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  • The non-avian dinosaursthe giants of the Mesozoicreached sizes no land mammal

  • has ever dreamed of.

  • There were massive meat-eaters, not to mention those long-necked herbivores.

  • But today's dinosaursthat is, birdsare a lot smaller.

  • I mean, the bee hummingbird is basically bee-sized, and it lays eggs the size of coffee beans.

  • So... did there used to be there tiny, non-avian dinos, too?

  • Well, there's somewhat of an ongoing debate in paleontology circles as to whether there

  • were lots of tiny dinosaur species, or whether non-avian dinosaur lineages were justbigger

  • overall.

  • But either way, we're pretty sure that there were at least some mini-dinosaurs scurrying

  • about in the Mesozoicbecause we've found their footprints.

  • The meter-long Microraptor was the smallest known dinosaur at the time of its discovery

  • in 1999.

  • Since then, we've found other, smaller fossilslike a specimen of Anchiornis whose body

  • mass was estimated to be a mere 110 grams.

  • It probably wasn't fully grown, though.

  • And that's probably as small as we'll ever findat least, in terms of fossilised

  • bones.

  • See, one of the reasons we don't see a lot of small dinosaurswhether they're juveniles

  • of larger animals or adults from small speciesis that there are biases in the fossil

  • record.

  • For a skeleton or body to fossilize, it has to be buried quickly in sediment, and not

  • destroyed or ripped apart by scavengers in the process.

  • And small bodies are generally more fragile, so they're less likely to survive being

  • buried.

  • Plus, small fossils aresmall.

  • They're not as obvious as, say, a T. rex femur sticking out of a cliffside.

  • And that may be why the smallest dinosaurs we have evidence for are ones we haven't

  • found at all.

  • Instead, they come from incredibly well-preserved footprints in South Korea.

  • Technically, these are ichnotaxa: the name paleontologists give to these trace fossils.

  • Because you can't technically name a dinosaur you haven't got, and you also can't connect

  • tracks to existing fossils with perfect certainty.

  • So, they name the footprints.

  • And one of them, Minisauripus, has been found in abundance.

  • In a 2019 paper, scientists published tracks so detailed that they preserved perfect impressions

  • of skin, complete with tiny, half-millimeter scales.

  • That was enough detail to be sure they weren't made by actual birds or their ancestors.

  • And nearly all of the Minisauripus tracks are less than three centimeters long.

  • While scientists are understandably reluctant to guess the size of something based on footprints

  • alone, the team estimated the track-maker to be about 28 centimeters long and weigh

  • only a few dozen gramsso, similar to a blackbird.

  • You might think these were just baby Velociraptors or somethingexcept the tracks are all

  • about the same size.

  • If they'd been made by juveniles, you'd expect a bunch of different sizes.

  • So it seems likely these track-makers were fully grown.

  • The same team has also published evidence for an even smaller dinoone that made

  • tracks just a centimeter long.

  • They dubbed these tracks Dromaeosauriformipes rarus, and they may have been made by a Velociraptor-like

  • dino that, when fully grown, was small enough to hold in your hands.

  • But, the team couldn't totally eliminate the possibility that the tracks were made

  • by hatchlings or juveniles rather than adults from a tiny species.

  • They say we'd need a skeleton to be certain.

  • And there's no guarantee we'll ever get one.

  • One thing's for sure, though: These footprints tell us that there were tiny dinosaurs living

  • alongside the massive ones we know so well.

  • And the more of them we find, the more we'll learn about the ecosystems of the past.

  • Thanks for watching this episode of SciShow, which is produced by Complexly.

  • If you enjoyed learning about these teeny little dinos, I have a feeling you'll enjoy

  • one of our other channels: PBS Eons.

  • PBS Eons explores the history of life on Earth, from the very first organisms in the Archaean

  • to the other human species that walked alongside us.

  • It's basically your chance to time travelwithout running afoul of any paradoxes.

  • If that sounds like your jam, you can head on over to

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B2 中上級

小さな恐竜はどこにいるの? (Where Are All the Tiny Dinosaurs?)

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    林宜悉 に公開 2021 年 01 月 14 日