The fact that these wildly different creatures roamed the earth millions of years ago is not only awe-inspiring, but terrifying.

這些數百萬年前在地球上生活著，與我們截然不同的生物們不但讓人驚嘆，更讓人害怕。

One thing that has stood out to paleontologists is the seemingly odd rule that carnivorous dinosaurs are either really huge, like the Tyrannosaurus Rex, or really small like Compsognathus.

古生物學家們在研究肉食性恐龍時發現了一條看似有些奇怪的規則，那就是肉食恐龍的體型要不就是像暴龍那樣非常巨大，要不就是像細頸龍那樣非常的小。

You know those creepy ones from Jurassic Park that look all cute and cuddly at first - and then they go nuts.

細頸龍就是《侏儸紀公園》裡面出現過，一開始看起來可愛又黏人－然後就突然發狂了的那種龍。

Stay away.

遠離牠們。

Take a look at these two diagrams.

看一下這兩張圖。

First looking at modern day carnivorous land mammals from Kruger National Park in South Africa.

我們先看看來自南非克魯格國家公園的現代肉食性陸生哺乳動物。

From lions and leopards all the way down to things like the small-spotted genet, you can see in this ecosystem the size of these animals is distributed across a gradient pretty evenly.

從獅子、獵豹在一路到小斑獛，你可以看到在這個生態系統中，動物的大小在每一個梯度上的分佈是相當均勻的。

And this is true of other geographies as well.

而世界上其他地方也是如此。

They all fill their own niche with their own prey targets.

牠們都有著自己的獵食目標。

But now take a look at the scale of these carnivorous dinosaurs all found in the dinosaur park formation in Alberta, which have been scaled to match the largest mammal above and you'll quickly notice a massive gap in the middle.

但接下來我們再來看到這些肉食性恐龍的體型，它們都是在加拿大亞伯達省的恐龍公園地層中發現的。當我們把牠們的比例與上面最大的哺乳動物相匹配時，你很快就會注意到中間的巨大差距。

For perspective, if the modern carnivores were similarly distributed, there would be no carnivores between the size of an African lion and a bat eared fox.

從這個角度來看，如果現代肉食性動物的分佈與恐龍相似，世界上就不會有大小在非洲獅和蝠耳狐大小之間的食肉動物。

On top of all this, our understanding of dinosaurs is that there were way more large carnivorous species than there were small, which is the opposite of what we see today in land animals.

除此之外，我們還知道大型肉食性恐龍的種類遠比小型的還多，而這與我們現今在陸上動物中所能觀察到的情況相反。

It tends to be lots of diversity in small organisms, lower diversity in medium sized organism, and then very low diversity in large organisms, which makes sense based on Energetics.

往往會是小型生物體有著高多樣性，中型生物體的多樣性較低，而大型生物體的多樣性則非常低。這在能量學上是說得通的。

So the smaller you are, the less food you need, and the more you can kind of partition your ecosystem.

因為體型越小所需的食物越少，整個生態系統便更能被瓜分出不同部分。

Dinosaur is the exact opposite.

但恐龍的狀況越完全相反。

When we look at them in a global scale, most of them are big.

以全球的規模廣範圍來看，牠們大多都很龐大。

To understand this phenomenon, we first have to look at the fossil records.

要深入瞭解這個現象，我們得先看看化石紀錄。

Dinosaurs weren't super diverse. Compared to the tens of thousands of mammals and birds species we see today, there are maybe only around 1500 known dinosaur species, and of these species a lot more were over 1000 kg than under 60 kg.

恐龍的物種多樣性並不高。與現今世界上數萬種哺乳類與鳥類相比，我們已知的恐龍物種只有 1500 種，而超過 1000 公斤的物種要比小於 60 公斤的物種要來得多非常多。

But least of all very few carnivorous dinosaurs existed between those two sizes, especially around the Cretaceous period, which is 145.5 To 65 million years ago.

但最重要的是，很少有肉食性恐龍介於這兩種體型之間，特別是在白堊紀，也就是1.455 億年到 6500 萬年前的時候。

Turns out there's something really unique about massive dinosaurs: their babies are small.

我們能發現這些巨大的恐龍都有個共通的特點：牠們的恐龍寶寶體型很小。

Now that may not surprise you; lots of babies are small. But it has more to do with the fact that their egg laying creatures.

你可能不會為此感到驚訝，畢竟哪有寶寶體型不小的呢。但這其實與牠們是卵生動物更有關聯。

Oviparous animals are those that lay their eggs with little to no embryonic development inside the mother.

卵生動物就是生育時母體內幾乎沒有或沒有胚胎發育的情況下，進行生育的物種。

And so dinosaurs started out weighing no more than 15 kg, but a T-Rex adult can grow to be 7000 kg.

所以恐龍出生時只有不到 15 公斤，但成年的暴龍能成長到 7000 公斤。

Compare that with a larger animal today, like a giraffe, which weighs around 68 kg when it's born, and ends up around 800 kg as an adult.

與如今的大型動物相比，像是長頸鹿出生時體重約為 68公斤，成年則能成長為 800 公斤。

An egg can only be about the size of a football because of how gas is exchanged through a shell.

由於氣體通過蛋殼換氣的機制限制，一個雞蛋只能有橄欖球般的大小。

Even a sauropod that is getting up into the 80 ton range and is just immensely huge, are still being born like your average border collie size.

即使是能成長到 80 噸重，極為龐大的蜥腳類恐龍，在出生時也和邊境牧羊犬差不多大小而已。

So how does that impact the size of other dinosaurs?

那麼這對其他恐龍的大小有什麼影響呢？

The theory is that these baby T-Rexes would have had an almost entirely different diet than their parents because they were physically so different.

該理論認為，由於生理條件截然不同，這些暴龍寶寶的飲食與它們的父母幾乎完全不一樣。

And because of this, as they became teenagers, they would actually be competing for resources with other medium sized dinosaurs, a niche that would have contained different foods than what an adult T-Rex was eating.

正因如此，當他們成為青少年時，他們實際上會與其他中等大小的恐龍競爭資源，而他們所吃的食物與成年暴龍是不同的。

For example, a young T-Rex likely couldn't take on a Triceratops because they were much more slender than adults, only turning into bone crushers after a teenage growth spurt.

例如，年幼的暴龍很可能無法與三角龍對抗，因為牠們比成熟個體來得要瘦弱得多，要成長到十幾歲的時候才會變成凶狠的碎骨者。

And so they instead would go for something smaller.

因此牠們便會去找一些更小的獵物。

And it looks like they simply just out competed other medium-sized dinosaurs.

而牠們似乎就這樣在競爭中勝過了其他中等大小的恐龍。

Of course, those teenagers would eventually grow up into adults T-Rexes, but their population as teenagers would have had a massive impact on other dinosaur communities and the ecosystem at large.

當然，這些青少年最終會成長為成年暴龍，但它們在青少年時的數量足以對其他恐龍族群和整個生態系統產生巨大影響。

So then why don't we see this gap in herbivores?

那麼，為什麼我們在草食性恐龍身上沒有看到這種差距？

They lay eggs to and grow to even more massive sizes.

它們也會產卵，而且甚至會成長得更龐大。

It's more likely that they're young simply ate the same foliage as the parents.

較為可能的原因是，牠們的幼崽和父母一樣都只吃葉子。

After all, you don't have to put up too much of a fight to take down a leaf.

畢竟，只是咬下一片樹葉並不需要花費多大力氣。

Though I will say rose thorns, terrifying.

但玫瑰刺另當別論，那很可怕的。

Don't want to be near them. Don't want to get in a fight.

別靠近他們。別徒生爭端。

Either way for herbivores, the food barrier just isn't as high.

對於食草恐龍來說，進食障礙並沒有肉食性恐龍來得高。

Herbivores have their... have the opportunity to partition their resources and their ecosystem vertically so they can move up and down in a tree.

食草恐龍有... 有機會垂直地劃分牠們的資源和生態系統，讓牠們以樹的上與下來做區分。

So a big tall sauropod can be eating at the tops of the trees, while a teeny tiny baby sauropod can be eating at the bottom of the tree.

高大的蜥腳類恐龍可以吃樹頂上的葉子，而十幾公分的迷你蜥腳類恐龍寶寶則可以吃在樹底的植物。

So they're not necessarily resource-limited in the way that carnivores are resource-limited, because a carnivore, they're going to have to be competing with one another.

因此牠們不一定會像食肉動物一樣資源受限，因為牠們不像那樣食肉動物必須相互競爭。

That explains in part why we don't see it in herbivores.

這在一定程度上解釋了為什麼我們沒有在食草恐龍身上看到這種狀況。

Because of this, some even suggest that juvenile mega theropods, like the T-Rexes, could be considered their own species in an ecological type of way.

有藉於此，有些人甚至認為像暴龍這樣的幼年巨型獸腳亞目，在生物分類可以被單獨劃分為為專屬的物種。

Obviously they're technically the same species, but because their diets and impact on the ecosystem is so different than an adult, in that way, they're almost like their own species.

牠們顯然在技術上仍是同一物種，但由於牠們的飲食和對生態系統的影響與成年人如此不同，使得牠們幾乎就像是一個分別的獨立物種。

In fact, when researchers added juveniles as their own species into their models, the gap in sizes suddenly disappears,

事實上，當研究人員將幼龍作為獨立的物種加入到他們的模型中時，尺寸上的差距突然消失了，

which helps further support the theory that the juveniles of mega theropods were actually out-competing other medium sized dinosaurs, ultimately leaving a gap in the diversity of species.

這更進一步支持了這樣的理論，即獸腳亞目的幼龍實際上是在與其他中等尺寸的恐龍競爭，最終在物種的多樣性上留下缺口。

It wasn't that there were no medium -sized dinosaurs per se, it was that the big guys teenagers were simply taking their place.

這並不是說世上沒有中等大小的恐龍，而是那些大傢伙的青少年們取代了牠們的位置。

Speaking of huge, I want to give a huge thank you to today's sponsor: Skillshare, who's giving a free trial of their premium membership to the 1st 1000 people who click the link in our description.

說到巨大，我想對今天的贊助商：Skillshare 致上大大的謝意。Skillshare 將會給點擊影片下方說明欄中連結的前 1000 名觀眾，免費體驗尊榮會員的機會。

Go quick click it.

快去點擊它吧。

Skillshare is an amazing online community where you can be inspired to learn something new from your own home.

Skillshare 是一個超讚的在線社群，在那裡你可以得到啟發，在自己的家裡學習新的東西。

It's truly become a vital part of my life.

而它確實已經成為了我生活中的一個重要部分。

They have so many different classes of all different topics, and I highly highly recommend it.

他們有非常多不同主題的課程，我非常、非常的推薦。

One of our favorite creators, Marques Brownlee or MKBHD, just released a class called: "YouTube Success: Script, Shoot and Edit with MKBHD", which is a deep inside look at the creator process with one of the best creators on this platform.

我們最愛的創作者之一：Marques Brownlee，也被叫做 MKBHD，剛剛發佈了一個名為「YouTube 成功之路：與 MKBHD 一起寫腳本、拍攝和剪輯」的課程，內容將會深入探索在這個平台上最佳創作者之一的創作過程。

Also one of the nicest, truly, one of the best.

他同時也是人最好的創作者，真的，他真的是最棒的。

I 100% recommend that class, but there is such a huge variety of subject matters, from lifestyle, art to web design.

我百分之百推薦這個課程，不過上面還有許多包含了生活、藝術到網頁設計等不同主題的課程。

Their platform is dedicated learning, so there's no ads, they're also always launching new premium classes.

他們的平臺專門供用學習使用，所以沒有任何廣告，而他們也一直在推出新的高級課程。

It's definitely worth your money.

這絕對物超所值。

Again, the 1st 1000 people who click the link in our description will get a free trial of premium membership.

再次提醒，點擊我們影片資訊欄中連結的前 1000 人將獲得高級會員的免費試用機會。

You checking out and supporting our sponsors actually is a great way to help support our show, and allow us to keep making videos.

查看並支持我們的贊助商，實際上也是支持我們的節目，並使我們能夠繼續製作影片的好方法。

Thanks again for watching.

再次感謝你的收看。

Make sure you like the video, subscribe and we'll see you next time for some more science. Peace!

記得在影片下方按讚和訂閱，下次再為你提供更多的科學新知。掰！