The reptilian lineages (like plesiosaurs, ichthyosaurs, mosasaurs, thalattosaurs, and others) have become sea creatures. Most of these marine reptiles, often wrongly called "dinosaurs", are extinct. This illustrated book is devoted to these extinct groups of marine reptiles. It also documents research on extinct marine reptiles.

Vertebrae evolution has led to the convergent appearance of many groups of originally terrestrial animals that now live in the seas. There are reptilian lineages that have become sea creatures. Most of these marine reptiles are extinct. This edited book is devoted to these extinct groups of marine reptiles.