Tylosaurus

Tylosaurus was an Upper Cretaceous mosasaur. It was a large, predatory marine lizard closely related to modern monitor lizards and to snakes. 
In 1918, Charles H. Sternberg found a "Tylosaurus" with the remains of a plesiosaur in its stomach. The specimen is mounted in the United States National Museum (Smithsonian). The plesiosaur remains are stored in the collections. 
Although these important specimens were briefly reported by C.H. Sternberg in 1922, the information was lost to science until 2001. The specimen was rediscovered and described by Everhart. It is the basis for the story line in the new (2007) National Geographic IMAX movie - "Sea Monsters".