Some Morphofunctional Features of the Tail of Early Archosaurs Related to Swimming Adaptations

Abstract

Abstract: Fossil and extant aquatic and semi-aquatic tetrapods present several types of structure of the locomotor apparatus, each associated with a particular style of swimming. In the course of the evolutionary adaptation to swimming, morphological transformations of the tail, often the principal means of propulsion, played an important role. Modern reptiles (except turtles) swim mainly using horizontal tail undulation, while mammals use either vertical or horizontal undulation. Among extinct reptiles, sauropterygians probably used vertical tail mobility when swimming. In most archosauromorphs, the tail became high, laterally compressed, and they swam mainly using horizontal movements of the tail. Among early archosaurs, proterochampsians and doswelliids are distinguished by their wide and dorsoventrally flat tails, which may indicate an adaptation to a swimming style that used the vertical mobility of the tail.