megalodon

As an adjective Pleistocene

is of a geologic epoch within the Neogene period from about 1.7 million to 11,000 years ago; marked by the evolution of man, and the extinction of the large mammals.

As a proper noun Pleistocene

is the Pleistocene epoch.

As a noun megalodon is

any of a group of extinct sharks from the Oligocene to Pleistocene epochs.

As a proper noun oligocene

is oligocene period.

As a noun megalodon is

any of a group of extinct sharks from the oligocene to pleistocene epochs.

As an adjective extinct

is (dated) extinguished, no longer alight (of fire, candles etc).

As a noun megalodon is

any of a group of extinct sharks from the oligocene to pleistocene epochs.