Limb Reduction in the Lizard Genus Lerista. 1. Variation in the Number of Phalanges and Presacral Vertebrae

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Abstract
The sandswimming, Australian scincid lizard genus Lerista is the best example of limb reduction in tetrapods in that it comprises an extensive and finely graded morphocline within a group of 51 closely related species. This paper analyzes variation in the number of phalanges and presacral vertebrae within populations and among species. Within populations, phalangeal number varies little and variation is usually symmetrical within individuals. The number of presacral vertebrae is sexually dimorphic, with females averaging 0.4-2.0 more than males. Among species there is a strong, curvilinear, inverse relationship between the number of phalanges and the number of presacral vertebrae. The interspecific morphoclines of phalangeal complements based on the total number of phalanges show that digits in both the manus and pes are lost in the order 1 > 5 > 2 > 3 > 4. Such morphoclines are perfectly linear except at one point in the pes where the series branches to accommodate two mutually exclusive configurations. If these morphoclines represent phylogenetic reductions and if phylogenetic reductions are hypothesized to be globally arrested stages of a basic developmental pattern, then one of these pes configurations must constitute an exception to this generation. At least one other observed configuration is also likely to be outside a basic, global ontogenetic sequence for the genus.