Melnyk O. Pectoral girdle biomorphology of vertebrates

Thesis, based on extensive comparative anatomical studies of pectoral girdle of vertebrates, states that the principles and features of the skeleton construction, its internal structure and differentiation of vertebrate pectoral girdle muscles depend on biomorphological adaptations, notably the type and speed movement in the habitat. We base interpretation of causes of skeletal structures origin and muscle differentiation of pectoral girdle in a variety of vertebrates. A new study has confirmed the fin fold theory (Rabl, 1901) and refutes the theory of transformation of paired fin position throughout fish evolution (Harris, 1937). Clavicles in vertebrates prowed to have a various origin and are homologous rather than analogue structures in Anamnia and Amniota; geometry shape of pectoral girdle elements of vertebrates rides on the direction of muscle location and strength of tension during either, one or another function; evolution of coracoid process in mammals associated only with the degree of coracoid pectoral muscle development when being neither analog nor homologue of Anamnia coracoid; functional load on parts of bone with cancellous tissue is greater than on thin compact plate parts; there is no differentiation of dorsal and ventral muscle areas in Selachii and Chondrostei according to lack of pectoral fin movement, while Teleostei (bony fishes) and other species of Amniota have distinct differentiation of these areas into individual muscles because of not only abduction or adduction movement but also with the purpose of undulating body maintenance and all types of manipulate functions. In our hypothesis Tetrapoda pectoral girdle supposed to have aponeurotic progenitor transformed into cartilage and bony structures under the condition of functional load, and not the reverse. We found that most Tetrapoda species posses developed extensor of shoulder and elbow joints. The development of certain muscles or certain muscle groups associated only with exposure to functional loads, which in turn related to biomorphological adaptation to different types of support, locomotion and variety manipulation action of pectoral limb.