Body elongation and limb reduction in the genusChalcidesLaurenti 1768 (Squamata Scincidae): a comparative study

Abstract

The present paper analyses the postcranial skeleton and limb reduction in some species of the genus Chalcides Laurenti 1768. Three morphotypes are identified, related to as many adaptive zones.The first type includes the most primitive species, pentadactyls, which PASTEUR (1981) placed in two groups: Chalcides ocellatus and C. thierryi. The most primitive phalange formula is found in species of the C. ocellatus group (2-3-4-4-3/2-3-4-5-3): it differs from the plesiomorphic condition of the Squamata (2-3-4-5-3/2-3-4-5-4) due to the loss of a phalange in the fourth digit of the forelimb and fifth digit of the hindlimb. The mean number of presacral vertebrae (PV) varies from 34.8 in C. sexlineatus to 40.9 in C. ragazzii bottegi (37.1 in C. viridanus, 38.3 in C. colosii, 38.1 in C. polylepis, 38.0 in C. ragazzii ragazzii, 38.5 in C. ocellatus and 39.4 in C. bedriagai). In species of the C. thierryi group, which are more slender than the preceding ones, the mean number of PV is greater (40.8 in C. pulchellus, 43.7 in C. thierryi); the phalange formula is 2-3-4-4-3/2-3-4-5-3 in C. pulchellus and 2-3-4-4-3/2-3-4-4-3 in C. thierryi.Species of the first morphological type generally live in open areas with short thick vegetation, rich in stones and vegetal detritus under which they can hide. Some species are also found in sandy coastal dunes where they show semifossorial habits (such as C. bedriagai), and in pre-desert areas (such as C. ocellatus).The second morphological type includes the psammophile and semifossorial species of the C. mionecton and C. mauritanicus groups. The C. mionecton group is distinguished by a pronounced elongation and narrowing of the body ( 4 7.1 PV in C. mionecton, 50.0 in C. armitagei), a marked limb reduction from pentadactyl (2-3-4-4-3 or 2-3-4-4-2/2-3-4-5-3) to tetradactyl (2-3-4-4-0/2-3-4-5-0) in C. mionecton and to tridactyl in C. armitagei (0-2-3-3-0/0-2-3-4-0), and a generally very small ear opening. The distinctly fossorial species of C. mauritanicus group has an even longer and narrower body (50. 7 PV), greatly reduced limbs didactyl anteriorly and tridactyl posteriorly (0-0-2-3-0 or 0-0-1-3-0/0-2-3-4-0), and a completely obliterated ear opening. Species of this morphological type live mainly in sandy coastal zones.The third morphological type, affiliated with the C. chalcides group, dwells exclusively on surface grassland and is never fossorial. The species of this type show the greatest degree of body elongation and limb reduction, ranging from the western Hypothetically, the tendency toward limblessness and acquisition of a serpentiform habitus in the genus Chalcides has followed two separate paths: one favouring subsurface locomotion in sandy coastal environments (species of the C. mionecton and C. mauritanicus groups), the other favouring locomotion in thick grass vegetation (species of the C. chalcides group).

The cranial osteology and dentition in the scincid lizards of the genusChalcides(Reptilia, Scincidae)

“…A group of small to medium-sized terrestrial lizards with cryptic habits, it includes 28 viviparous species mainly differing in degree of body elongation and limb reduction (Caputo et al, 1995(Caputo et al, , 2000Gréer et al, 1998). They can be placed along a broad, graduated morphocline that goes from lacertiform lizards with pentadactyl fore and back limbs to serpentiform ones with very small limbs bearing a reduced number of fingers and phalanxes, or none at all (Caputo et al, 1995). The latter species tend to use lateral body undulation rather than limb movement for locomotion.…”

How Lizards Turn Into Snakes: A Phylogenetic Analysis of Body-Form Evolution in Anguid Lizards

“…The transition is well studied in that numerous authors have addressed the evolution of snakelike squamates, but is poorly studied in that none have used phylogeny-based comparative methods. Several authors have noted a relationship between increase in vertebral number and decreases in limb size and number of digits or phalanges (e.g., Camp 1923; Stokeley 1947;Presch 1975;Greer 1987;Caputo et al 1995). Gans (1975) discussed morphological, functional, and ecological correlates of limb loss in tetrapods, noting that body elongation, reduced body size, and undulatory locomotion seem to be associated consistently with limb reduction.…”

“…Previous authors have hypothesized relationships between body elongation and reduction in limb size and between reduction in limb size and loss of digits (Gans 1975;Presch 1975;Lande 1978;Caputo et al 1995;Greer et al 1998;Lee 1998), between limb reduction and reduction in overall body size (e.g., Rieppel 1988;Griffith 1990;Lee 1998), and between the evolution of snakelike body form and a burrowing lifestyle (e.g., Gans 1975;Rieppel 1988;Caputo et al 1995;Lee 1998). These hypotheses generally have been formulated by comparing species with different degrees of limb reduction and (implicitly) assuming that the phylogeny tracks a morphocline of increasing limb reduction and that different species represent different stages in a process that is largely uniform among species (e.g., Gans 1975;Lande 1978;Caputo et al 1995;Greer et al 1998). Rigorously testing these hypotheses requires statistical methods that incorporate phylogeny (e.g., Felsenstein 1985a).…”

Role of paraxial mesoderm in limb/flank regionalization of the trunk lateral plate

“…Instead, the number of somites associated with the flank in lizards may contribute to the relative proportions of the limbs to the trunk. Indeed, there is a known correlation between limb reduction and trunk elongation in several lizard lineages (e.g., Wiens and Slingluff, 2001), and small-limbed lizard species with an elongated trunk tend to have more trunk vertebrae (and, therefore, more trunk somites) than their close relatives (e.g., Presch, 1975;Greer, 1987;Caputo et al, 1995).…”