[Morphogenetic approach to the formation of paired limbs in the course of tetrapodization].

Transition from sarcopterygians to tetrapods is analyzed based on new paleontological, ontogenetic, and molecular data. It is shown that transformation of skeletal fin elements into the tetrapod limb followed the patterns of divergent, parallel, and mosaic development. Morphogenetic plasticity and autonomy of these processes as well as the same developmental bauplan for the limbs of Urodela and Anura are proposed. Variations observed in these processes are regarded as a result of larval adaptations and heterochronies. The latter excludes recapitulation of successive archetypical states (transformation-development of the fish fin into tetrapod limb). The idea that the digits are a novelty relative to the distal radials of the fin is supported.