Ichthyosaur

Ichthyosaurs (Ancient Greek for "fish lizard" - ιχθυς/ichthys meaning "fish" and σαυρος/sauros meaning "lizard") were giant marine reptiles that resembled fish and dolphins. Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 245 million years ago (mya) and disappeared about 90 million years ago, about 25 million years before the dinosaurs became extinct.

Jurassic Park
Ichthyosaur has never appeared or metioned in any jurassic park films or books, it has however appeaerd in a few games such as Jurassic Park III: Park Builder.