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The secret weapon that let dinosaurs take over the planet

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    We've all heard about
    how the dinosaurs died.
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    The story I'm going to tell you
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    happened over 200 million years
    before the dinosaurs went extinct.
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    This story starts at the very beginning,
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    when dinosaurs were just
    getting their start.
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    One of the biggest mysteries
    in evolutionary biology
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    is why dinosaurs were so successful.
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    What led to their global dominance
    for so many years?
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    When people think about
    why dinosaurs were so amazing,
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    they usually think about the biggest
    or the smallest dinosaur,
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    or who was the fastest,
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    or who had the most feathers,
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    the most ridiculous armor,
    spikes or teeth.
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    But perhaps the answer had to do
    with their internal anatomy --
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    a secret weapon, so to speak.
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    My colleagues and I,
    we think it was their lungs.
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    I am both a paleontologist
    and a comparative anatomist,
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    and I am interested in understanding
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    how the specialized dinosaur lung
    helped them take over the planet.
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    So we are going to jump back
    over 200 million years
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    to the Triassic period.
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    The environment was extremely harsh,
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    there were no flowering plants,
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    so this means that there was no grass.
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    So imagine a landscape
    filled with all pine trees and ferns.
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    At the same time,
    there were small lizards,
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    mammals, insects,
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    and there were also carnivorous
    and herbivorous reptiles --
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    all competing for the same resources.
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    Critical to this story
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    is that oxygen levels have been estimated
    to have been as low as 15 percent,
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    compared to today's 21 percent.
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    So it would have been crucial
    for dinosaurs to be able to breathe
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    in this low-oxygen environment,
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    not only to survive
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    but to thrive and to diversify.
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    So, how do we know
    what dinosaur lungs were even like,
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    since all that remains of a dinosaur
    generally is its fossilized skeleton?
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    The method that we use is called
    "extant phylogenetic bracketing."
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    This is a fancy way of saying
    that we study the anatomy --
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    specifically in this case,
    the lungs and skeleton --
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    of the living descendants of dinosaurs
    on the evolutionary tree.
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    So we would look at the anatomy of birds,
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    who are the direct
    descendants of dinosaurs,
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    and we'd look at
    the anatomy of crocodilians,
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    who are their closest living relatives,
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    and then we would look at
    the anatomy of lizards and turtles,
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    who we can think of like their cousins.
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    And then we apply these anatomical data
    to the fossil record,
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    and then we can use that
    to reconstruct the lungs of dinosaurs.
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    And in this specific instance,
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    the skeleton of dinosaurs most closely
    resembles that of modern birds.
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    So, because dinosaurs were competing with
    early mammals during this time period,
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    it's important to understand
    the basic blueprint of the mammalian lung.
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    Also, to reintroduce you
    to lungs in general,
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    we will use my dog Mila of Troy,
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    the face that launched a thousand treats,
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    as our model.
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    (Laughter)
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    This story takes place
    inside of a chest cavity.
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    So I want you to visualize
    the ribcage of a dog.
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    Think about how
    the spinal vertebral column
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    is completely horizontal to the ground.
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    This is how the spinal
    vertebral column is going to be
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    in all of the animals
    that we'll be talking about,
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    whether they walked on two legs
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    or four legs.
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    Now I want you to climb inside
    of the imaginary ribcage and look up.
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    This is our thoracic ceiling.
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    This is where the top surface of the lungs
    comes into direct contact
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    with the ribs and vertebrae.
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    This interface is where
    our story takes place.
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    Now I want you to visualize
    the lungs of a dog.
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    On the outside, it's like
    a giant inflatable bag
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    where all parts of the bag
    expand during inhalation
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    and contract during exhalation.
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    Inside of the bag, there's a series
    of branching tubes,
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    and these tubes are called
    the bronchial tree.
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    These tubes deliver the inhaled oxygen
    to, ultimately, the alveolus.
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    They cross over a thin membrane
    into the bloodstream by diffusion.
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    Now, this part is critical.
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    The entire mammalian lung is mobile.
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    That means it's moving
    during the entire respiratory process,
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    so that thin membrane,
    the blood-gas barrier,
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    cannot be too thin or it will break.
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    Now, remember the blood-gas barrier,
    because we will be returning to this.
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    So, you're still with me?
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    Because we're going to start birds
    and it gets crazy,
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    so hold on to your butts.
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    (Laughter)
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    The bird is completely different
    from the mammal.
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    And we are going to be
    using birds as our model
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    to reconstruct the lungs of dinosaurs.
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    So in the bird,
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    air passes through the lung,
    but the lung does not expand or contract.
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    The lung is immobilized,
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    it has the texture of a dense sponge
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    and it's inflexible and locked into place
    on the top and sides by the ribcage
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    and on the bottom
    by a horizontal membrane.
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    It is then unidirectionally ventilated
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    by a series of flexible,
    bag-like structures
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    that branch off of the bronchial tree,
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    beyond the lung itself,
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    and these are called air sacs.
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    Now, this entire extremely delicate setup
    is locked into place
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    by a series of forked ribs
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    all along the thoracic ceiling.
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    Also, in many species of birds,
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    extensions arise from the lung
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    and the air sacs,
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    they invade the skeletal tissues --
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    usually the vertebrae,
    sometimes the ribs --
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    and they lock the respiratory
    system into place.
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    And this is called
    "vertebral pneumaticity."
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    The forked ribs and
    the vertebral pneumaticity
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    are two clues that we can hunt for
    in the fossil record,
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    because these two skeletal traits
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    would indicate that regions
    of the respiratory system of dinosaurs
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    are immobilized.
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    This anchoring of the respiratory system
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    facilitated the evolution
    of the thinning of the blood-gas barrier,
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    that thin membrane over which oxygen
    was diffusing into the bloodstream.
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    The immobility permits this
    because a thin barrier is a weak barrier,
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    and the weak barrier would rupture
    if it was actively being ventilated
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    like a mammalian lung.
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    So why do we care about this?
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    Why does this even matter?
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    Oxygen more easily diffuses
    across a thin membrane,
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    and a thin membrane is one way
    of enhancing respiration
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    under low-oxygen conditions --
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    low-oxygen conditions
    like that of the Triassic period.
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    So, if dinosaurs did indeed
    have this type of lung,
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    they'd be better equipped to breathe
    than all other animals,
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    including mammals.
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    So do you remember the extant
    phylogenetic bracket method
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    where we take the anatomy
    of modern animals,
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    and we apply that to the fossil record?
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    So, clue number one
    was the forked ribs of modern birds.
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    Well, we find that in pretty much
    the majority of dinosaurs.
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    So that means that the top surface
    of the lungs of dinosaurs
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    would be locked into place,
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    just like modern birds.
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    Clue number two is vertebral pneumaticity.
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    We find this in sauropod dinosaurs
    and theropod dinosaurs,
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    which is the group that contains
    predatory dinosaurs
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    and gave rise to modern birds.
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    And while we don't find evidence
    of fossilized lung tissue in dinosaurs,
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    vertebral pneumaticity gives us evidence
    of what the lung was doing
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    during the life of these animals.
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    Lung tissue or air sac tissue
    was invading the vertebrae,
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    hollowing them out
    just like a modern bird,
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    and locking regions
    of the respiratory system into place,
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    immobilizing them.
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    The forked ribs
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    and the vertebral pneumaticity together
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    were creating an immobilized,
    rigid framework
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    that locked the respiratory
    system into place
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    that permitted the evolution of that
    superthin, superdelicate blood-gas barrier
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    that we see today in modern birds.
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    Evidence of this straightjacketed
    lung in dinosaurs
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    means that they had
    the capability to evolve a lung
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    that would have been able to breathe
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    under the hypoxic, or low-oxygen,
    atmosphere of the Triassic period.
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    This rigid skeletal setup in dinosaurs
    would have given them
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    a significant adaptive advantage
    over other animals, particularly mammals,
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    whose flexible lung couldn't have adapted
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    to the hypoxic, or low-oxygen,
    atmosphere of the Triassic.
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    This anatomy may have been
    the secret weapon of dinosaurs
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    that gave them that advantage
    over other animals.
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    And this gives us an excellent launchpad
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    to start testing the hypotheses
    of dinosaurian diversification.
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    This is the story of
    the dinosaurs' beginning,
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    and it's just the beginning of the story
    of our research into this subject.
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    Thank you.
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    (Applause)
Title:
The secret weapon that let dinosaurs take over the planet
Speaker:
Emma Schachner
Description:

We've all heard the theories on how the dinosaurs died -- but why did they come to dominate the earth for so long in the first place? (Hint: it has nothing to do with their size, speed, spikes or fantastic feathers.) Travel back in time to 200 million years before their extinction with paleontologist Emma Schachner for a breath of fresh air on dinosaur history.

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Video Language:
English
Team:
TED
Project:
TEDTalks
Duration:
10:12

English subtitles

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