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  • Thanks to Brilliant for supporting this episode of SciShow.

  • Go to Brilliant.org/SciShow to learn more.

  • [ intro ]

  • Now we all know that there is lot's of important infectious disease science

  • happening right now

  • and three cheers for the people doing that work.

  • So do today for Scishow News, there will be breaking news, but it will be very, very old.

  • It was during the Late Devonian Period,

  • over360 million years ago,

  • that one group of fish evolved feet from fins,

  • and moved from water to land.

  • This gave rise to a group called the tetrapods,

  • which today includes all amphibians, reptiles, birds, and mammals --

  • from herons to hippos to humans.

  • A new study published in the journal Nature

  • describes how an ancient fish represents a crucial stage in that transition.

  • And for scientists interested in understanding

  • how our tetrapod bodies came to be,

  • this new specimen is proving to be veryhandy.

  • It's called Elpistostege watsoni.

  • It's not a new species, but this new fossil, found in Quebec in 2010,

  • is one of the most complete skeletons known of any early tetrapod relative.

  • See, this grand evolutionary transition

  • is mostly understood through a handful of Late Devonian animals

  • that blur the line between fish and tetrapods.

  • Some, like Eusthenopteron,

  • are basically fish with very tetrapod-like features,

  • such as well-developed limb bones.

  • Others, such as the famous four-legged Acanthostega,

  • are considered true early tetrapods that still have very fishy bodies.

  • But many of these fossils are incomplete,

  • leaving gaps in our understanding

  • of how certain parts of the body changed over this transition.

  • This new Elpistostege specimen is well preserved from its head to its tail,

  • but in this study, the researchers were particularly interested in its front fins.

  • That's because one of the most important defining features of true tetrapods

  • is the presence of digits --

  • that is, finger bones.

  • Elpistostege is still fairly fishy, though.

  • And as you might expect from a fish,

  • its front fins ended in thin bony rays.

  • Using an x-ray imaging procedure that provided a peek at the internal structure of the fins,

  • they found that the bones inside were arranged very much like the digits in our own hands.

  • It wasn't quite a hand,

  • but it was basically a fish fin with the bones of a hand hidden inside!

  • In fact, the researchers say this is the most tetrapod-like bone arrangement

  • of any fish fin yet studied.

  • This means that Elpistostege sits at a very important place

  • in our own family tree,

  • a very close cousin of the earliest true tetrapods.

  • And the fact that it had well-developed hand bones

  • inside a functional fish fin

  • supports the idea that the tetrapod limb developed in the water.

  • It might be that these bones

  • provided extra strength for fish crawling around in shallow water,

  • or maybe even for short forays onto land --

  • setting up the ability to move to land more permanently in its descendants.

  • This new fossil gives us a clearer picture

  • of exactly when and where certain changes took place

  • along this fish-to-tetrapod transition,

  • which will hopefully guide future fossil research as well.

  • Meanwhile, another new fossil described in Nature

  • sheds light on the early evolution of a much later group of tetrapods: birds!

  • This ancient bird comes from the Late Cretaceous of Belgium,

  • between 66.7 and 66.8 million years ago,

  • right around the end of the Age of Dinosaurs.

  • The fossil consists of an extremely well-preserved skull

  • along with some bones of the body,

  • with enough unique features for researchers to identify it as a new species:

  • Asteriornis maastrichtensis.

  • Based on its anatomy, the paleontologists classify it as an early cousin

  • of a group of birds called the Galloanserae,

  • which today includes landfowl and waterfowl,

  • including turkeys, chickens, ducks, and geese.

  • In fact, some have dubbed it the Wonderchicken.

  • Its skull has a mixture of landfowl-like and waterfowl-like features.

  • But beyond that,

  • this identification makes Asteriornis

  • the oldest known member of a /living/ group of birds.

  • See, while there are lots of fossil birds known from the Cretaceous Period,

  • they mostly belong to ancient groups that went extinct along with the rest of the dinosaurs.

  • This means Asteriornis also gives us a very rare glimpse at the early evolution of modern

  • bird diversity --

  • not only what they looked like, but where they lived.

  • Much of the diversity of modern birds clusters in the southern continents, so some scientists

  • have proposed that the early evolution of modern birds took place in the south.

  • But Asteriornis, being from Belgium, muddies the picture.

  • One the one hand,

  • this means we might be wrong about where modern birds got their start.

  • But on the other,

  • now we know that Europe might be a good place to look for more fossil clues.

  • And while scientists are trying to understand where these birds lived,

  • they also want to know how they even survived to the present day.

  • Because we're not sure why specific lineages

  • did/ make it through the end-Cretaceous extinction.

  • Scientists have suggested that the ancestors of modern birds

  • may have had a few features that helped them along:

  • small body size would mean they didn't need much food,

  • and a generalized diet would mean they weren't picky eaters --

  • both good traits to have in an apocalypse.

  • Asteriornis is indeed a small bird,

  • with an estimated mass under 400 grams.

  • And it was discovered on an ancient shoreline,

  • which means it /might/ have lived a not-very-picky lifestyle like modern-day shorebirds.

  • Of course, this one fossil doesn't answer any of these questions for sure, but --

  • like the new Elpistostege fossil --

  • it gives us a renewed idea of where to look,

  • and what to look for, to find more pieces of these ancient puzzles.

  • And if you like puzzles, you're really going to like Brilliant.

  • Like their course on Calculus in a Nutshell.

  • If you've been wondering what an integral is

  • and what the heck to do with one, wonder no more.

  • This course takes a bird's eye view of the subject,

  • from limits to derivatives.

  • And it shows how everyone from economists to urban planners use calculus every day.

  • The idea is to help you develop an intuitive understanding of how calc works,

  • instead of making you memorize a bunch of formulas with a bunch of Greek letters.

  • So if you're curious about math, this is designed to help you learn.

  • And as it happens,

  • the first 200 people to sign up at Brilliant.org/SciShow

  • will get 20% off an annual Premium subscription.

  • We're not saying it's something to do while everyone is stuck inside socially distancing,

  • but we're not not saying that, either.

  • So check it out and see if it's right for you --

  • and thanks for your support.

  • [ outro ]

Thanks to Brilliant for supporting this episode of SciShow.

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B1 中級

一個非常方便的魚化石 (A Very Handy Fish Fossil)

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    林宜悉 發佈於 2021 年 01 月 14 日
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