Mesosaur Tooth, 100 Million Years Old
Fossil Tooth from a Mesosaur, with seven large & three small teeth, set into a rock matrix with bone jawline.
Liodon anceps species, Cretaceous period, around 100 Million Years Old.
For a re-creation of the beast, have a look at this Discovery Channel re-creation.
The Mosasaur was a large marine reptile, air breathing & used its tail for propulsion. They probably relied on ambush predation, much like a crocodile, and they are known to have eaten ammonites - the shells of which sometimes show the distinct line of a Mosasaur's teeth puncturing through as the result of a savage bite. They were the dominant predator of the Cretacious seas.