The Problem of Polydactyly in Amphibians

E. I. Vorobyeva


In this paper the origin of polydactylous limbs in oldest tetrapods and the digit homology are discussed using new developmental data. These data are obtained in the study of recent hynobiids as one of the primitive families of Caudata. We analyzed the pattern of limb development and morphology in Salamandrella keyserlingii and Ranodon sibiricus in comparison with limb skeleton of ancient tetrapods and their fish ancestors. Special attention is paid to the phenomenon of sixth toes in the development of Ranodon specimen, which is comparable with additional preaxial digits in some Devonian tetrapods such as Ichthyostega, Acanthostega, and Tulerpeton. This phenomenon can be considered as a variant of development connected with the more complete realization of the morphogenetic program common to recent caudates and Palaeozoic tetrapods. A hypothesis regarding the independence of preaxial and postaxial digital arches in oldest tetrapods is proposed.


Caudata; Hynobiidae; polydactyly; evolution; development

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