This is a  big mosasaur tooth in a display box and accompanying information label. While it does have a couple of repairs, as pictured, this does not detract from the enormous size of the tooth measuring 2.59 inches!
 
Despite what has been portrayed in popular movies, Mosasaurs were not dinosaurs, but rather aquatic reptiles more closely related to monitor lizards. The largest is estimated to reach nearly 50 feet, while others were far more modest in size, measuring between 3- 13 feet.