Primitive Ichthyosaurs existed as early as the Triassic period but their zenith was the Jurassic when there were many different types; some were small and some were giants, and they lived in the deep oceans as well as the shallow seas. They breathed air and had to come to the surface regularly to breathe. They also gave birth to live young; a time when they were very vulnerable to predators such as sharks and pliosaurs like Lipleurodon. Ichthyosaurs were still present in the early Cretaceous but had become extinct by the end of it.

The teeth of an Ichthyosaur lined the length of its long, strong jaws and were blunt to suit a diet of  fish and molluscs, including cephalopods like ammonites.

An Ichthyosaur's eyes were big suggesting that they spent time in the dark depths of the oceans possibly hunting giant squid, much the same as a modern sperm whale does.

Ichthyosaur fossils have been found mainly in modern day North America, South America and Europe, some specimens have also been found in Australia.