A megalodon is an extinct species of mackerel shark that lived approximately 23 to 3.6 million years ago, from the Early Miocene to the Pliocene epochs. It was a massive shark, with estimates suggesting it grew to between 15 and 18 meters in length, three times longer than the largest recorded great white shark. Megalodon was a member of the extinct family Otodontidae, which diverged from the great white shark during the Early Cretaceous. Its jaws could open wide enough to swallow two adults standing side by side, and it used its sharp, banana-size teeth to prey on whales, dolphins, seals, and probably other sharks. Megalodon teeth are similar to those of modern white sharks in that they are triangular, serrated, and symmetrical. Infant megalodons were around 3.5 meters at their smallest, and the pups were vulnerable to predation by other shark species, such as the great hammerhead shark and the snaggletooth shark. Megalodon is thought to have managed its body temperature in a manner similar to that of modern white sharks, in that it was not exclusively cold-blooded like most fish.

In summary, a megalodon is an extinct species of shark that lived millions of years ago and was much larger than the great white shark. It had massive jaws and sharp teeth, and it preyed on whales, dolphins, seals, and other sharks.