North America’s “top dog” traveled a lonely evolutionary path
Dire wolves (red) fight off gray wolves for dibs on a bison kill in this artist’s reconstruction.Mauricio Antón
One of North America’s most famous ancient predators—and a favorite of Game of Thrones fans—emerged as mysteriously as it disappeared. Dire wolves, which died out with mammoths and saber-toothed cats at the end of the last ice age, were long thought to be close cousins of gray wolves. Now, the first analysis of dire wolf DNA finds they instead traveled a lonely evolutionary path: They are so different from other wolves, coyotes, and dogs that they don’t belong in the genus that includes these animals. Instead, researchers argue, they need an entirely new scientific classification.
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“It’s a fascinating study” that reveals just how distinct dire wolves were, says Robert Dundas, a vertebrate paleontologist and expert on the animals at California State University, Fresno, who was not involved with the work.
Archaeologists know dire wolves lived in North America from about 250,000 to 13,000 years ago. They were about 20% bigger than today’s gray wolves—the size of their skeletons often gives them away—and, like other wolves, they probably traveled in packs, hunting down bison, ancient horses, and perhaps even small mammoths and mastodons. Many followed their prey into the sticky asphalt of what are now Los Angeles’s La Brea Tar Pits, where they were trapped for the ages. Hundreds of dire wolf skulls line the walls of the California museum.
But that’s where most knowledge stops. Because the skeletons of dire wolves are similar to those of gray wolves, the two animals were considered closely related. Scientists have long classified dire wolves as Canis dirus, putting them in the same genus as gray wolves, coyotes, and dogs. But the one thing that could have sealed the deal—dire wolf DNA—had been broken down by the tar of the pits.
In the new study, researchers scoured North America trying to extract genetic samples from dozens of dire wolf remains at universities and museums. They recovered about one-quarter of the nuclear genome and the full mitochondrial DNA across five individuals, ranging in age from about 13,000 to more than 50,000 years old.
The genetic material revealed a new evolutionary family tree, and a surprise: Dire wolves occupy their own lineage, separate from those that gave rise to African jackals, gray wolves, coyotes, and dogs by nearly 6 million years, the team reports today in Nature. “Even though they look like wolves, dire wolves actually have nothing to do with wolves,” says Angela Perri, a zooarchaeologist at Durham University and one of the study’s lead authors.
Perri and her colleagues also recovered proteins from the collagen of a La Brea dire wolf, which supported the split between the species. The mounting evidence has convinced the team to recommend taking dire wolves out of the Canis genus entirely and putting them elsewhere in the larger Canid family, which—in addition to wolves and coyotes—includes foxes, jackals, and other doglike carnivores. Dire wolves would become Aenocyon dirus, a designation proposed in 1918, but that scientists largely disregarded.
“The Aenocyon genus was left in the historical dust bin, but it can be resurrected,” says Xiaoming Wang, a vertebrate paleontologist and expert on ancient canids at the Natural History Museum of Los Angeles County. “Based on the genetic data this team presents, I would support that reclassification.”
That could also mean a reimagining of what dire wolves looked like. Artists—and Game of Thrones creators—have often depicted the predators as large timber wolves: bulky, gray, and ferocious. But Perri says living in the warmer latitudes of North America may have given them traits more common to canids and other animals in these climates, such as red fur, a bushy tail, and more rounded ears. As such, she says, dire wolves may have resembled “a giant, reddish coyote.”
Genetic analysis further revealed the predators probably evolved in the Americas, where they were the only wolflike species for hundreds of thousands—or perhaps millions—of years. When gray wolves and coyotes arrived from Eurasia, likely about 20,000 years ago, dire wolves were apparently unable to breed with them, as the researchers found no traces of genetic mixing. That’s unusual, Perri says, as even species as diverse as dogs and coyotes can produce offspring. This further suggests, she says, that dire wolves were a very different animal than these other creatures.
Still, Wang notes the team was unable to get complete genomes from any of its specimens. That could mean there are missing genetic signatures, which could indicate that dire wolves did breed with these other animals, and could further help classify the species. “We’re gaining lots of new insight into the relationship between dire wolves and other canids,” he says, “but there are still open questions.”
As to why the wolves disappeared, scientists only know that they vanished along with other big ice age creatures. Perri suspects climate change may have killed off the large prey dire wolves depended on, and that gray wolves and coyotes survived because they could stalk smaller animals. Human hunting of dire wolf prey may have also played a role, as it’s likely the wolves occupied North America with early Native Americans for thousands of years.
“These animals were not mythological beasts,” Perri says. “They lived among us. Not that long ago, the world was full of creatures we will never see again.”
