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Journal Article

Evolutionary Mechanisms of Limb Loss in Tetrapods

Russell Lande
Evolution
Vol. 32, No. 1 (Mar., 1978), pp. 73-92
DOI: 10.2307/2407411
Stable URL: http://www.jstor.org/stable/2407411
Page Count: 20

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Topics: Evolution, Lizards, Genetics, Toes, Skull, Genetic mutation, Species, Mammals, Fossils, Limb buds
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Evolutionary Mechanisms of Limb Loss in Tetrapods
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Abstract

A review of fossil evidence on the rates of limb loss in tetrapods indicates that millions of years are required for complete loss of external traces of limbs. Morphological series of intermediate stages of limb loss within genera in the lizard families Scincidae and Teiidae show that there are evolutionary pathways of body elongation and reduction of limb size relative to skull length, accompanied by loss of limb elements beginning distally. Evolutionary elongation of the lizard body occurs through an increase in the coefficient of allometric growth of the body with respect to the skull, which precedes structural reduction of the limbs. A review of embryological studies of limbed and limbless forms suggests that in amniotes the distal to proximal sequence of structural reduction evolves by the progressively earlier onset of cell death which usually occurs to form the spaces between the digits, in conjunction with the normal proximo-distal sequence of determination of mesodermal elements in limb development. Following a presentation of data on digital variation in lizards, genetic studies of digit loss and polydactyly are summarized which indicate a polygenic influence on structural variation. Using these data, mathematical models are constructed which show that weak selection pressures can produce geologically rapid structural changes. The mechanism of reexpression of long lost structures of the limb (such as cetacean pelvic limbs and atavistic digits in the horse, dog, and guinea pig) is considered in a view of information on appendicular mutations in the mouse.

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