Direwolfs are one of the most famous prehistoric carnivores in North America. Along with there extinct competitor(s): smilodon, scimitar and mountain lion. Terrible scary wolf dogs lived in the Americas and eastern Asia during the late pleistocene and early holocene epochs, 125,000–9,500 years ago.
The species was named in 1858, four years after the first specimen had been found. Two subspecies are recognized: Aenocyon dirus guildayi and Aenocyon dirus dirus. The largest collection of its fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles. Like smilodon (sabre tooth), thousands of specimens were pulled from here.

Biology:
Dire wolf, aenocyon dirus, were hyper carnivores. Ie. they ate greater than a 70 percent meat diet. They were about 5 feet head to tail. 25% larger than the largest dogs (american massif). Males and females were similar sizes however the males had alittle larger teeth to attract mates. There teeth were strong enough to crush bones, so they could eat and digest marrow. They were about the same size as the largest modern gray wolves (Canis lupus), the Yukon wolf and the northwestern wolf.
A. d. guildayi weighed on average 60 kilograms (132 lb) and A. d. dirus was on average 68 kg (150 lb).
Terrible scary wolf dogs skull and dentition matched those of C. lupus (grey wolfs), but its teeth were larger with greater shearing ability. And, its bite force at the canine tooth was stronger than any known Canis species. Its limbs may have also been lighter and more gracile allowing it to quickly chase down prey. These characteristics are thought to be adaptations for preying on late pleistocene megaherbivores, and in North America. Its prey is known to have included western horses, ground sloths, mastodons, ancient bison, camels and more.

Temporal range:
Dire wolf remains have been found across a broad range of habitats including the plains, grasslands, and some forested mountain areas of North America. The arid savanna of south America, and the steppes of eastern Asia. Sites range in elevation from sea level to 7500 feet. There fossils have rarely been found north of 42°N latitude. They have been found Arizona, California, Florida, Idaho, Indiana, Kansas, Kentucky, Missouri, Nebraska, New Mexico, Oregon, Pennsylvania, South Carolina, South Dakota, Texas, Utah, Virginia, West Virginia, Wyoming, and Nevada.
Fossils found at the natural trap cavern in Wyoming with sloth and beringa wolves, may indicate there expansion north of 42 N lattitude. This may have had to do with the division between the Laurentide and the Cordilleran Ice Sheet(s). A temporary channel between them could have existed that allowed a small number of them to follow prey north.
The five unconfirmed reports of dire wolf fossils north of 42°N latitude are at Fossil Lake, Oregon (125,000–10,000 YBP), American Falls Reservoir, Idaho (125,000–75,000 YBP), Salamander Cave, South Dakota (250,000 YBP), and four closely grouped sites in northern Nebraska (250,000 YBP).
Major fossil sites for terrible scary wolf dogs are located east of the Rocky Mountains and include Friesenhahn Cave, near San Antonio, Texas; Carroll Cave, near Richland, Missouri; and Reddick, Florida.
10-15 sites have been Remains have also been found in south America and Mexico. Including San Josecito cave where like La Brae, a great presence of remains were identified.

Did you know?
In 2020, mandibles from a dire wolf was found in the vicinity of Harbin, northeastern China. The fossil was described and dated 40,000 YBP. This discovery challenges previous theories that cold temperatures and ice sheets were a barrier for dire wolves. It is proposed that the dire wolf followed migrating prey across Beringia into Eurasia. The find and hypothesis is still being studied.

Like dogs (others) taxonomy and evolution changed:
From the 1850s, the fossil remains of extinct large wolves were being found in the United States. It was not immediately clear that these all belonged to one species. The first specimen that became associated with aenocyon dirus was found in mid-1854, in the bed of the Ohio River near Evansville, Indiana. Paleontologist Joseph Leidy determined the specimen represented an extinct species of wolf. He reported it under the name of canis primaevus. It was around the 1980s scientist re-attributed the genus and species to aenocyon dirus. Before then, they had a number of synonmyns including: aenocyon dirus nebrascensis, canis ayers, canis dirus, canis indianensis, canis mississippiensis, canis nehringi, canis primaevus and others.

Did you know? There is no evidence Terrible or scary wolf or dog interbred with grey wolf.

Behavior:
Sexual dimorphism, (difference in male and females, other than sex organs), aside from teeth, there was little variance. Indicating that dire wolves lived in monogamous pairs. Their large size and highly carnivorous dentition vindicated direwolfs fed on large prey. To kill megafauna larger than themselves, they needed to rely on more than there strong teeth and jaws. Often consisting a alpha. They were forced to worked together as packs consisting of an mating pair and their offspring from the current and previous years.

A. d. guildayi (the smaller of the direwolfs) is the most common carnivoran found at La Brea. Remains of dire wolves outnumber remains of gray wolves in the tar pits by a ratio of five to one. It is thought, during the Last Glacial Maximum, coastal California, had a climate slightly cooler and wetter than today, and that it was a refuge. Because of this, and the larger numbers of dire wolfs found there. It is likely that fairly sizeable groups fed there together. The many A. d. guildayi remains found in the tar pits also suggests that were social predators.
The large size of the dire wolf provides an estimated prey size in the 300 to 600 kg (660 to 1,320 lb) range.
Analysis of bones and fecal mater show they had a preference for consuming ruminants such as bison. They moved to other prey such as lama, camel, horse and others when food became scarce. They even occasionally scavenged on beached whales along the Pacific coast when available. Example: A pack of modern timber wolves can bring down a 500 kg (1,100 lb) moose as their preferred prey. A pack of dire wolves bringing down a bison thus is conceivable.

Did you know: Predatory birds and mammals were attracted to dead or dying herbivores at La Brae tar pits,that had become bogged. It would then trap the predators.
It is estimated that herbivore entrapment occured once every fifty years. For every instance of herbivore remains. There were ten carnivores.

Tooth breakage:
Tooth breakage relates to carnivore’s behavior.
One study of fossilized remains of large carnivores from La Brea pits dated 36,000–10,000 years ago shows tooth breakage rates of 5–17% for the
dire wolf, coyote, American lion, and smilodon, compared to 0.5–2.7% for ten modern predators. The dire wolf broke its incisors more often
when compared to the modern gray wolf; thus, it has been proposed that the dire wolf used its incisors more closely to the bone when feeding.
A theory exists: When humans arrived, climate was already changing; and, there was a limited prey availability. Competition between carnivores increased, causing them to eat faster and consume more bone, leading to more tooth breakage. As greater prey became extinct around 10,000 years ago, so did the terrible scary wolf dog carnivores, or direwolf.

Competitors:
Before the appearance of the dire wolf, North America was invaded by the genus xenocyon (species of wild dog or canis). They were as large as the dire wolf but more hypercarnivorous. Evidence indicate that these, the dire wolf, smilodon, and the american lion competed for the same prey. Other large carnivores included the north American giant short-faced bear (arctodus simus), cougar (puma concolor), pleistocene coyote (canis latrans), and pleistocene gray wolf. These predators may have also competed with humans who hunted for similar prey.
At the recent find in eastern asia. The dire wolf would have even competed with cave hyena (crocuta crocuta ultima). Competition with this species may have kept Eurasian dire wolf populations very low, leading to the paucity of dire wolf fossil remains in this otherwise well-studied fossil fauna.

Extinction:
During the quaternary extinction event around 12,700 years ago, 90 genera of mammals weighing over 44 kilograms (97 lb) went extinct.
Scientists still debate what contributed to the event. Including overhunting, climate change; a large comet; natural disasters; or what was probably combination of factors .
Carnivores and scavengers definitely contributed to the extinction of the megaherbivore prey upon which they depended. Both dire wolf and beringian wolf went extinct, leaving only the less carnivorous and more gracile wolf to thrive. One study proposes gray wolves and coyotes survived due to their ability to hybridize with other canids. Such as the domestic dog. And, to acquire traits that resist diseases brought by taxa arriving from Eurasia, and elsewhere.
Who would have guessed such a well known critter would create so much information and folklore. Here’s to the terrible scary wolf dog, or direwolf.