The Dire Wolf was the largest canine predator of the late Pleistocene epoch in North and South America. Its prey was the megaherbivores. These included peccaries, horses, llamas, bisons, tapirs, sloths, and glyptodonts. Their most common prey is thought to be the horse. The species lived in a variety of environments, from forested mountains to open grasslands and plains ranging in elevation from sea level to 7400 feet. Canis dirus became extinct near the end of the Pleistocene Epoch when their usual prey disappeared.

The Dire Wolf was stockier and had shorter limbs than Gray wolves but were 25% heavier than the smaller species. The Dire Wolf had a wider and taller skull with a great sagittal crest. There is a thickening of the mandible below the carnassial teeth which are larger and more massive than a Gray Wolf. The powerful jaw muscles enabled the Dire Wolf to become a very efficient killer. Dire Wolves lived from 11,000 years ago to 500,000 years ago and shared the landscape with Gray Wolves. It is unlikely they hunted the same prey and this is one of the possible reasons the Dire Wolf died out and the Gray Wolf did not.

The word dirus is Latin for fearful. The Dire wolf is believed to have hunted in packs much as Gray Wolves do today. Hunting in packs allows preditors to kill larger prey and to protect the bodies from larger predators. There was no dimorphism in Dire Wolves and it is surmised that they were monogamous, but we cannot know this for sure. No specimens of puppies have been found.