For over 150 years, the Dire Wolf, originally known as Canis dirus and now classed as Aenocyon dirus, was believed to be a specialized version of the ordinary North American Gray Wolf, Canis lupus, that was slightly bigger and had a heavier skull to tackle larger Ice Age prey. But in 2020, an examination of DNA extracted from Dire Wolf skeletons changed that picture entirely.
Dire Wolf skulls on exhibit at the LaBrea Tarpits in Los Angeles
The Dire Wolf has been one of the most common fossils to be found in North American Ice Age deposits. Since the first find—a lower jawbone—was uncovered in 1854 in Indiana, there have been tens of thousands of additional discoveries, ranging from California to Florida. At the LaBrea Tarpits in Los Angeles, Dire Wolves are by far the most common fossils, with some 3,600 bones, skulls, or complete skeletons being dug out of the tar at this location alone. The species has been found in both North and South America, dating from the last Ice Ace, which ended almost 10,000 years ago. At first, several of these specimens were described as separate species, but by 1915 it was recognized that they were all the same, and were combined into the species Canis dirus, with two recognized subspecies being named in 1984 (the eastern subspecies had slightly longer legs and bigger teeth). Some “splitter” taxonomists, moreover, had always considered the Dire Wolves to be different in some minor ways from the ordinary wolves and had proposed a new genus for them, Aenocyon, but this was not widely accepted.
Examinations of the skeletons indicated that the Dire Wolf was very similar to today’s Gray Wolf which had itself evolved from an ancestor in Europe that had migrated across Asia and entered North America through the Beringia land bridge about one million years ago, adapting along the way into the Canis lupus species. The Dire Wolf, it was presumed, was a close relative which had become specialized as a pack hunter to take down larger Ice Age prey like Mammoths and Giant Bison. It was found in a variety of habitats throughout its range, from forested mountainsides to open grasslands.
In the 2010s, Dr Angela Perri began a project to study the Dire Wolf by attempting to extract and sequence its DNA. Since there are many thousands of Dire Wolf bones that are both relatively recent and quite well-preserved, she assumed this would be an easy task. It was not. Most of the best-preserved bones came from LaBrea, and it was found that the petroleum tar deposits had permeated all the bones and destroyed the DNA. That was a dead end. By this time, Perri’s team had joined forces with a number of others (49 scientists in all, including Australian geneticist Dr Kieran Mitchell and other researchers from England and Germany) who had been working on the same goal, and together they systematically scoured the vast collection of bones to find intact genes. Only five bones were suitable, dating from 50,000 to 13,000 years ago. From this, geneticists were able to extract and sequence all of the mitochondrial DNA and about 25% of the nuclear DNA.
When the team compared the Dire Wolf DNA to that of living canines like Gray Wolves, Coyotes and Dholes, however, they got a shock. There were significant differences in the genes, indicating that the Dire Wolf and the Gray Wolf lineages, far from being recent close cousins, had been evolving separately from each other for a very long time. They were not even close enough to be in the same genus, and Perri’s team resurrected the genus name Aenocyon (“terrible wolf”) for the Dire Wolf.
The discovery upended everything that paleontologists assumed about the canids. It had always been thought that as a close relative of the extinct Dire Wolf, the still-living Gray Wolf could serve as a model to help understand the social behavior and even the appearance of the Ice Age creatures. But now all that went out the window. Instead, the Dire Wolf’s closest living genetic relatives seem to be the Side-Striped Jackal and Black-Backed Jackal of South Africa—and those are pretty distant relatives. Their lines had split millions of years ago, when the ancient ancestors of the Dire Wolf left Africa, crossed Asia, and followed the Beringia land bridge into North America.
So we now know nothing at all of the Dire Wolf’s social behavior. Did it live in packs like wolves, or was it mostly solitary like Coyotes? We don’t know for sure. What still seems certain, however, is that the robust skull and jaws are suited for taking down large prey, and the multitude of individuals found at certain sites indicates that it probably was a pack hunter. It likely was driven to extinction at the end of the Ice Age when the megafauna on which it depended died out from the changing climatic conditions.
The less-specialized Gray Wolves, which could adapt to a wider variety of smaller prey, made it through. The Dire Wolves, however, have no living descendants, and their ancient line died out. The two canines were only distantly related, and a comparison of the two genomes does not show any indication that they ever interbred and shared genes, despite sharing their range for tens of thousands of years. Further, since American wolves are able to hybridize with African jackals and Eurasian domestic dogs, this indicates that the Dire Wolf lineage extends back to before even the distant common ancestor of these different Old World species. The Dire Wolf may have been evolving independently for perhaps as long as six million years before the ancestors of the Gray Wolf and Coyote ever arrived in the western hemisphere.
In 2017, moreover, a jawbone identified as a Dire Wolf was found in northeastern China. This indicates that unlike the Gray Wolf lineage, which evolved in Asia and crossed the Bering land bridge to North America, the Dire Wolf evolved in North America and may then have been able to cross back to Asia in the late Ice Age. But it was apparently unable to thrive there, perhaps due to better-adapted competitors from the Canis genus, and remained rare before dying out.
There were also Paleo-Indians in North America at the end of the Ice Age, who shared habitat with the last of the Dire Wolves. But we know nothing of what interactions there might have been between them. Genetic studies on bones have indicated that while the early Paleo-Indians possessed domesticated dogs that lived with them, these were not descended from the North American Gray Wolf populations, but had already been domesticated from Eurasian wolves and were brought along by the humans when they crossed the land bridge into Alaska. There is so far no evidence that Dire Wolves were ever domesticated by humans.