At Harvard University, in the Romer Hall of Vertebrate Paleontology, sit the remains of a monster……Kronosaurus!
Kronosaurus was a 36-foot long prehistoric marine reptile that lived 100 million years ago. Sailing the Cretaceous seas, this was one of the largest and deadliest marine reptiles of all time.
But like many of the other dinosaurs, Kronosaurus died out and became extinct. But the seas are vast and still largely unexplored, so who knows? People thought Coelacanths were extinct too until they started finding them in 1938.
Kronosaurus skeleton @ Harvard