Stenopterygius, a very fast swimmer, hunted fish and cephalopods (such as squid). It could be up to four metres long.

This genus was perfectly adapted to life in water and closely resembled modern dolphins. It even had a dorsal fin.

Ichthyosaurs evolved from terrestrial reptiles. The front and back limbs developed into fins and the tail into a powerful tail fin. Ichthyosaurs of the Jurassic period were viviparous (gave birth to live young) rather than laying eggs on land like present-day marine turtles, for example.