Dire Animal

A whole Menagerie of Dire Animals. Looks like bone spikes are all the rage these days.

"They're like wolves but they're dire"

– South Park , Stick of Truth

Dire Animals are a term introduced in Dungeons & Dragons 3rd Edition, but the concept is far older than that, with countless Giant Man-eating [insert animal here] monsters appearing in BX/BECMI. The basic idea is that Dire Animals represent an "uber form" of a given animal - an animal that isn't so much magical as just insanely huge and badass beyond the limits of its normal kinsfolk. Like, you remember the wave of giant killer animal movies kickstarted by Jaws? Or the "giant prehistoric animals" common of Sword & Sorcery? That's basically what Dire Animals are in a nutshell.

Plus it doesn't hurt that they give druids and rangers the ability to stay relevant at higher levels, when "command a brown bear" just doesn't cut it anymore, because you're fighting things like dragonspawn on a regular basis.

Dire animals in 3e are typically portrayed as bigger and "more primal", which usually tends to boil down "stick lots of bony spikes on it and exaggerate the fangs/claws/teeth/horns". They have sometimes been suggested as a stand-in for primeval megafauna - the beasties of the Late Pleistocene and Early Holocene epochs - which used to appear alongside dinosaurs in Advanced Dungeons & Dragons, but other books have explicitly statted various examples of such megafauna as completely separate entities from the Dire Animal template. (For some reason, an actual template was never made for Dire animals.)

For what it's worth, in the Monster Manual #1, the Dire Animal template's entire fluff boils down to this: Dire animals are larger, tougher, meaner versions of ordinary animals. Each kind tends to have a feral, prehistoric, or even demonic appearance.

The Dire Wolf, the one who started this whole mess, is actually based on a real life prehistoric wolf species, Aenocyon dirus. Real dire wolves weren't much bigger than modern day Canis lupus, but they had bigger teeth and a much stronger bite.