Placeholder Image

字幕列表 影片播放

  • 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 wolvesaren'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 guyscoyotes, and jackals, and African wild dogsare 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 meansdreadful 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 namedire wolfis 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]

Thanks to Brilliant for supporting this episode of SciShow.

字幕與單字

影片操作 你可以在這邊進行「影片」的調整,以及「字幕」的顯示

B2 中高級 美國腔

可怕的狼是真实的!但不是狼(Dire Wolves Were Real! But Not Wolves)

  • 14 1
    joey joey 發佈於 2021 年 05 月 14 日
影片單字