The Megalodon Shark became extinct at the end of the Pliocene Era, 1.5 million years ago. Sharks will go through about 20 thousand teeth in its lifetime. This tooth is among the largest found and came from a 50 foot Megalodon that lived about 20 million years ago. By comparison, the largest Great White Shark recorded is under 20 feet, with the largest tooth being under 3 inches
The picture here is a drawing of what the meg may have looked like while alive.