Peculiarities of the Structure and Locomotor Function of the Tail in Sauropterygia

Abstract

Among ancient and modern marine reptiles, several structural types of the locomotor apparatus were or are present, supporting different styles of swimming. Ichthyosaurs, mosasaurs, saltwater crocodiles, and representatives of many other groups swam or swim with horizontal undulations of the body primarily using the tail with a vertical caudal fin. Sea turtles with a reduced tail and their body completely immobilized by the shell use only limbs transformed into flippers for swimming. Sauropterygians had a substantially immobilized trunk and a horizontal caudal fin. They used a unique type of subaquatic locomotion with the leading role of two pairs of powerful flippers and vertical undulations of the tail, partial analogs of which are found in sea turtles, sirens, cetaceans, and some semi-aquatic mammals.