We've all heard about how the dinosaurs died.
我们都听说过恐龙是如何灭绝的。
The story I'm going to tell you happened over 200 million years before the dinosaurs went extinct.
我接下来要讲的故事发生在超过两亿年前恐龙还未灭绝的时候。
This story starts at the very beginning, when dinosaurs were just getting their start.
这个故事要从头开始，那时恐龙刚刚开始繁衍。
One of the biggest mysteries in evolutionary biology is why dinosaurs were so successful.
进化生物学最大的谜团之一就是恐龙为什么那么成功。
What led to their global dominance for so many years?
它们如何在地球上称霸多年？
When people think about why dinosaurs were so amazing, they usually think about the biggest or the smallest dinosaur,
当人们感叹恐龙的神奇时，他们通常会联想到体型最大或最小的恐龙，
or who was the fastest, or who had the most feathers, the most ridiculous armor, spikes or teeth.
或是速度最快的，或是羽翼最丰满的，有着最奇异的铠甲、尖刺或利齿的。
But perhaps the answer had to do with their internal anatomy -- a secret weapon, so to speak.
但是答案也许是它们的身体结构--这种所谓的秘密武器。
My colleagues and I, we think it was their lungs.
我和同事们都认为是它们的肺。
I am both a paleontologist and a comparative anatomist,
我是一名古生物学家，也是一名比较解剖学家，
and I am interested in understanding how the specialized dinosaur lung helped them take over the planet.
我十分想了解恐龙如何用它们特殊的肺来称霸地球。
So we are going to jump back over 200 million years to the Triassic period.
我们现在要倒退到两亿年前的三叠纪时代。
The environment was extremely harsh, there were no flowering plants, so this means that there was no grass.
那里的环境十分严酷，没有开花的植物，也就意味着没有草。
So imagine a landscape filled with all pine trees and ferns.
想象一片只有松树和蕨类的土地。
At the same time, there were small lizards, mammals, insects,
同时，还有小型蜥蜴，哺乳动物，昆虫，
and there were also carnivorous and herbivorous reptiles -- all competing for the same resources.
而且还有食肉和食草的爬虫类动物--都在为相同的资源而竞争。
Critical to this story is that oxygen levels have been estimated to have been as low as 15 percent, compared to today's 21 percent.
这个故事还有重要的一点，就是当时的大气层中的氧气含量只有15%，现在则是21%。
So it would have been crucial for dinosaurs to be able to breathe in this low-oxygen environment,
所以对恐龙来说，在这种低氧环境中呼吸是至关重要的，
not only to survive but to thrive and to diversify.
不仅仅为了生存，还要能繁衍和多样化。
So, how do we know what dinosaur lungs were even like,
那我们是如何知道恐龙的肺长什么样子呢，
since all that remains of a dinosaur generally is its fossilized skeleton?
它们遗留下来的只有化石骨架了。
The method that we use is called "extant phylogenetic bracketing."
我们采用的方法是“现存系统发育分组”。
This is a fancy way of saying that we study the anatomy -- specifically in this case, the lungs and skeleton
这只是一个专业名词，意思是我们研究的生物结构--在这个例子中，尤其是肺和骨架，
of the living descendants of dinosaurs on the evolutionary tree.
来自于恐龙在进化树中现存的后裔。
So we would look at the anatomy of birds, who are the direct descendants of dinosaurs,
于是我们会研究鸟类的生物结构，也就是恐龙的直接后代，
and we'd look at the anatomy of crocodilians, who are their closest living relatives,
我们还会研究鳄鱼，它们是恐龙最近的亲戚，
and then we would look at the anatomy of lizards and turtles, who we can think of like their cousins.
还有蜥蜴和龟类，它们也算是恐龙的表兄弟。
And then we apply these anatomical data to the fossil record,
然后我们把这些生物结构数据应用到化石记录中，
and then we can use that to reconstruct the lungs of dinosaurs.
这样我们就可以重建恐龙的肺结构。
And in this specific instance, the skeleton of dinosaurs most closely resembles that of modern birds.
在这个例子中，恐龙的骨架和鸟类最相似。
So, because dinosaurs were competing with early mammals during this time period,
因为在远古时代恐龙曾和哺乳动物竞争，
it's important to understand the basic blueprint of the mammalian lung.
那么了解哺乳动物的肺结构就尤为重要。
Also, to reintroduce you to lungs in general, we will use my dog Mila of Troy,
为了让你们重新熟悉肺结构，我就用我的狗狗米拉，
the face that launched a thousand treats, as our model.
它可爱到可以骗取无数零食，来做模型。
This story takes place inside of a chest cavity. So I want you to visualize the ribcage of a dog.
我们先来看看胸腔结构。我想让你们先想象一下一只狗的肋骨。
Think about how the spinal vertebral column is completely horizontal to the ground.
设想脊椎和脊柱是和地面平行的。
This is how the spinal vertebral column is going to be in all of the animals that we'll be talking about,
我们接下来要讲的所有动物的脊椎脊柱和这个是一样的，
whether they walked on two legs or four legs.
无论是两条腿走路的还是四条腿。
Now I want you to climb inside of the imaginary ribcage and look up.
想象我们在胸腔内部，然后朝上看。
This is our thoracic ceiling.
那是我们的胸椎顶部。
This is where the top surface of the lungs comes into direct contact with the ribs and vertebrae.
在这里我们的肺的最上部会和肋骨，脊椎有直接接触。
This interface is where our story takes place.
这个界面就是我们要讨论的地方。
Now I want you to visualize the lungs of a dog.
现在你们可以想象一只狗的肺。
On the outside, it's like a giant inflatable bag
在外面看似一个巨大的充气袋子，
where all parts of the bag expand during inhalation and contract during exhalation.
吸气时会膨胀，呼气时会收缩。
Inside of the bag, there's a series of branching tubes, and these tubes are called the bronchial tree.
在袋子里面有一系列的分支气管，这些气管叫做支气管树。
These tubes deliver the inhaled oxygen to, ultimately, the alveolus.
这些气管把吸入的氧气运送到肺泡。
They cross over a thin membrane into the bloodstream by diffusion.
氧气再穿过一层薄膜扩散进入血流。
Now, this part is critical. The entire mammalian lung is mobile.
这一步很关键。哺乳类动物的整个肺是可移动的。
That means it's moving during the entire respiratory process,
这意味着在整个呼吸过程中它都在移动，
so that thin membrane, the blood-gas barrier, cannot be too thin or it will break.
所以那层血气屏障如果太薄的话容易破损。

Now, remember the blood-gas barrier, because we will be returning to this. So, you're still with me?
请记住它，我们等会儿还要回到那层薄膜。你们还跟得上吗？
Because we're going to start birds and it gets crazy, so hold on to your butts.
我们现在开始要讲鸟类了，准备好。
The bird is completely different from the mammal.
鸟类和哺乳类动物完全不一样。
And we are going to be using birds as our model to reconstruct the lungs of dinosaurs.
我们要用鸟类作为模型来重造恐龙的肺。
So in the bird, air passes through the lung, but the lung does not expand or contract.
在鸟类中，空气通过肺，但是肺部并不会膨胀或收缩。
The lung is immobilized, it has the texture of a dense sponge
它们的肺是无法移动的，质地和一块厚海绵一样，
and it's inflexible and locked into place on the top and sides by the ribcage and on the bottom by a horizontal membrane.
在肋骨的顶部和侧面都有连接，还有底部水平的薄膜，导致肺无法移动。
It is then unidirectionally ventilated by a series of flexible, bag-like structures
有一系列灵活的袋状结构为它们的肺提供单向通风，
that branch off of the bronchial tree, beyond the lung itself, and these are called air sacs.
这些结构从支气管树延伸到肺部的外面，它们叫做气囊。
Now, this entire extremely delicate setup is locked into place by a series of forked ribs all along the thoracic ceiling.
这个错综复杂的结构沿胸腔顶部被一系列分叉的肋骨锁定到位。
Also, in many species of birds, extensions arise from the lung and the air sacs,
而且，在许多鸟类体内，肺部上方以及气囊包含的延伸的结构
they invade the skeletal tissues -- usually the vertebrae, sometimes the ribs
会扩张到骨骼组织中--通常是椎骨，有时是肋骨，
and they lock the respiratory system into place.
它们让整个呼吸系统得到固定。
And this is called "vertebral pneumaticity."
这个结构叫做“椎体气动性”。
The forked ribs and the vertebral pneumaticity are two clues that we can hunt for in the fossil record,
这些分叉的肋骨和椎体气动性是两个在化石中有迹可循的线索，
because these two skeletal traits would indicate that regions of the respiratory system of dinosaurs are immobilized.
因为这两个骨骼特征表明恐龙的呼吸系统也是不可移动的。
This anchoring of the respiratory system facilitated the evolution of the thinning of the blood-gas barrier,
呼吸系统的不可移动性推动了血气屏障朝着变薄的方向进化，
that thin membrane over which oxygen was diffusing into the bloodstream.
也就是那层协助氧气扩散到血液中的薄膜。
The immobility permits this because a thin barrier is a weak barrier,
肺的不可移动性可以使那层薄膜变得脆弱，
and the weak barrier would rupture if it was actively being ventilated like a mammalian lung.
那层薄膜在十分通风的情况下很容易破裂，就像哺乳类动物的肺所处的环境一样。
So why do we care about this? Why does this even matter?
我们为什么要关心这个呢？有什么意义吗？
Oxygen more easily diffuses across a thin membrane,
氧气更容易通过薄膜扩散，
and a thin membrane is one way of enhancing respiration under low-oxygen conditions
薄膜是在低氧环境下提高呼吸率的一种办法，
low-oxygen conditions like that of the Triassic period.
比如三叠纪的低氧环境中。
So, if dinosaurs did indeed have this type of lung,
如果恐龙的确有这种肺结构，
they'd be better equipped to breathe than all other animals, including mammals.
它们就比别的动物具备更好的呼吸系统，包括哺乳动物。
So do you remember the extant phylogenetic bracket method
你们还记得现存系统发育分组法吗，
where we take the anatomy of modern animals, and we apply that to the fossil record?
也就是我们用现代动物的构造来应用到化石记录中。
So, clue number one was the forked ribs of modern birds.
线索一就是现代鸟类的分叉的肋骨。
Well, we find that in pretty much the majority of dinosaurs.
这一点在几乎所有恐龙中都可以找到。
So that means that the top surface of the lungs of dinosaurs would be locked into place, just like modern birds.
这意味着恐龙的肺的顶部是锁定到位的，就像现存的鸟类一样。
Clue number two is vertebral pneumaticity.
线索二是椎体气动性。
We find this in sauropod dinosaurs and theropod dinosaurs,
我们在蜥脚类恐龙和兽脚类恐龙，
which is the group that contains predatory dinosaurs and gave rise to modern birds.
也就是掠食性恐龙中，都可以找到，它们也就是现代鸟类的祖先。
And while we don't find evidence of fossilized lung tissue in dinosaurs,
虽然我们没有恐龙的肺化石，
vertebral pneumaticity gives us evidence of what the lung was doing during the life of these animals.
但椎体气动性可以告诉我们恐龙存活时肺的大致功能。
Lung tissue or air sac tissue was invading the vertebrae, hollowing them out just like a modern bird,
肺组织和气囊组织侵入椎骨中，使其变成空心，就如现代鸟类一样，
and locking regions of the respiratory system into place, immobilizing them.
使部分呼吸系统锁定在位，让肺无法移动。
The forked ribs and the vertebral pneumaticity together were creating an immobilized, rigid framework
分叉的肋骨和椎体气动性一起创造了一个无法移动的、坚硬的构架，
that locked the respiratory system into place
把整个呼吸系统锁定到位，
that permitted the evolution of that superthin, superdelicate blood-gas barrier that we see today in modern birds.
使得我们今天在现代鸟类身上看到的超薄、超脆弱的血气屏障得以进化。
Evidence of this straightjacketed lung in dinosaurs means that
恐龙有不可移动肺的证据意味着
they had the capability to evolve a lung that would have been able to breathe under the hypoxic, or low-oxygen,
它们可以演化出一个能在低氧环境中呼吸的肺，
atmosphere of the Triassic period.
让它们在三叠纪大气层中得以存活。
This rigid skeletal setup in dinosaurs would have given them a significant adaptive advantage over other animals,
这样的肺结构使它们与其他动物相比有巨大的适应性优势，
particularly mammals, whose flexible lung couldn't have adapted to the hypoxic, or low-oxygen, atmosphere of the Triassic.
尤其是哺乳类动物相比，因为其他动物可移动的肺无法适应三叠纪的低氧环境。
This anatomy may have been the secret weapon of dinosaurs that gave them that advantage over other animals.
这样的生物结构也许就是恐龙的秘密武器，可以带给它们巨大的生存优势。
And this gives us an excellent launchpad to start testing the hypotheses of dinosaurian diversification.
这也为我们去测试恐龙多样化的假设提供了良好的基石。
This is the story of the dinosaurs' beginning,
这就是恐龙生存繁衍的故事，
and it's just the beginning of the story of our research into this subject. Thank you.
也只是我们在这一领域研究的开端。谢谢。