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 Boar
Dire Lion
Dire Rat
Dire Shark
Dire Tiger
Dire Weasel
Dire Wolf
Dire Wolverine