Plesiosaurs in general are thought to be among the slowest marine reptiles. Their long necks are assumed to have created a lot of resistance reducing their hydrodynamic characteristics. For example, the long neck of Elasmosaurs (another type of Plesiosaur) would have made them very slow. Their necks were nearly twice as long as their body. It is believed that Plesiosaurs did not rely on speed to chase down prey, but instead probably ambushed prey from below, coiling and striking their long necks quickly like a snake. In this way they could sneak up on prey by lurking in the darkness of deeper water, and then strike upwards quickly to take prey by surprise (Everhart, 1998).
Above illustration Cryptoclidus: a long necked plesiosaur from a reconstruction based on the work of Dr. David Brown as published in The Illustrated Encyclopedia of Dinosaurs, Salamander Books LTD, 1985.

Table of Contents

What is a Plesiosaur

Types of Plesiosaurs