Zoological Institute, Russian Academy of Science, Universitetskaya nab. 1, St.Petersburg 199164, Russia

Abstract

Progressive development of horizontal agility between scapulocoracoid and sternum with rotation of scapulocoracoid round vertical axe is a character of Diapsida and Urodela. Sinapsida had the vertical agility in scapulo-sternum articulation that allow all elements of a fore girdle to rotate together round perpendicular axe. Their V-shaped girdle consisted of joint scapula, metacoracoid and protocoracoid on one side and clavicle and interclavicle on the other side. The agility of the blocks was limited by some mussels fixed on them. Triass Mammalia had pectoral girdle similar to cynodontes and monotremes. The adaptation to the jumping led to the necessity to amortize the pushes by arms in many evolution lines of mammals. The junction of the arms and almost immovable pectoral girdle fixed on sternum transferred the efforts to the body. The adaptation to the jumping led to the destruction of direct connection between scapulocoracoid and sternum. The vertical agility of pectoral girdle allowed to locate the long axe of a scapula toward the arms stretched ahead before landing that helped to amortize the pushes. In three groups of ancient mammals: Triconodonta, Multituberculata and Pantotheria metacoracoid evaluate to a small process of scapula. As a result, the body fixed between arms with m.serratus ventralis, that was important for push amortization. The independent character of these changes was proved by junction of clavicle and sternum via the remains of procoracoid in Theria and interclavicle - in Multituberculata. The changing of the arm position in jumping promoted their location in parasaggital plane. However the origin way of push amortization is connected possibly with pulling out the elbow articulation. The necessity of changing of this way of amortization led to the appearance only in Theria the arms in parasaggital plane.