Limb Reduction in the Scincid Lizard Genus Lerista. 2. Variation in the Bone Complements of the Front and Rear Limbs and the Number of Postsacral Vertebrae

Morphoclines for the front and rear limb bone configurations in the sand-swimming lizard genus Lerista trace only a very narrow pathway through morphological space. The morphoclines are generally finely-graded and linear, except for one mutually exclusive pair of osteological configurations in the manus and one in the pes. These alternative states plus the occurrence of adult configurations not seen in the development of generally primitive tetrapods suggest that limb reduction in Lerista is not simply the global truncation of a primitive developmental sequence. A circumstantial argument is made for the functional significance of at least some of the observed morphology: the condition of near or complete absence of the front limb in conjunction with the retention of two toes on the rear limb is common in Lerista and two other skink lineages inhabiting fine, loosely-consolidated sand. The various configurations in the Lerista morphoclines are disproportionately represented by species; this may reflect speciation opportunities in various habitats. Numbers of postsacral vertebrae are not sexually dimorphic. Coefficients of variation of postsacral vertebrae exceed those for presacral vertebrae, reflecting inversely the relative functional importance of the two parts of the vertebral column. In interspecific comparisons, the number of phalanges in the pes is positively correlated with the number of phalanges in the manus and negatively correlated with the numbers of presacral and postsacral vertebrae. Functionally, this reflects the supplementary relationship between the modalities of limbed locomotion (phalanges) and the com- plementary relationship between the modalities of limbed and trunk locomotion (vertebrae). Among tetrapods lizards are renowned for the many lineages that have undergone limb reduction independently, and among lizards,