A NEW APPROACH TO THE PROBLEM OF TETRAPOD ORIGIN

Abstract

The historical and methodological aspects of the problem of tetrapod origin are discussed. Its importance in the development of the evolutionary morphological investigations is emphasized. At present, in addition to new paleontological discoveries, the comparative and experimental researches of the developmental processes (ontogeny), determined by the idea of the morphogenetic community of all sarcopterygians, including crossopterygians, dipnoans, and lower tetrapods, are brought to the foreground. The differences between species demonstrate the evolutionary diversity in their developmental programs displayed in the definitive morphology. The heterochronies of development, including paedomorphosis, and playing an important role in the evolutionary morphological transformations of the crossopterygians and dipnoans and in the formation of the tetrapod organization, are indicated as a phenomenon, whose mechanisms are presumably genetic, cell-tissue, and hormonal. These mechanisms probably include mainly the displacement of the gene manifestation in time at early ontogenetic stages.