A functional morphological study of limb regression in some Southern African species of Scincidae (Reptilia : Sauria)

Doctoral Thesis


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University of Cape Town

How and why did limblessness evolve in certain skinks? These questions are explored in certain species of the Scincidae (from southern Africa) that vary in the degree of limb reduction. This regression series consists of Mabuya capensis (with normal, pentadactyle limbs), Riopa sundevallii (with miniaturized, pentadactyle limbs), three species of the genus Scelotes (bipes, gronovii and brevipes - with vestigial hindlimbs varying in the degree of degeneration) and, finally, Acontias meleagris(without any trace of limbs). The osteology and the myology of the locomotor apparatus are described for all members of this regression series with special reference to the axial system which has in the past received but scant attention compared with the appendicular apparatus. Qualitative and morphometric data are used to construct morphoclines that are correlated with limb reduction. Numerous morphological trends and tendencies support the conclusion that the axial system hypertrophies as the appendages degenerate. The patterns of locomotion are also described for all members of the regression series. Furthermore, an ethocline, that links the limbed and limbless extremes, is postulated. Even in quadrupedal skinks the dominant appendicular system may be assisted by axial flexures that increase stride length. As limbs degenerate, appendicular progression is phased out while axial progression increases in importance.

Bibliography: leaves 342-359.