Meeting Abstract
Over 30 tetrapod lineages have evolutionarily lost their limbs. Studies of limb and digit loss have revealed a close relationship between the reduction of the appendages and body elongation; however, the reduction and loss of internal structures like the pectoral girdle have been less thoroughly examined. Here, we use computed tomography to examine pectoral girdle morphologies in the skink genus Lerista, which contains pentadactyl and limbless members, as well as transitional morphologies. Our 3D geometric morphometric analysis demonstrates that the loss of the pectoral girdle occurs gradually and in a series of steps loosely associated with the extent of forelimb reduction. The girdle as a whole shows more pronounced reduction anteroposteriorly than mediolaterally, occuring in fairly close association with limb reduction. Certain events occur concurrently such as the loss of the coracoid foramen, which occurs in association with the loss of the humerus. However other events, such as the loss of the epicoracoid, are not consistently associated with any state of limb reduction. Patterns of reduction are clade dependent, with individuals from closely related groups showing dramatically different degrees of girdle reduction despite a similarity in limb state. Despite these differences, the patterns of girdle reduction in Lerista are more similar to each other than to those of other skinks, and are more similar to other skinks than to other squamate groups. Though some aspects of this transition are common to all squamate lineages that have evolved limblessness, this study reveals that even in closely related clades within the same genus, the evolution of limblessness does not proceed in an entirely deterministic way.
