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为什么现代的动物都不像恐龙那么大?

Why Aren't Modern Animals As Large As Dinosaurs?

嘿 进化之神 我们为何没有巨型宠物?
Hey, evolution, why aren’t giant pets a thing yet, huh?
恐龙能长到房子大小 为何我不能有这样
If dinosaurs grew enough to fill a whole room, why can’t I have a big red dog the size
的宠物狗呢?
of a house?
大家好 我是DNews的莉赛特
Hey everyone, Lissate here for DNews.
我们对恐龙的主要印象是他们巨大的体型
Part of what captures our imagination about dinosaurs is just how huge some of them were.
美国自然历史博物馆有一座巨型雷龙化石
The American Museum of Natural History has a cast of a titanosaur that’s so big it
体型大到恐龙展厅无法容下
doesn’t completely fit in the dinosaur wing.
这个长达37米的庞然大物向着电梯伸展出去
The 37 meter (122 foot) long behemoth’s head has to poke out towards the elevators.
它的有些骨头甚至比人还大
It’s got individual bones bigger than people.
这一类的恐龙普遍被称为“巨无霸”
The very name of the group of dinosaurs it belongs to has the word TITAN in it.
当开始思考这些灭绝生物的体型时 你已
But when you start to consider the size of some of these extinct species, it can make
是个猛禽哲人了
you a philoso-raptor.
“为何如今的陆地动物没有这么大呢?”
“Why isn’t any land animal this huge today?” you may wonder…
你不是唯一的疑问者 很幸运
Well you’re not the only one. Lucky for us
古生物学家也一直在探讨这个问题
Paleontologists have been debating the same question, and they’ve come up with a number
并提出许多不同的证据来解释 相比古代生物
of different factors that could explain why some giant reptiles of yesteryear dwarf modern
为何现代生物如此矮小
land creatures.
你必须知道恐龙生活在非常久远的年代
It’s important to keep in mind that dinosaurs lived a long time ago.
没有疑问吧?
No doubt, right?
但你也许不知道的是 恐龙灭绝前
But what you may not realize is, before the dinosaurs were wiped out they were living
当时的地球完全不同于如今的样子
on a completely different kind of earth than we live in today.
恐龙在距今2亿3千年前登上历史舞台
Dinosaurs actually started coming onto the scene about 230 million years before present.
当时 空气中二氧化碳的浓度很高
During their existence, CO2 levels were all over the place.
估测各不相同 大气中二氧化碳含量
Estimates vary but (for some stretches) there could have been 3 to 5 times as much carbon
可能是如今的三到五倍左右
dioxide in the atmosphere as there is today.
也就是说整个地球 即使是高纬地区都非常热
This means the world as a whole was a lot hotter even if at higher latitudes
而且 在中生代初期 大陆还是一整块的
And, because at the beginning of the Mesozoic Era, all land was clumped together in Pangea,
所以海洋并未对超级大陆起到降温作用
the ocean didn’t have as much of a cooling effect on the supercontinent.
这会使地球更适宜巨型冷血爬行动物生存
This would make the planet a more hospitable place for, I don’t know, giant cold-blooded
因为它们不必消耗热量来保持体温
reptiles that wouldn’t have to waste energy maintaining body heat.
看 全球变暖的又一害处
See… another reason to worry about global warming.
别坐车啦 改骑单车吧 除非你想在后视镜里看到霸王龙
Get out of that SUV and onto a bike unless you want to see T-rexes in your sideview mirror.
不过学术界对大气成分影响恐龙体型
It may comfort you to know that paleontologists aren’t all in agreement on the exact amount
的观点还未统一意见
the atmosphere’s impacted dinosaur size.
它也可能完全没有影响 我们仍未确认
It could have had no effect at all, and whether or not dinosaurs were all cold-blooded
所有的恐龙都是冷血动物
is even up for debate.
富足的食物也可能使它们的体型巨大
Their size could have also been driven by an abundance of food.
二氧化碳意味着可能有更多的植被
All that CO2 meant there was likely more vegetation.
长得更加茂密 食草动物也更加繁多
If there’s plentiful vegetation, then large herbivores can thrive.
恐龙巨大的体型使它们有更长的肠道
They’d actually benefit from being bigger because longer intestines would be better
来消化植物物质并吸收营养
at breaking down plant matter and extracting its nutrients.
然后 他们可以花更少的时间咀嚼 花更多的时间大快朵颐
Then they could spend less time chewing, and more time stuffing green down their giant gullets
如果恐龙没有随着食草动物体型变大
Also if the herbivores grew larger, then they were harder for predators to take down.
消化会变得困难
Until the predators got bigger.
因此食草动物体型变大
Then the herbivores would get bigger.
食肉动物就会随之变大
Then the predators would get bigger again.
结果可想而知 这并不是好事
You see where this is going and it’s not good
重力等物理因素会导致体型增长有上限
But there is an upper limit to size, because of physical constraints — like gravity.
鲸体型大的原因之一是海洋能承受其重量
Part of the reason whales can get so huge is because the ocean supports their weight.
在没有这种生活条件下(在重力作用下)
On land, a similar sized animal would crush itself
和鲸体型相差不大的陆生动物可能会将自己压死
without some clever life hacks.
与哺乳动物相比 像蜥脚类巨型恐龙有更轻质的骨骼
Huge dinosaurs like sauropods had lightweight bones compared to mammals
因为它们的骨骼是中空的
because theirs were hollow.
而且恐龙比哺乳动物体型更易变大
Dinosaurs also had another advantage over mammals, when it comes to living large
它们产卵
They laid eggs.
卵生相比胎生能使它们更易
If they had to give birth to live young, it would be much harder for them to have large
繁衍后代
offspring quickly.
比如 大象妊娠期长达22个月 由于
For instance, elephants have 22 month gestation periods… they can’t breed very quickly because
需要大量资源和宽的产道 不能快速繁殖
live-birth is so resource intensive — and it requires a large birth canal.
有趣的是 中空骨头和卵生的特性让恐龙
Interestingly, these traits of hollow bones and egg-laying have come in handy in a very
能游刃有余的生存 甚至进化出了会飞的后代
different way today: they make it possible for the descendants of dinosaurs to fly.
没错 就是鸟
That’s right, I’m talking about birds.
恐龙体型巨大的原因仍在探讨中 希望我们会有更多的发现
Why they were so big is still a matter of debate, and hopefully we’ll find more research out there
目前生物学家试图通过对众多残存的化石碎片进行研究
But at the moment they’re trying to put together a hundred-million-year-old
来破解一亿年来的谜团
puzzle with a lot of missing pieces.
想要了解更多有关现存的咸水生物的讯息
Want to learn more on huge salt water creatures that are alive today
不要错过动物星球频道每周四的新节目
Don’t miss new episodes of River Monsters every Thursday at 9/8c on Animal Planet!
事实上 恐龙和鸟类相同
Seriously, though, dinosaurs equal birds.
这个视频讲述凶猛的恐龙到被毛的鸟类完整缓慢进化过程
Here’s a video all about their gradual shift from ferocious predators to feathered peckers.
上个月发表在《科学》杂志上的另一项研究发现
Separate research also published in Science last month theorizes that
所有恐龙都有羽毛
all dinosaurs had feathers.
有些更原始的羽毛像毛发或刚毛
Some were more primitive like hairs or bristles,
而另一些则像现代鸟类一样柔软或毛茸茸的
while others were soft and downy like modern Birds
所以你是想要恐龙灭绝
So are you glad giant reptiles no longer run amok,
还是想拥有一个猛禽宠物呢?
or would you want a pet raptor?
在评论中分享你的想法 并订阅DNews
Share your thoughts in the comments and remember to subscribe to DNews,
这样你就不会错过任何精彩内容
so you never miss an episode.
感谢你们的收看
Thanks for watching, guys.

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视频概述

巨型恐龙的成因

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收集自网络

翻译译者

陌桑成海‮脸小的你了亲并‭

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视频来源

https://www.youtube.com/watch?v=ZsQ7Cbi5QWY

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