This is a very nice, beautifully preserved complete fossil specimen of an extinct giant shark! It even still has serrations.
Megalodon (Carcharocles megalodon), meaning "big tooth", is an extinctspecies of shark that lived approximately 23 to 2.6 million years ago (mya), during the Early Miocene to the end of the Pliocene. It was formerly thought to belong to the family Lamnidae, making it closely related to the great white shark (Carcharodon carcharias). However presently there is near unanimous consensus that it belongs to the extinct family Otodontidae, which diverged from the ancestry of the great white shark during the Early Cretaceous. Its genus placement is still debated, authors placing it in either Carcharocles, Megaselachus, Otodus, or Procarcharodon.