The operational approach to the problem of tetrapodization

The problem of tetrapodization is considered as a part of the general problem of the formation of large higher taxa on the basis of morphophysiological and morphogenetic organization of ancestors. It is shown that the formation of tetrapod-like characters in Paleozoic crossopterygians followed the patterns of preadaptation, parallel and mosaic development. The main task of the operational approach to the problem is the reconstruction of the sequence and rates of the formation of tetrapod-like characters in crossopterygians, the loss of fish characters at the tetrapod level, and the mechanisms of these processes.