Dire Animal
Dire animals are normal animals on steroids. They're vaguely based off of animals from the Late Pleistocene and Early Holocene epochs.
They were introduced in 3.5, presumably as a way to add some higher level animals to help make the abilities of druids and rangers matter.
The following were introduced in the first Monster Manual, but there was a shitton of them added on in virtually ever book.
Dire Ape
Dire Badger
Dire Bat
Dire Bear - Dire bears are savage hunters that can eat humanoids as readily as game animals.
Dire Boar
Dire Lion
Dire Rat
Dire Shark
Dire Tiger
Dire Weasel
Dire Wolf
Dire Wolverine