The ichthyosaurs are the most frequently and best studied reptiles of the Jurassic. The longest known specimens measured up to 18 metres in length. Their ancestors were saurians living on land.
They repeatedly had to swim to the surface in order to breathe. Their anatomy was so perfectly adapted to life in the water that they could no longer crawl onto the land to lay their eggs but, like mammals, gave birth to fully developed young. They were fast-swimming predators.
In their stomachs one can occasionally find undigested remains of their last meal: tentacles of squid, or the scales and bony remains of fish.