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

Translator: Joseph Geni Reviewer: Camille Martínez

譯者: Lilian Chiu 審譯者: Helen Chang

We've all heard about how the dinosaurs died.

我們都聽過恐龍是怎麼滅絕的。

The story I'm going to tell you

我要告訴各位的故事

happened over 200 million years before the dinosaurs went extinct.

發生的時間至少在 恐龍絕種前兩億年。

This story starts at the very beginning,

故事開始於最早的時期，

when dinosaurs were just getting their start.

恐龍剛剛發跡時。

One of the biggest mysteries in evolutionary biology

演化生物學中最大的謎題之一

is why dinosaurs were so successful.

就是為什麼恐龍能如此成功。

What led to their global dominance for so many years?

是什麼讓牠們能 主宰全球這麼多年？

When people think about why dinosaurs were so amazing,

談到為什麼恐龍如此了不起時，

they usually think about the biggest or the smallest dinosaur,

通常大家會想到最大或最小的恐龍，

or who was the fastest,

或者哪種恐龍最快，或羽毛最多，

or who had the most feathers,

the most ridiculous armor, spikes or teeth.

或者最可笑的裝甲、尖刺，或牙齒。

But perhaps the answer had to do with their internal anatomy --

但也許，答案和牠們的 內部解剖結構有關——

a secret weapon, so to speak.

可以說是一種秘密武器。

My colleagues and I, we think it was their lungs.

我和我同事認為 關鍵在牠們的肺部。

I am both a paleontologist and a comparative anatomist,

我是古生物學家， 也是比較解剖學家，

and I am interested in understanding

我感興趣的是了解

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

特殊化的恐龍肺部 如何協助牠們掌管地球。

So we are going to jump back over 200 million years

所以，我們要回到超過兩億年前，

to the Triassic period.

三疊紀時期。

The environment was extremely harsh,

當時的環境非常嚴酷，

there were no flowering plants,

沒有會開花的植物，

so this means that there was no grass.

這就表示也沒有草。

So imagine a landscape filled with all pine trees and ferns.

想像一片滿是松樹 和蕨類植物的地景，

At the same time, there were small lizards,

同時，還有小型蜥蜴、

mammals, insects,

哺乳類動物、昆蟲，

and there were also carnivorous and herbivorous reptiles --

還有肉食性和草食性的爬蟲類——

all competing for the same resources.

全都要競爭搶奪同樣的資源。

Critical to this story

對這個故事很重要的一點是

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

估計當時的氧含量只有 15% 這麼低，

compared to today's 21 percent.

相對之下，現今是 21%。

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

所以，很重要的是，恐龍要能夠

在這種低氧的環境中呼吸，

in this low-oxygen environment,

not only to survive

不僅要能生存，

but to thrive and to diversify.

還要能茁壯和產生多樣性。

So, how do we know what dinosaur lungs were even like,

那麼，我們要怎麼知道 恐龍的肺部是什麼樣子，

since all that remains of a dinosaur generally is its fossilized skeleton?

畢竟恐龍留下來的部分 通常都只是骨骼的化石？

The method that we use is called "extant phylogenetic bracketing."

我們用的方法叫做 「延伸親緣包圍法」。

This is a fancy way of saying that we study the anatomy --

這是種很炫的說法，其實意思 就是我們會去研究解剖結構——

specifically in this case, the lungs and skeleton --

在這個例子中， 是研究肺部和骨骼——

of the living descendants of dinosaurs on the evolutionary tree.

從恐龍的演化樹上找出 現存的後裔來當研究對象。

So we would look at the anatomy of birds,

所以，我們會研究 鳥類的解剖結構，

who are the direct descendants of dinosaurs,

鳥類是恐龍的直屬後裔，

and we'd look at the anatomy of crocodilians,

我們會去研究鱷魚類 動物的解剖結構，

who are their closest living relatives,

牠們是恐龍最近的活親戚，

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

接著，我們會研究 蜥蜴和烏龜的解剖結構，

who we can think of like their cousins.

我們可以把牠們視為恐龍的表親。

And then we apply these anatomical data to the fossil record,

接著，我們把這些解剖學 資料套用到化石記錄上，

and then we can use that to reconstruct the lungs of dinosaurs.

然後，我們就可以依此 重新建造出恐龍的肺部。

And in this specific instance,

在這個特殊的例子中，

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

恐龍的骨骼最接近現代鳥類。

So, because dinosaurs were competing with early mammals during this time period,

因為，在這個時期， 恐龍要和早期的哺乳類競爭，

it's important to understand the basic blueprint of the mammalian lung.

很重要的是要了解 哺乳類肺部的基本藍圖。

Also, to reintroduce you to lungs in general,

此外，為了讓各位 對肺部有一般性的了解，

we will use my dog Mila of Troy,

我們要用我的狗， 特洛伊的米拉（標誌），

the face that launched a thousand treats,

牠的臉出現在一千種 市面上的零食上，

as our model.

用牠來當我們的模型。

(Laughter)

（笑聲）

This story takes place inside of a chest cavity.

這個故事發生在胸腔內。

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

請各位視覺化想像狗的胸廓。

Think about how the spinal vertebral column

想想看牠的脊柱

is completely horizontal to the ground.

完全和地面呈水平。

This is how the spinal vertebral column is going to be

在我們等下要談的所有動物身上， 脊柱都是這個樣子的，

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

whether they walked on two legs

不論是用兩隻腳或四隻腳走路。

or four legs.

Now I want you to climb inside of the imaginary ribcage and look up.

現在，請各位爬入 想像的胸廓中，向上看。

This is our thoracic ceiling.

這是胸腔的頂部。

This is where the top surface of the lungs comes into direct contact

肺部的上表面會直接接觸到

肋骨和脊椎骨的這個地方。

with the ribs and vertebrae.

This interface is where our story takes place.

我們的故事就始於這個交界面。

Now I want you to visualize the lungs of a dog.

現在，請各位視覺化想像狗的肺部。

On the outside, it's like a giant inflatable bag

它的外部就像是一個 巨大的可充氣袋子，

where all parts of the bag expand during inhalation

在吸氣時，袋子的各部分都會擴張，

and contract during exhalation.

在吐氣時會收縮。

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

袋子內部，有一連串分歧的管子，

and these tubes are called the bronchial tree.

這些管子叫做支氣管樹。

These tubes deliver the inhaled oxygen to, ultimately, the alveolus.

吸入的氧氣

最終會被這些管子送到肺泡。

They cross over a thin membrane into the bloodstream by diffusion.

它們會透過擴散的方式， 穿過薄膜進入血液中。

Now, this part is critical.

這部分十分關鍵。

The entire mammalian lung is mobile.

哺乳類的整個肺部都是移動式的。

That means it's moving during the entire respiratory process,

意思就是，在整個 呼吸過程中它都在動，

so that thin membrane, the blood-gas barrier,

因此，這片薄膜：血液－氣體屏障，

cannot be too thin or it will break.

不能太薄，不然就會破裂。

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

請記著這片血液－氣體屏障， 我們等下會再談到它。

So, you're still with me?

各位還在吧？

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

因為我們要開始談鳥類， 這部分會很讓人抓狂。

so hold on to your butts.

所以，坐穩了。

(Laughter)

（笑聲）

The bird is completely different from the mammal.

鳥類和哺乳類完全不同。

And we are going to be using birds as our model

而我們要用鳥類來當模型，

to reconstruct the lungs of dinosaurs.

重新建造出恐龍的肺部。

So in the bird,

在鳥類體內，

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

空氣會穿過肺部， 但肺部不會擴張或收縮。

The lung is immobilized,

肺部不會動，

it has the texture of a dense sponge

它的材質就像是密實的海綿，

and it's inflexible and locked into place on the top and sides by the ribcage

它沒有彈性，

且被胸廓從上方和側邊 固定在一個位置，

and on the bottom by a horizontal membrane.

底部則是被一片水平的薄膜固定。

It is then unidirectionally ventilated

接著，它會單方向通氣，

by a series of flexible, bag-like structures

方式是透過支氣管樹分枝出來的

that branch off of the bronchial tree,

一連串彈性袋狀結構，

beyond the lung itself,

這些結構在肺部外面，叫做氣囊。

and these are called air sacs.

Now, this entire extremely delicate setup is locked into place

這整個非常精緻的機構，

被一組交叉的肋骨固定住，

by a series of forked ribs

all along the thoracic ceiling.

這些肋骨全都沿著胸腔頂部排列。

Also, in many species of birds,

在許多鳥類物種當中，

extensions arise from the lung

肺部和氣囊會產生出延伸物，

and the air sacs,

they invade the skeletal tissues --

它們會入侵到骨骼組織——

usually the vertebrae, sometimes the ribs --

通常是脊椎，有時是肋骨——

and they lock the respiratory system into place.

它們會把呼吸系統固定好。

And this is called "vertebral pneumaticity."

這就叫做「脊椎氣腔」。

The forked ribs and the vertebral pneumaticity

交叉的肋骨和脊椎氣腔

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

是我們能在化石記錄中 獵尋的兩條線索，

because these two skeletal traits

因為這兩項骨骼特性

would indicate that regions of the respiratory system of dinosaurs

就代表恐龍的呼吸系統區域

are immobilized.

是不會動的。

This anchoring of the respiratory system

呼吸系統被固定住，

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

促使血液－氣體屏障演化， 變得越來越薄，

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

也就是氧氣擴散到血液中時

要穿過的那層薄膜。

The immobility permits this because a thin barrier is a weak barrier,

因為這層薄屏障並不堅固，

要系統固定不動才有可能如此，

and the weak barrier would rupture if it was actively being ventilated

如果系統會主動通氣， 這片不堅固的屏障就會破裂，

like a mammalian lung.

像在哺乳類的肺部一樣。

So why do we care about this?

所以，我們為何要在乎這點？ 這有什麼重要的？

Why does this even matter?

Oxygen more easily diffuses across a thin membrane,

氧氣比較容易透過薄膜擴散，

and a thin membrane is one way of enhancing respiration

且，

在低氧的條件下，

薄膜是強化呼吸的一種方式——

under low-oxygen conditions --

low-oxygen conditions like that of the Triassic period.

比如三疊紀時期的條件 就是低氧的條件。

So, if dinosaurs did indeed have this type of lung,

所以，如果恐龍確實有這種肺部，

they'd be better equipped to breathe than all other animals,

牠們的呼吸能力 就會比其他動物更好。

including mammals.

包括哺乳類。

So do you remember the extant phylogenetic bracket method

各位還記得延伸親緣包圍法嗎？

where we take the anatomy of modern animals,

也就是把現代動物的解剖結構

and we apply that to the fossil record?

應用到化石記錄上？

So, clue number one was the forked ribs of modern birds.

所以，第一條線索是 現代鳥類的交叉肋骨。

Well, we find that in pretty much the majority of dinosaurs.

我們在大多數的恐龍身上 都找到這條線索。

So that means that the top surface of the lungs of dinosaurs

這就表示，恐龍肺部的上表面

would be locked into place,

會被固定住，

just like modern birds.

就像現代鳥類一樣。

Clue number two is vertebral pneumaticity.

第二條線索是脊椎氣腔。

We find this in sauropod dinosaurs and theropod dinosaurs,

我們在蜥腳下目及獸腳亞目 恐龍身上都有找到，

which is the group that contains predatory dinosaurs

這些恐龍包括了掠食性恐龍，

and gave rise to modern birds.

並導致現代鳥類的出現。

And while we don't find evidence of fossilized lung tissue in dinosaurs,

雖然我們沒有找到恐龍的 肺組織化石來當作證據，

vertebral pneumaticity gives us evidence of what the lung was doing

脊椎氣腔給我們證據證明

這些動物活著的時候肺部如何運作。

during the life of these animals.

Lung tissue or air sac tissue was invading the vertebrae,

肺部組織或氣囊組織在入侵脊椎，

hollowing them out just like a modern bird,

掏空它們，就像現代鳥類一樣，

and locking regions of the respiratory system into place,

把呼吸系統區域固定住，

immobilizing them.

讓它們無法動彈。

The forked ribs

交叉的肋骨

and the vertebral pneumaticity together

再加上脊椎氣腔

were creating an immobilized, rigid framework

可以創造出不會動的堅硬框架，

that locked the respiratory system into place

把呼吸系統固定好，

that permitted the evolution of that superthin, superdelicate blood-gas barrier

因而能夠演化出超級薄、

超級細緻的血液－氣體屏障，

that we see today in modern birds.

也就是現代鳥類體內的那種。

Evidence of this straightjacketed lung in dinosaurs

證明恐龍具有被束縛的肺部，

means that they had the capability to evolve a lung

就意味著牠們有能力 可以讓肺部演化，

that would have been able to breathe

讓他們能夠在三疊紀時代的

under the hypoxic, or low-oxygen, atmosphere of the Triassic period.

低氧大氣中呼吸。

This rigid skeletal setup in dinosaurs would have given them

恐龍體內這種堅硬的骨骼結構

讓牠們在適應上比其他動物

a significant adaptive advantage over other animals, particularly mammals,

（特別是哺乳類）有明顯優勢，

whose flexible lung couldn't have adapted

其他動物的肺部有彈性，

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

無法適應三疊紀時代的低氧大氣。

This anatomy may have been the secret weapon of dinosaurs

這項解剖結構可能是 恐龍的秘密武器，

that gave them that advantage over other animals.

讓牠們比其他動物更有優勢。

And this gives us an excellent launchpad

這也讓我們有很好的基礎，

to start testing the hypotheses of dinosaurian diversification.

可以開始測試恐龍多樣化的假設。

This is the story of the dinosaurs' beginning,

這個故事講的是恐龍的起源，

and it's just the beginning of the story of our research into this subject.

就我們對這個主題的研究而言， 這個故事只是個開端而已。

Thank you.

謝謝。

(Applause)

（掌聲）