be correlated with locomotor mode. the body. However, in the snake-like morphotype, The evolution of a snake-like body form, frequently associ- usually seen in burrowing species and characterized ated with fossoriality, from a typical lacertiform morphol- by reduced limbs often in association with an elon- ogy involves changes in the morphology of vertebrae, gir- dles, and limbs; the changes are mainly manifested by the gated body, locomotion is primarily the result of reduction or loss of limbs and body elongation. In this undulating movements generated by the axial skele- study, we describe the axial and appendicular skeletons of ton (Wiens et al., 2006; Shine and Wall, 2008). six closely related gymnophthalmid species. Three of them Fossoriality and the associated morphological show a lizard-like morphology, with a four-digit forelimb changes for burrowing have evolved independently and a five-digit hindlimb, and the other three show a several times within squamates (lizards, ‘‘snakes’’ snake-like morphology associated with a burrowing habit, and ‘‘amphisbaenians’’; Wiens et al., 2006; Brand- with reduced limbs and a longer body in comparison to ley et al., 2008), and different degrees of body elon- the former three species. We show that vertebral morphol- gation and limb/girdle reduction can be observed ogy is similar among the six species, with the differences both in distantly-related groups as well as within being accounted for by an increase in the number of verte- brae and by the structural reduction of girdles and limbs the same genus (Lee, 1998; Wiens and Slingluff, in the snake-like species. Skeletal morphology provides 2001; Shapiro, 2002; Skinner et al., 2008). valuable information on locomotion type, physiology, diet, The South American Gymnophthalmidae (Estes and other biological features. The burrowing morphology et al., 1988) is an example of a clade where a usually involves accentuated reduction of girdle and limb snake-like morphology, i.e., an elongated body and elements, reflecting an undulating type of locomotion in reduced or absent limbs have evolved independ- which the limbs play little or no role in propelling the ently in a few lineages (Pellegrino et al., 2001; body; in contrast, well-developed limbs and girdles indi- Castoe et al., 2004). One such lineage is the Gym- cate a greater reliance on the limbs for body propulsion. nophthalmini, a monophyletic group comprised of Limb reduction is frequent among vertebrates, but many nine genera, Tretioscincus, Micrablepharus, Gym- different phenotypes are found in species exhibiting some kind of reduction, indicating that different mechanisms nophthalmus, Procellosaurinus, Vanzosaura, Psi- and evolutionary pressures may be involved in generating lophthalmus, Nothobachia, Scriptosaura, and the diverse morphologies. J. Morphol. 274:845–858, Calyptommatus (Pellegrino et al., 2001; Castoe et 2013. Ó 2013 Wiley Periodicals, Inc. al., 2004; Rodrigues and dos Santos, 2008). The KEY WORDS: Gymnophthalmidae; limb morphology; Additional Supporting Information may be found in the online limb reduction; fossoriality version of this article. Contract grant sponsor: Fundac¸a˜o de Amparo a` Pesquisa do INTRODUCTION Estado de Sa˜o Paulo (FAPESP); Contract grant sponsor: Conselho Nacional de Desenvolvimento Tecnolo´gico (CNPq). The morphology of the axial and appendicular skeletons is quite variable among reptilian saurop- JGR analyzed the data, conceptualized and drafted the manuscript; sids, and variation in form can often be correlated MTR participated in the coordination of the study and revised it with lifestyle (Losos, 1992; Gans and Fusari, 1994; critically giving important intellectual contributions. Losos et al., 1994, 1998; Benesch and Withers, *Correspondence to: Juliana G. Roscito; Departamento de Zoo- 2002). Of especial interest is locomotor mode, which logia, Instituto de Biocieˆncias, Universidade de Sa˜o Paulo, Rua do is the result of coordinated actions of both the axial Mata˜o, Sa˜o Paulo, SP, Brasil. E-mail: [email protected] and appendicular systems (Renous et al., 1998), and is ultimately related to the morphology of such sys- Received 20 October 2012; Revised 17 December 2012; tems. The association between morphology and loco- Accepted 18 January 2013 motion is easily perceived when comparing lizard- Published online 18 March 2013 in like and snake-like species: the former morphotype, Wiley Online Library (wileyonlinelibrary.com) usually associated with a ground-dwelling habitat, DOI 10.1002/jmor.20139 Ó 2013 WILEY PERIODICALS, INC. 846 J.G. ROSCITO AND M.T. RODRIGUES Fig. 1. Gymnophthalmini species analyzed in this study. A. Procellosaurinus tetradactylus. B. Vanzosaura rubricauda. C. Psilophthalmus paeminosus. D. Nothobachia ablephara. E. Scrip- tosaura catimbau. F. Calyptommatus nicterus. former six genera have a lizard-like body form MATERIAL AND METHODS with well-developed limbs, although minor limb Our description is based on adult specimens from the scien- reductions can be observed in each genera: in Tre- tific collection of Museu de Zoologia da Universidade de Sa˜o tioscincus, the two phalanges of the first digit are Paulo (MZUSP). We have analyzed two specimens of Psiloph- reduced in size, in Gymnophthalmus and Micrable- thalmus paeminosus Rodrigues, 1991, six specimens of Procello- pharus the distal-most phalanx from the first digit saurinus tetradactylus Rodrigues, 1991, nine specimens of Van- zosaura rubricauda (Boulenger, 1902), six specimens of Notho- is lost, and in Procellosaurinus, Vanzosaura, and bachia ablephara Rodrigues, 1984, two specimens of Psilophthalmus both phalanges of the first digit Scriptosaura catimbau Rodrigues & dos Santos, 2008, and eight are lost. The latter three genera have a snake-like specimens of Calyptommatus nicterus Rodrigues, 1991; refer- body form, with an elongated body and largely ence numbers and sampling sites for each specimen are sum- marized in the Supporting Information. reduced limbs: Nothobachia has a one-digit fore- Specific measurements of all specimens were taken with a limb and a two-digit hindlimb, and Scriptosaura digital caliper to the nearest 0.01 mm: snout-vent length (SVL), and Calyptommatus have no external forelimbs measured from the back of the occipital bone to the posterior and a one-digit hindlimb. end of the pelvic girdle (at the level of the acetabulum); trunk Despite being always recovered as monophyletic, length between pectoral and pelvic limbs, measured from the anterior end of the pectoral girdle to the posterior end of the relationships between Gymnophthalmini genera pelvic girdle; and tail length, measured, in specimens with are still a matter of debate: the phylogenetic hy- intact tails, from the posterior end of the pelvic girdle to the pothesis proposed by Pellegrino et al. (2001) groups end of the tail. the snake-like genera (Calyptommatus and Notho- All specimens were cleared and double stained for cartilage and bone following the methods from Potthoff (1983); Taylor bachia) together, while that proposed by Castoe and van Dyke (1985); Song and Parenti (1995); Springer and et al. (2004) places Calyptommatus as sister group Johnson (2000), and examined with an Olympus SZX12 stereo- to Psilophthalmus, and both to Nothobachia. Scrip- microscope (Olympus, Tokyo). Photographs were taken using an tosaura was only recently described (Rodrigues and Olympus digital camera (DP72) attached to the scope and sche- dos Santos, 2008) and therefore, has not been matic drawings were made using the digital images as shapes. The anatomical terminology follows Romer (1956), Hoffstetter included in any phylogenetic studies so far. and Gasc (1969), Russel and Bauer (2008), and Jerez and Tara- Here, we present a comparative description of zona (2009). the vertebral and appendicular skeletons of six gymnophthalmini species (Procellosaurinus tetra- dactylus, Vanzosaura rubricauda, Psilophthalmus RESULTS paeminosus, Nothobachia ablephara, Scriptosaura Vertebral Skeleton catimbau, and Calyptommatus nicterus; Fig. 1), and discuss the morphological adaptations shown The relative proportion of trunk and tail lengths by both lizard-like and snake-like species that may differs in lizard-like and snake-like species. In Psi- be related to each species’ lifestyle. lophthalmus paeminosus, Procellosaurinus tetra- Journal of Morphology POST-CRANIAL SKELETON OF GYMNOPHTHALMIDS 847 between these two morphotypes; therefore, the fol- lowing description applies to all species and differ- ences, when present, are emphasized. The atlas is the first trunk vertebra. It is com- posed of a small ventral intercentrum and a pair of neural arches that are not fused dorsally (Fig. 2A). Its centrum is incorporated into the centrum of the axis as the odontoid process (Fig. 2A), and does not contact the atlas’s neural arches; the lat- eral extremities of the intercentrum contact the antero-ventral surface of the odontoid process pos- teriorly. The vertebral column connects to the occi- pital condyle in the skull