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Hey, evolution, why aren't giant pets a thing yet, huh?
嘿，进化，为什么巨型宠物还没出现？啊？
If dinosaurs grew enough to fill a whole room, why can’t I have a big red dog the size of a house?
如果恐龙能长得塞满整个房间那么大，那我为什么不能养一只一栋房子那么大的大红狗呢？
Hey everyone, Lissette here for DNews.
大家好，我是Lissette，欢迎收看本期的DNews视频。
Part of what captures our imagination about dinosaurs is just how huge some of them were.
恐龙之所以能让我们遐想连篇，部分原因在于他们的个头实在是太大了。
The American Museum of Natural History has a cast of a titanosaur that’s so big it doesn’t completely fit in the dinosaur wing.
美国自然历史博物馆里就有一只大到展厅放都放不下的泰坦龙。
The 37 meter (122 foot) long behemoth’s head has to poke out towards the elevators.
这个身长37米(122英尺)的庞然大物的头都伸到电梯里了。
It’s got individual bones bigger than people.
它的骨头比人都大。
The very name of the group of dinosaurs it belongs to has the word TITAN in it.
正因为如此，它所属的恐龙群的名字中才有了“泰坦”这个词。
But when you start to consider the size of some of these extinct species, it can make you a philoso-raptor.
不过，当你开始思考这些已经灭绝的物种的体型大小时，你就在朝猛禽哲人的方向发展了。
“Why isn’t any land animal this huge today?” You may wonder.
你可能会想，“当今世界为什么就没有这么大的陆地动物？”
Well you’re not the only one.
事实上，这么想的并不止你一个。
Lucky for us, paleontologists have been debating the same question, and they’ve come up with a number of different factors
算我们走运，古生物学家也一直在探讨这个问题，他们还提出了很多种观点，
that could explain why some giant reptiles of yesteryear dwarf modern land creatures.
来解释为什么现代的陆地生物跟古代的某些巨型生物比起来是那么的矮小。
It’s important to keep in mind that dinosaurs lived a long time ago.
很重要的一点是，恐龙生活在非常久远的年代。
No duh, right?
没毛病，对吧？
But what you may not realize is, before the dinosaurs were wiped out,
但你可能不知道的是，在恐龙灭绝之前，
they were living on a completely different kind of earth than we live in today.
它们生活的年代的地球和我们当今的地球完全是两个模样。
Dinosaurs actually started coming onto the scene about 230 million years before present.
事实上，恐龙是在距今2亿3千年左右登上历史舞台的。
During their existence, CO2 levels were all over the place.
那个年代的地球二氧化碳浓度非常高。
Estimates vary but (for some stretches) there could have been 3 to 5 times as much carbon dioxide in the atmosphere as there is today.
不同研究估计出来的数值各不相同，但(在某些地方)当时大气中的二氧化碳含量可能高达今天的3~5倍。
This means the world, on the whole, was a lot hotter - even up at higher latitudes.
这就意味着，当时的整个地球，即使是高纬度地区，都比现在热得多。
And, because at the beginning of the Mesozoic Era, all land was clumped together in Pangea,
而且，因为中生代初期大陆还是一整块，
the ocean didn’t have as much of a cooling effect on the supercontinent.
海洋对这块超级大陆的降温作用也没有那么明显。
This would make the planet a more hospitable place for,
这就使得地球更适宜，我也不知道怎么说，
I don’t know, giant cold-blooded reptiles that wouldn’t have to waste energy maintaining body heat.
体型巨大的冷血爬行动物生存了？因为它们不需要浪费能量维持体温嘛。
See...another reason to worry about global warming.
看见没...全球变暖的又一害处啊。
Get out of that SUV and onto a bike unless you want to see T-rexes in your sideview mirror.
这个时候你就别坐在车里了，改骑单车吧，除非你想从后视镜里看霸王龙。
It may comfort you to know that paleontologists aren’t all in agreement on the exact amount the atmosphere’s impacted dinosaur size.
不过，关于大气成分对恐龙体型大小的影响究竟有多大，古生物学家们并没有达成一致看法。
It could have had no effect at all, and whether or not dinosaurs were all cold-blooded, is even up for debate.
有可能一点儿影响也没有，而且，恐龙是否都是冷血动物也还没有定论。
Their size could have also been driven by an abundance of food.
它们的体型之所以那么大还可能是因为食物太富足造成的。
All that CO2 meant there was likely more vegetation.
那么高的二氧化碳浓度意味着那时候的植被可能也比现在多。
If there’s plentiful vegetation, then large herbivores can thrive.
如果有丰富的植被，那大型食草动物就能生生不息地繁殖了。
They’d actually benefit from being bigger because longer intestines would be better at breaking down plant matter and extracting its nutrients.
事实上，体型大还有一个好处，肠道长有利于分解吃进去的植物，吸收营养。
Then...they could spend less time chewing, and more time stuffing green down their giant gullets.
不仅如此，肠道长了，就不用花那么多时间咀嚼了，也就有更多的时间大快朵颐了。
Also if the herbivores grew larger, then they were harder for predators to take down.
此外，如果草食性动物体型变大了，它们的天敌就很难吃下它们。
Until the predators got bigger.
直到它们自己也变得更加庞大。
Then the herbivores would get bigger.
它们变大了草食性动物也会继续变大。
Then the predators would get bigger again.
然后天敌再继续变大。
You see this is where I'm going and it's not good.
结果就可想而知了，但这并不是一件好事。
But there is an upper limit to size, because of physical constraints -- like gravity.
体型大小也是有上限的，因为有物理限制——比如重力。
Part of the reason whales can get so huge is because the ocean supports their weight.
鲸能够长特别大一定程度上是因为有海洋托着它们的体重。
On land, a similar sized animal would crush itself without some clever life hacks.
如果是在陆地上，同样大小的动物，如果没有一些生活绝招的话，可能会将自己给压死。
Huge dinosaurs like sauropods had lightweight bones compared to mammals because theirs were hollow.
和哺乳动物相比，蜥脚类恐龙等体型较大的恐龙的骨骼算轻的了，因为它们的骨头都是空心的。
Dinosaurs also had another advantage over mammals, when it comes to living large: they laid eggs.
说到体型大，比起哺乳动物，恐龙还有另外一个优势：它们是蛋生生物。
If they had to give birth to live young, it would be much harder for them to have large offspring quickly.
如果它们是胎生动物，势必很难快速繁衍。
For instance, elephants have 22 month gestation periods…
打个比方，大象的妊娠期为22个月。
they can't breed very quickly
它们就没办法快速繁衍，
because live-birth is so resource intensive and it requires a large birth canal.
因为胎生需要大量的资源，还需要母体有较宽的产道。
Interestingly, these traits of hollow bones and egg-laying have come in handy in a very different way today:
有趣的是，站在今天来看，中空骨骼，卵生这些特征都以不同的方式派上用场了：
they make it possible for the descendants of dinosaurs to fly.
正是这些特征让恐龙的后代有了飞翔的潜能。
That’s right, I’m talking ‘bout birds.
没错，我说的就是鸟。
Look, why they were so big is still a matter of debate, and hopefully we'll find more research out there…
恐龙为什么那么大这个问题至今仍没有定论，顺利的话，我们能得出更多的发现，
but at the moment they’re trying to put together a hundred-million-year-old puzzle with a lot of missing pieces.
不过，就目前来看，科学家们的研究依然还停留在拼凑一个亿万年前的，到处都是残缺的拼图的阶段。
Wanna learn more on huge salt water creatures that are alive today,
想了解更多有关现存咸水生物的信息？
don’t miss new episodes of River Monsters, every Thursday at 9/8c on Animal Planet!
那就不要错过《动物星球》每周四9/8C播出的新一集《河里的怪兽》！
Seriously, though, dinosaurs equal birds.
不过，说真的，恐龙和鸟类是可以划等号的。
Here’s a video all about their gradual shift from ferocious predators to feathered peckers.
接下来的片段就展示了它们从凶猛的捕食者逐渐变成有羽毛的小鸟的过程。
A seperate research also published on Science last month theorizes that all dinosaurs have feathers.
上个月同样发表在《科学》杂志上的另一研究推断称，所有的恐龙都有羽毛。
Some were more primitive like hairs or bristles while others were soft and dainty like modern birds.
有一些的羽毛相对比较原始，跟毛发或鬃毛差不多，另外一些的羽毛则比较柔软精致，跟现代的鸟类的羽毛差不多。
So are you glad giant reptiles no longer run amok, or would you want a pet raptor?
那么问题来了，你是对现在已经没有巨型爬行动物横冲直撞感到高兴呢？还是会想养一只猛禽当宠物呢？
Share your thoughts and comments and remember to subscribe to Dnews so you never miss an episode, thanks for watching guys.
快来跟我们分享你的想法和评论吧，还有，记得订阅，这样你就能一集不落地收看我们的节目啦。感谢大家的收看。
