Placeholder Image

字幕列表 影片播放

  • 153 million years ago in Montana, the giant dinosaur known as Diplodocus wandered through

  • a seasonal wetland looking for its lunch.

  • Like most other sauropod dinosaurs, Diplodocus was pretty big - it weighed almost as much

  • as 4 elephants, and was about as long as three school buses.

  • And: a full 25% of that length was its neck, far longer than any mammal’s neck would

  • - or could - ever be.

  • If it sat back on its haunches to rear up, like some paleontologists have hypothesized

  • that it could have, then Diplodocus mightve reached a full 11 meters up into the trees.

  • So, you might understand why some paleontologists were surprised after studying the teeth of

  • a Diplodocus.

  • Based on the scratch marks they found on the teeth, it turned out that the primary diet

  • of Diplodocus wasn’t the leaves of trees; it was ground cover, like ferns and horsetails.

  • And it’s not just Diplodocus that ate this way.

  • Other sauropods that lived in the same area -- a region known today as the Morrison Formation

  • -- had unexpected diets, too.

  • Like, the 25 metric ton, 23 meter-long Apatosaurus, which also ate mostly ground-level plants.

  • Or the 15 meter long Camarasaurus, which ate tougher, shrub-sized plants and short trees

  • - despite being around 4 meters tall at the shoulder, which is almost two and a half Kallies

  • tall.

  • Each of these dinosaurs had a neck that was much longer than the animal was tall - way

  • longer than it needed to be for the dinosaur’s mouth to reach the ground.

  • But if so many sauropods were eating ground-level plants, why did they all have such long necks?

  • It turns out that it did give them a huge advantage when it came to food, but not in

  • the way you think.

  • And this benefit would allow them to become the biggest terrestrial animals of all time!

  • Being big comes with a fair number of advantages.

  • It makes you harder to attack and eat, for one.

  • And larger animals tend to lose heat more slowly, which means they can spend less energy

  • regulating their body temperature.

  • Bigger bodies can also store more energy for later, which helps them make it through tough

  • times.

  • They can also move farther, and faster, than most small bodies can - so they can survive

  • in environments where food sources are farther apart.

  • And if bigger is better, then sauropods were the best, as they became the largest animals

  • that ever walked on land.

  • Some, like Argentinosaurus from the Cretaceous of -- wait for it -- Argentina, got to be

  • 35 meters long and could have weighed up to 70 metric tons.

  • But while they would end up evolving to be absolutely enormous, the sauropod dinosaurs

  • had some pretty humble beginnings.

  • Sauropods are part of a larger group of dinosaurs called the sauropodomorphs, or sauropod-like

  • dinosaurs.

  • Scientists are still arguing about what the precise distinction is between the two.

  • But the most common definition is that once sauropodomorphs had to stand on all four legs

  • and stopped having grasping fingers, they were officially sauropods.

  • Still, all of the similarities between sauropods and sauropodomorphs means that it’s a little

  • hard to tell exactly when sauropods themselves evolved.

  • The first possible sauropod tracks show up toward the end of the Triassic Period, around

  • 210 million years ago, in North America.

  • But the earliest known definitely-probably-sauropod bones appear about 5 million years later in

  • Thailand.

  • And, based on those bones and the partial skeleton of another, slightly younger species,

  • paleontologists think that the first sauropods probably looked something like the Early Jurassic

  • dinosaur from Zimbabwe known as Vulcanodon

  • Vulcanodon was not as big as its later relatives, but it was a lot bigger than you: estimates

  • vary, but suggest it was around 9 or so meters long, and around 10 metric tons.

  • And it looked a lot like the sauropodomorphs that it coexisted with, having a somewhat

  • shorter neck and generally smaller body size than later sauropods.

  • But Vulcanodon had one subtle but important new feature:

  • Unlike other sauropodomorphs, its front legs were about as long as its back legs, and it

  • probably spent all of its time on all fours.

  • That shift to four-leggedness was an important glimpse of what was to come.

  • Being big requires a lot of stable support - and once they acquired the stability they

  • needed, they pretty quickly started to increase in size.

  • By the middle Jurassic, sauropods like Patagosaurus were almost twice the length of Vulcanodon.

  • But that was just the beginning.

  • By the end of the Jurassic, sauropods had become truly massive.

  • For example, Giraffatitan, was a 26-meter long monster from Tanzania, and is estimated

  • to have weighed as much as 78 tons.

  • And as sauropods got bigger and heftier, their necks did too.

  • The 10-meter long neck of Giraffatitan had nothing on the 15 meter long neck of Supersaurus,

  • the longest-necked sauropod found so far.

  • Now, paleontologists think that those long necks weren’t just some weird byproduct

  • of their large body size; instead, they actually made it possible for sauropods to become as

  • massive as they did.

  • The best-accepted hypothesis for why long necks evolved in the first place is that having

  • a long neck expanded a dinosaur’s feeding envelope.

  • Essentially, a feeding envelope is the space within which an animal can reach food without

  • having to move too much.

  • After all, moving consumes energyso the less you have to move in order to get to your

  • food, the better!

  • Maximizing your feeding efficiency is a key step for getting big, so long necks and big

  • bodies are pretty closely linked in sauropod dinosaurs.

  • There were, of course, always exceptions, but on the whole - the bigger the body, the

  • longer the neck.

  • Long necks were such a successful adaptation that, in the Late Jurassic, sauropods were

  • represented by 19 different genera worldwide.

  • And 10 of those can be found in the Morrison Formation in Montana, where Diplodocus and

  • many others lived.

  • But while long necks are a good clue that a sauropod was eating a lot, they aren’t

  • actually a good indication of what exactly it was eating.

  • Sure, there were sauropods that fed on tree-tops: Brachiosaurus, for example, had wear on its

  • teeth that matched well with a tree-munching lifestyle.

  • But the ones that ate at ground level like Diplodocus had equally long necks and big

  • bodies.

  • And while that might seem a little strange, it makes more sense when you understand the

  • environment that Diplodocus lived in.

  • It didn’t rain much in the Morrison Formation.

  • Instead, most water flowed in from nearby mountains, channeled by seasonal streams that

  • often flooded their banks.

  • Without rain, most of this big basin was home to an open, dry environment and very few trees.

  • Scientists compare it to a savannah - but with cycads and short ferns, instead of grass,

  • which hadn’t evolved yet.

  • But the low-lying areas formed small lakes and vast wetlands, and these were ringed with

  • trees.

  • So all of these different environments meant that the Morrison could support those 10 different

  • genera of sauropods - because they were eating different things and living in slightly different

  • places.

  • For example, the high-browsing Brachiosaurus and shrub-eating Camarasaurus likely spent

  • most of their time eating trees that grew near the lakes and streams.

  • But Diplodocus was eating plants that grew in the wetlands.

  • And, if youre a large dinosaur, wetlands aren’t a very safe place.

  • Getting stuck in the mud and having to fight your way back out wouldve been exhausting

  • and potentially deadly.

  • In fact, some muddy rocks of the Morrison Formation seem to preserve sauropods that

  • died in just this way!

  • But Diplodocus’s long neck made it easy to reach deep into these wetlands and eat

  • ferns and other plants without ever getting its toes muddy.

  • As a result, Diplodocus was able to access food that other large herbivores like Stegosaurus

  • couldn’t, and carve out a space for itself where it didn’t compete with other herbivores.

  • So long sauropod necks for the win: They allowed some of these giant dinos to have a huge feeding

  • envelope - even if for some of them, that envelope was, horizontal, rather than vertical.

  • And necks are one area where the current ruling class of animals, the mammals, will never

  • be better than the dinosaurs.

  • The giraffe, of course, has the longest neck of any living mammal.

  • But it’s only about a third as long as a Diplodocus neckand there’s one big

  • constraint that no giraffe in the past or future can overcome.

  • Almost all mammals, including you and giraffes, have only 7 neck vertebrae.

  • Instead of having more bones in their necks, giraffes just have longer ones.

  • But, sauropods and other dinosaurs didn’t have that limitation.

  • They could have up to 19 vertebrae in their necks!

  • That’s why, today, the surviving dinosaurs -- also known as birds -- are the ones carrying

  • on that long-necked tradition.

  • Birds have even more uses for their necks than sauropods did.

  • They use them for specialized feeding in wetlands, for preening their hind feathers, and for

  • helping their heads stay level as they walk and fly.

  • Some birds, like parrots, even use their necks as an additional limb to help them climb trees.

  • And if were just counting the number of vertebrae, today’s dinosaurs have the extinct

  • ones totally beat: Some birds have up to 25 vertebrae in their necks!

  • But, lucky for us, those long-necked birds haven’t evolved to contend with sauropods

  • for the title of biggest dinosaur.

  • A regular sized goose is bad enough - but one the size of a Supersaurus?

  • No thank you.

  • Ready to increase your digital feeding envelope?

  • Be sure to check out PBS Digital Studiosnew food channel, PBS Zest!— all about exploring

  • food through culture, community and science.

  • Its new series, Good Gumbo, dives deep to uncover the stories (and cultures) behind

  • iconic southern foods; Serving up Science delivers research-backed tips to make your

  • favorite foods even tastier.

  • Fair warning

  • This channel might make you hungry...

  • Also extra long high-fives to this month’s Eontologists: Patrick Seifert, Jake Hart,

  • Jon Davison Ng, Sean Dennis, Hollis, and Steve!

  • To become an Eonite, pledge your support at patreon.com/eons!

  • And as always, thank you for joining me in the Konstantin Haase Studio.

  • Be sure to subscribe at youtube.com/eons!

153 million years ago in Montana, the giant dinosaur known as Diplodocus wandered through

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

关于梁龙长颈的短篇小说(A Short Tale About Diplodocus' Long Neck)

  • 2 1
    joey joey 發佈於 2021 年 05 月 01 日
影片單字