| Named By: | H. G. Bronn in 1841 |
| Time Period: | 183-176 Ma Toarcian |
| Location: | France. England - Alum Shale Formation, Beacon Limstone Formation. Germany - Posidonia Shale Formation. Italy - Calcare di Sogno Formation |
| Size: | Up to about 3 meters long |
| Diet: | Piscivore |
| Fossil(s): | Several individuals in varying states of completeness. At least one juvenile is known. Osteoderms are also known |
| Classification: | | Chordata | Reptilia | Archosauromorpha | Crocodylomorpha | Thalattosuchia | Teleosauridae | |
| Also known as: | | Mosellaesaurus | |
Pelagosaurus (meaning "lizard of the open sea") is an extinct genus of thalattosuchian crocodyliform that lived during the Toarcian stage of the Lower Jurassic, around 183 Ma to 175 Ma (million years ago), in shallow epicontinental seas that covered much of what is now Western Europe. The systematic taxonomy of Pelagosaurus has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within Teleosauridae were disputed. Pelagosaurus measured 3 m (10 ft) in length with a weight of 450 kg (1000 lbs), and was markedly similar to the modern-day gharial, which has similar adaptions and carnivorous feeding habits.