The secret weapon that let dinosaurs take over the planet | Emma Schachner

Translator: Joseph Geni Reviewer: Camille Martínez

翻译人员: Gabriella Hu 校对人员: Yolanda Zhang

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

我接下来要讲的故事

happened over 200 million years before the dinosaurs went extinct.

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,

这个故事要从头开始，

when dinosaurs were just getting their start.

那时恐龙刚刚开始繁衍。

One of the biggest mysteries in evolutionary biology

进化生物学最大的谜团之一

is why dinosaurs were so successful.

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,

当人们感叹恐龙的神奇时，

they usually think about the biggest or the smallest dinosaur,

他们通常会联想到 体型最大或最小的恐龙，

or who was the fastest,

或是速度最快的，

or who had the most feathers,

或是羽翼最丰满的，

the most ridiculous armor, spikes or teeth.

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 --

但是答案也许是它们的身体结构——

a secret weapon, so to speak.

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

我十分想了解恐龙如何用

how the specialized dinosaur lung helped them take over the planet.

它们特殊的肺来称霸地球。

So we are going to jump back over 200 million years

我们现在要倒退到两亿年前的

to the Triassic period.

三叠纪时代。

The environment was extremely harsh,

那里的环境十分严酷，

there were no flowering plants,

没有开花的植物，

so this means that there was no grass.

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,

同时，还有小型蜥蜴，

mammals, insects,

哺乳动物，昆虫，

and there were also carnivorous and herbivorous reptiles --

而且还有食肉和食草 的爬虫类动物——

all competing for the same resources.

都在为相同的资源而竞争。

Critical to this story

这个故事还有重要的一点，

is that oxygen levels have been estimated to have been as low as 15 percent,

就是当时的大气层中 的氧气含量只有 15%，

compared to today's 21 percent.

现在则是 21%。

So it would have been crucial for dinosaurs to be able to breathe

所以对恐龙来说， 在这种低氧环境中呼吸

in this low-oxygen environment,

是至关重要的，

not only to survive

不仅仅为了生存，

but to thrive and to diversify.

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 --

这只是一个专业名词， 意思是我们研究的生物结构——

specifically in this case, the lungs and skeleton --

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,

于是我们会研究鸟类的生物结构，

who are the direct descendants of dinosaurs,

也就是恐龙的直接后代，

and we'd look at the anatomy of crocodilians,

我们还会研究鳄鱼，

who are their closest living relatives,

它们是恐龙最近的亲戚，

and then we would look at the anatomy of lizards and turtles,

还有蜥蜴和龟类，

who we can think of like their cousins.

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,

在这个例子中，

the skeleton of dinosaurs most closely resembles that of modern birds.

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,

为了让你们重新熟悉肺结构，

we will use my dog Mila of Troy,

我就用我的狗狗米拉——

the face that launched a thousand treats,

它可爱到可以骗取无数零食——

as our model.

来做模型。

(Laughter)

（笑声）

This story takes place inside of a chest cavity.

我们先来看看胸腔结构。

So I want you to visualize the ribcage of a dog.

我想让你们先想象一下 一只狗的肋骨。

Think about how the spinal vertebral column

设想脊椎和脊柱

is completely horizontal to the ground.

是和地面平行的。

This is how the spinal vertebral column is going to be

我们接下来要讲的 所有动物的脊椎脊柱

in all of the animals that we'll be talking about,

和这个是一样的，

whether they walked on two legs

无论是两条腿走路的

or four legs.

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

在这里我们的肺的最上部 会和肋骨，脊椎

with the ribs and vertebrae.

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

吸气时会膨胀，

and contract during exhalation.

呼气时会收缩。

Inside of the bag, there's a series of branching tubes,

在袋子里面有一系列的分支气管，

and these tubes are called the bronchial tree.

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.

这一步很关键。

The entire mammalian lung is mobile.

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,

所以那层血气屏障

cannot be too thin or it will break.

如果太薄的话容易破损。

Now, remember the blood-gas barrier, because we will be returning to this.

我们等会儿还要回到那层薄膜。

So, you're still with me?

你们还跟得上吗？

Because we're going to start birds and it gets crazy,

我们现在开始要讲鸟类了，

so hold on to your butts.

准备好。

(Laughter)

（笑声）

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

我们要用鸟类作为模型来

to reconstruct the lungs of dinosaurs.

重造恐龙的肺。

So in the bird,

在鸟类中，

air passes through the lung, but the lung does not expand or contract.

空气通过肺， 但是肺部并不会膨胀或收缩，

The lung is immobilized,

它们的肺是无法移动的，

it has the texture of a dense sponge

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

在肋骨的顶部和侧面都有连接， 还有底部水平的薄膜，

and on the bottom by a horizontal membrane.

导致肺无法移动。

It is then unidirectionally ventilated

有一系列灵活的袋状结构

by a series of flexible, bag-like structures

为它们的肺提供单向通风，

that branch off of the bronchial tree,

这些结构从支气管树延伸

beyond the lung itself,

到肺部的外面，

and these are called air sacs.

它们叫做气囊。

Now, this entire extremely delicate setup is locked into place

这个错综复杂的结构沿胸腔顶部

by a series of forked ribs

被一系列

all along the thoracic ceiling.

分叉的肋骨锁定到位。

Also, in many species of birds,

而且，在许多鸟类体内，

extensions arise from the lung

肺部上方以及气囊包含

and the air sacs,

的延伸的结构

they invade the skeletal tissues --

会扩张到骨骼组织中——

usually the vertebrae, sometimes the ribs --

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

这些分叉的肋骨和椎体气动性

are two clues that we can hunt for in the fossil record,

是两个在化石中有迹可循的线索，

because these two skeletal traits

因为这两个骨骼特征

would indicate that regions of the respiratory system of dinosaurs

表明恐龙的呼吸系统

are immobilized.

也是不可移动的。

This anchoring of the respiratory system

呼吸系统的不可移动性

facilitated the evolution of the thinning of the blood-gas barrier,

推动了血气屏障—— 也就是那层协助氧气

that thin membrane over which oxygen was diffusing into the bloodstream.

扩散到血液中的薄膜—— 朝着变薄的方向进化。

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

那层薄膜在十分通风的情况下 很容易破裂，

like a mammalian lung.

就像哺乳类动物的肺 所处的环境一样。

So why do we care about this?

我们为什么要关心这个呢？

Why does this even matter?

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

薄膜是在低氧环境下

under low-oxygen conditions --

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,

它们就比别的动物 具备更好的呼吸系统，

including mammals.

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,

也就是我们用现代动物的构造

and we apply that to the fossil record?

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

这意味着恐龙的肺的顶部

would be locked into place,

是锁定到位的，

just like modern birds.

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

也就是掠食性恐龙中， 都可以找到，

and gave rise to modern birds.

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

但椎体气动性可以告诉我们 恐龙存活时

during the life of these animals.

肺的大致功能。

Lung tissue or air sac tissue was invading the vertebrae,

肺组织和气囊组织侵入椎骨中，

hollowing them out just like a modern bird,

使其变成空心，就如现代鸟类一样，

and locking regions of the respiratory system into place,

使部分呼吸系统锁定在位，

immobilizing them.

让肺无法移动。

The forked ribs

分叉的肋骨

and the vertebral pneumaticity together

和椎体气动性一起

were creating an immobilized, rigid framework

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

使得我们今天在现代鸟类身上 看到的超薄、超脆弱

that we see today in modern birds.

的血气屏障得以进化。

Evidence of this straightjacketed lung in dinosaurs

恐龙有不可移动肺的证据

means that they had the capability to evolve a lung

意味着它们可以演化出一个

that would have been able to breathe

能在低氧环境中呼吸的肺，

under the hypoxic, or low-oxygen, 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

这样的肺结构使它们

a significant adaptive advantage over other animals, particularly mammals,

与其他动物，尤其是哺乳类动物相比， 有巨大的适应性优势，

whose flexible lung couldn't have adapted

因为其他动物可移动的肺

to the hypoxic, or low-oxygen, atmosphere of the Triassic.

无法适应三叠纪的低氧环境。

This anatomy may have been the secret weapon of dinosaurs

这样的生物结构也许 就是恐龙的秘密武器，

that gave them that advantage over other animals.

可以带给它们巨大的生存优势。

And this gives us an excellent launchpad

这也为我们去测试恐龙多样化

to start testing the hypotheses of dinosaurian diversification.

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.

也只是我们在这一领域研究的开端。

Thank you.

谢谢。

(Applause)

（掌声）