Thanks to Brilliant for supporting this episode
of SciShow. Go to Brilliant.org/SciShow to learn how to
level up your STEM skills. [♩INTRO] When you hear the words dire wolf, your mind
might jump to Game of Thrones… or Dungeons and Dragons. But dire wolves are not just in the realm
of fantasy and fiction, they were real animals that lived during the last Ice Age. Paleontologists have found thousands of dire
wolf fossils at over one hundred fossil sites, but there’s still a lot we don’t know
about them, and we’re still finding new surprises. For instance, a study published in 2021 found
that dire wolves… aren’t wolves. We know from the fossil record that dire wolves
roamed North and South America between 250,000 and 13,000 years ago, during the Late Pleistocene
Epoch. Or, as we sometimes call it, the Ice Age. They were some of the most common predators
of the Ice Age. More than 4,000 dire wolf specimens are known
from a single site -- the La Brea Tar Pits in California. Overall, dire wolves are very similar to gray
wolves, but with a few key differences: they’re slightly larger at around 70 kilograms, and
they have bigger and stronger jaws and teeth. This beefier build might have helped them
to hunt larger prey, or to crack more bones to get at the nutrients inside. But aside from those few differences, dire
wolves and gray wolves are so similar that their fossil skeletons can be tough to tell
apart. That, plus the fact that both species lived
alongside each other in the past, has led paleontologists to infer that they’re close
relatives. For a long time, dire wolves have been classified
under the scientific name Canis dirus, in the same genus as gray wolves -- Canis lupus. But the 2021 study really throws a wrench
in that idea, with help from ancient DNA. Fossil bones and teeth are great for learning
about ancient animals’ lifestyles and relationships with other species, but they don’t always
tell the whole story. Ancient DNA can provide clues that are missing
in an animal’s anatomy, and it can be especially useful when trying to understand ancestry. Now, dire wolf fossils are common, but ancient
DNA is rare, so the researchers had to cast a wide net. They ended up finding well-preserved DNA in
five dire wolf fossils from all across the U.S., and they managed to sample both the
nuclear genome and the mitochondrial genome. The mitochondrial genome complements the main
genome housed in the cell’s nucleus. Together, they can give us a fuller picture. When they compared this DNA to living canines,
they were surprised to find that dire wolves and gray wolves weren’t closely related
at all. Now dire wolves are still, of course, canines
-- it’s not like they’re bears or something. But based on this genetic comparison, dire
wolf and gray wolf ancestors diverged around 5.7 million years ago. That’s earlier than many other canines,
like coyotes, African wolves, African wild dogs, and jackals. An earlier split means a less recent common
ancestor. Which means that all those guys—coyotes,
and jackals, and African wild dogs—are all more closely related to gray wolves than dire
wolves are. And since none of those things are classified
as wolves, that means dire wolves shouldn’t be either, at least not taxonomically. So they probably don’t belong in the genus
Canis alongside gray wolves. Instead, we might be better off using another,
older genus assigned to dire wolves in the past: Aenocyon. Aenocyon means “dreadful wolf,” so it’s
still suitably impressive. Since dire wolves and gray wolves are so distantly
related, the physical similarity between them seems to be a case of convergent evolution
-- two species evolving similar features in response to similar pressures. It wouldn’t be the only time evolution has
made a wolf. The extinct thylacine of Australia looks remarkably
like a canine -- even though it’s a marsupial. We asked Dr. Angela Perri, lead author of
the dire wolf study, why evolution seems to like wolves so much. She told us it’s hard to say, but it might
be that a wolf-like body is an ideal form for a predator. It’s the right size and shape to take down
large prey while also being energy efficient for hunting prey over long distances. But unraveling canine relationships doesn’t
just give us insight into dire wolf evolution -- it can also help us understand their extinction. One pretty obvious difference between gray
wolves and dire wolves is that gray wolves are still around. It could be that dire wolves, with their buff
bods, were specialized hunters who couldn’t survive once their large prey disappeared
at the end of the Ice Age. But this study presents another option: genetic
isolation. Canines today -- including wolves, coyotes,
domestic dogs, and more -- have a habit of interbreeding. This allows the species to exchange genes
and effectively expand their gene pools, which can make them more adaptable in the face of
change. For example, modern gray wolves are known
to have picked up genes related to immune response from domestic dogs. That might have helped the wolves resist diseases
carried by species migrating into the Americas at the end of the last Ice Age. But dire wolf DNA shows no signs of interbreeding
with those other species -- they were genetically isolated. It’s hard to know for sure, but if dire
wolves had been swapping genes with their fellow canines, they might have been more
adaptable, and we might still have them today… which would be lovely and terrifying. Given how similar gray wolves and dire wolves
look, it’s amazing how dramatically a little bit of DNA can change our understanding of
them. Fortunately, even if the genus changes, the
common name “dire wolf” is here to stay. Because honestly? It’s way too cool to get rid of. It only takes a little bit of new knowledge
to transform how we see the world. Around here, we’re all about learning -- but
so are our friends at Brilliant. For example, if you’re curious about how
we understand all this stuff, and how we incorporate new evidence, Brilliant has a bunch of courses
about logic and reasoning, starting with Logic I. It’ll teach you how to draw conclusions
from limited evidence without going off the rails. And if you really enjoy it, there are further
courses on logic and mathematical reasoning. If you’re interested, you can learn more,
and score 20% off an annual premium subscription, at brilliant.org/scishow. [♩OUTRO]
