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  • Hi, this is Kate from MinuteEarth.

  • Paleontologists have long questioned why Tyrannosaurus Rex – a giant killing machine with 9-inch-long

  • daggers for teethhad such puny arms.

  • Were short arms particularly useful when grappling with prey, or when Sexy Rexy was in mating

  • mode?

  • Did they provide just the right leverage when getting up after a nap?

  • Maybe.

  • Like some evolutionary traits, from the gecko's camouflage, to the human's opposable thumb,

  • to the orchid's deceiving shape, perhaps those little limbs gave T. Rex some real advantage.

  • But it’s also quite possible that they didn’t.

  • For one thing, T. Rex might have ended up with small arms simply because big - or even

  • normal-sized - arms were a DISadvantage.

  • Perhaps once T-rex’s ancestors got big enough, they could hunt and eat with their giant jaws

  • aloneand their arms weren't worth the energy they took to haul around.

  • But evolution can’t just swap out not-so-useful traits for completely new ones.

  • Instead, over generations, T. rex’s arms may have simply gotten smaller and smaller

  • until there was no longer a significant cost to keeping them.

  • Then they just...stuck around - a lot like how we humans ended up with our tiny tailbones.

  • Another possibility is that evolution gave T. Rex tiny arms simply by chance, the same

  • way it gave Ireland lots and lots of redheads.

  • In a relatively small, isolated population, a trait that doesn’t hurt OR help an individual’s

  • chances of surviving and reproducing can, just by the luck of the draw, become more

  • and more prevalent from one generation to the next.

  • It’s possible that the size of T-rex’s arms didn’t matter much either, and all

  • the dinos just happened to end up with short arms.

  • On the other hand, weirdly-small arms have also evolved in other large T-rex relatives,

  • suggesting that the trait might not be totally random.

  • Right now, scientists are studying the microscopic wear and tear on the arm bones of the most

  • famous T-rex of all to determine how she used them.

  • This work might help us figure out if T. rex’s arms were useful like our thumbs, useless

  • like our tailbones, or random like our redheadedness.

  • Right now, the answer is still out of reach.

  • This video was sponsored by the University of Minnesota, where students, faculty and

  • staff across all fields of study are working to solve the Grand Challenges facing society.

  • University of Minnesota professors Suzanne McGaugh and Emma Goldberg, who advised us

  • on the science behind this video, investigate how several different mechanisms of evolution,

  • from adaptation to negative selection to genetic drift, affect traits -- like T. rex’s tiny

  • arms -- in a variety of species.

  • Professor Goldberg uses math to explore how a plant's reproductive traits affect its chances

  • at becoming new species or going extinct, and professor McGaugh rappels into Mexican

  • caves to better understand how blindness in cavefishes evolves independently in different

  • populations.

  • Thanks, University of Minnesota!

Hi, this is Kate from MinuteEarth.


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B1 中級

なぜTレックスはこんなに小さい腕を持っていたのか? (Why Did T Rex Have Such Tiny Arms?)

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    gotony5614.me97 に公開 2021 年 01 月 14 日