象鸟: 重量堪比汽车的鸟界巨人

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象鸟: 重量堪比汽车的鸟界巨人(上)
For people who've never heard of an elephant bird, what do they need to know?
对于那些从未听说过象鸟的人来说，他们需要了解什么呢?
I think, first off, the size. They are colossal.
我想，首先是大小。它们体型庞大。
I'm Flora Lichtman, with Scientific American's Science, Quickly, and this is Episode Two of my homage to Earth's real big birds.
我是《科学美国人》“科学快播”栏目的弗洛拉·里奇曼，这是我向地球大型鸟类致敬的第二集。
Last episode, we talked about the biggest bird to fly.
上一集，我们讨论了最大的飞鸟。
Today we're homing in on the heaviest bird to set its scaly foot down on planet Earth: the elephant bird.
今天我们要关注的是将其布满鳞片的爪子踩在地球上的最重的鸟:象鸟。
They are outstanding.
它们很显眼。
This is elephant bird expert and paleontologist James Hansford …
这是象鸟专家詹姆斯·汉斯福德，他也是古生物学家……
Just absolute titans of the bird world.
绝对是鸟类世界的巨人。
Elephant birds lived in Madagascar. They seem to have been mostly herbivorous. None of them flew.
象鸟生活在马达加斯加。它们似乎主要以食草为生。它们都不会飞。
There were a number of different species that ranged from the size of an ostrich to the size of a smart car.
象鸟有许多不同的种类，体型从鸵鸟大小到智能汽车大小不等。
The biggest I measured for any of the elephant birds was somewhere around 1,900 pounds.
我测量到的最大的象鸟大约重1900磅。
My god, I'm having a hard time really even picturing that.
我的天啊，我都很难想象。
Yeah. How do you even picture it? Well, when I measured the femur around, it was 30 centimeters, over a foot in circumference. So that is ginormous.
是的。你怎么会想象得到呢? 嗯，当我测量其股骨时，它的周长为30厘米，超过一英尺。巨大无比。
Oh my god. The circumference of the femur is over a foot.
我的天啊。股骨周长超过一英尺。
Yeah.
是的。
Shut the cluck up.
不要大惊小怪啦。
These behemoths appeared 30 million years ago, and they stuck around a long time.
这些庞然大物出现在3000万年前，并且存在了很长时间。
They were alive up until 1,000 years ago, but we know so much less about them than, say, Tyrannosaurus rex.
直到1000年前，它们都一直活着，但我们对它们的了解远不如霸王龙多。
There are all these questions because there are very large gaps in the fossil record.
有这么多疑问，是因为化石记录中存在很大的空白。
That's paleogeneticist Alicia Grealy.
这是古遗传学家艾丽西亚·格雷利所言。
She worked with James and other colleagues to answer some basic questions about elephant birds, such as: Who are they related to? How did they evolve? Who made up the group?
她与詹姆斯和其他同事一起回答了一些关于象鸟的基本问题，比如: 它们和谁有亲缘关系? 它们是如何进化的? 谁组成了这个鸟群?
There's just been a lot of debate throughout history about how many species there were.
历史上有很多关于象鸟有多少种类的争论。
Scientists have debated the elephant birds family tree since their discovery in the 1800s.
自从19世纪发现象鸟族谱以来，科学家们就一直在争论。
Of particular interest are the most elephantine members of the elephant bird herd ...
尤为吸引关注的是，象鸟群中最庞大的成员……
Like the one with the giant leg bones that James mentioned.
就像詹姆斯提到的那个有着巨大腿骨的象鸟。
For a long time, the biggest specimens had been classified as jumbo members of a species known as Aepyornis maximus.
在很长一段时间里，这个最大的象鸟标本被归为一种叫做马氏象鸟的巨型成员。
But they are hundreds of pounds heavier than the other Aepyornis maximus specimens-and their bones look kinda different, too.
但是它们比其他的马氏象鸟标本重数百磅——而且它们的骨头看起来也有点不同。
And a few years ago there was a suggestion that these largest bones were so big that they must have belonged to a different species.
几年前，有人提出，这些最大的骨头太大了，它们一定属于其他不同的物种。

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象鸟: 重量堪比汽车的鸟界巨人(中)
Alicia wanted to investigate this. And as a paleogeneticist, she thought ancient DNA could help. The challenge was that DNA degrades fast in tropical environments.
艾丽西娅想对此进行调查。作为一名古遗传学家，她认为古代DNA(脱氧核糖核酸)可以提供帮助。而挑战在于DNA在热带环境中降解得很快。
Exactly, because you've got the combined effects of, you know, water damage and erosion and UV that-all of these things degrade DNA.
没错，因为这是水损害、水蚀和紫外线的综合作用，所有这些都会降解DNA。
The capacity to get genetic material, that stuff in Madagascar is really hard. I liken it to getting blood from a stone.
在马达加斯加，获得遗传物质的能力是非常困难的。我将其比作从石头里榨血，极其艰难。
But Alicia had an idea. She wondered if they could crack this big bird mystery using eggs.
但艾丽西娅有个主意。她琢磨着他们是否可以用鸟蛋来解开这个巨型鸟类的谜题。
Eggshell preserves the DNA remarkably well.
蛋壳能很好地保存DNA。
And there's a lot of eggshell to pick from. These elephant bird eggs were huge.
有很多蛋壳可供挑选。这些象鸟蛋很大。
They were about 150 times the size of a chicken egg. And that's larger than any dinosaur egg.
它们的大小约是鸡蛋的150倍，比任何恐龙蛋都大。
If you clutched one in your hands, it would be heavier than a bowling ball, with the shell as thick as a dinner plate.
如果你抓一个在手里，你会发现它比保龄球还重，它的壳和餐盘一样厚。
Yeah, they were about 10 kilos..., which is about 22 pounds....
是的，鸟蛋大概有10公斤重……，大约22镑重....
And unlike elephant bird bones, the eggs are easy to find.
与象鸟的骨头不同，蛋反而很容易找到。
Alicia says that if yo u go to the beach where she worked in the southwest of the country, you'll be walking on eggshells.
艾丽西娅表示，如果你前往她在该国西南部工作的海滩，你会在蛋壳上行走。
They're just scattered absolutely everywhere. One person described it as paved with eggshell.
蛋壳分布在各处。有人形容那片海滩是用蛋壳铺成的。
But if collecting the eggs was over-easy, getting DNA out of them wasn't.
如果说收集鸟蛋太容易了，那么，从中提取DNA却并不容易。
DNA can be scrambled in beach-fried eggs. So the team looked for shells buried in dig sites and dunes.
DNA可以用沙滩煎蛋炒制。因此，该团队寻找埋在挖掘场和沙丘中的蛋壳。
Then Alicia took each shell, cleaned it and ground it into a powder.
艾丽西娅捡起每个蛋壳，清洗干净，将其磨成粉末。
From that egg dust, mind-bogglingly, she pulled out pieces of DNA from birds that had been dead for 1,000 years.
令人难以置信的是，她从那些蛋壳粉末中提取出了已经灭绝1000年的鸟类的DNA片段。
It's mind-boggling to me as well, actually.
事实上，这对我来说也难以置信。
And she used that DNA to try to figure out if those extra, extra-large elephant birds were their own species or not.
她利用这些DNA试图弄清楚那些超大型号的象鸟是否属于这个物种。
The DNA evidence from the eggshell suggests that there wasn't two different species living in this area.
蛋壳上提取的DNA证据表明，这个地区并不存在两个不同的物种。
Basically, all of the eggshell is genetically identical.
基本上，所有蛋壳的基因都完全相同。
So if we were expecting that the largest elephant birds were a different species, then we would have seen some genetic difference in the eggshell, but we don't see that.
如果我们料想最大的象鸟属于不同的物种，那么，我们就会在蛋壳上发现一些基因差异，但我们并没有发现不同。
So what explains the XXL bones? One possibility: big mamas.
那么如何解释超大型号的骨骼呢? 一种可能是: 大骨骼的鸟妈妈。
The very big elephant birds were females, and the slightly smaller ones were the males, we think.
我们认为，非常庞大的是雌性象鸟，稍微小一点的是雄性象鸟。
Mini-er males aren't uncommon in birds because lady birds have to produce eggs, and that takes a lot out of them, literally.
雄鸟体型偏小在鸟类中并不罕见，因为雌鸟必须产卵，这确实会消耗掉很多。
Birds make eggshells from materials from inside their hollow bones.
雌鸟产卵以中空骨头里的物质为材料。
I mentioned that these thigh bones were 30 centimeters, a foot in circumference.
我提到过，这些大腿骨的周长是30厘米，也就是一英尺。
And one of the reasons for that is that the females would have stored materials within those in order to make the eggs.
雌鸟体型偏大的一个原因是，雌鸟会在骨头里面储存物质以便产卵。
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象鸟: 重量堪比汽车的鸟界巨人(下)
But that wasn't the only "aha" that plopped out of the cracked eggs.
但这并不是破壳而出的唯一发现。
Eggshells also tell us something about how these enormous birds evolved.
蛋壳还告诉我们，这些巨型鸟类是如何进化的。
It was known elephant birds were ratites-an ancient group of mostly big, flightless birds, including emus and cassowaries from Australia, ostriches from Africa, rheas from South America and others.
众所周知，象鸟属于平胸类鸟群，一种古老的无飞行能力的大型鸟，这类鸟包括澳大利亚的鸸鹋、鹤鸵，非洲的鸵鸟，南美的美洲鸵等。
So basically all those big flightless birds.
它们基本上是那些不会飞的大型鸟。
But they're actually most closely related to the kiwi bird, which is chicken size. So that's kind of surprising.
但它们实际上与几维鸟最接近，但几维鸟和鸡一样大。这有点令人惊讶。
And for a long time, scientists had a simple explanation for how these birds landed all over the world.
很长一段时间以来，科学家们对这些鸟类如何登陆世界各地有一个简单的解释。
Because they are mostly flightless and big, it was thought that there was a flightless common ancestor that was on the supercontinent called Gondwana.
因为这些鸟大多不会飞，体型又大，所以，人们认为它们在冈瓦纳超级大陆上存在一个不会飞的共同祖先。
And as Gondwana broke up, some populations were trapped on those different continents, and then, over time, they continued to diverge from each other, becoming more different.
随着冈瓦纳大陆的分裂，一些鸟群被困在不同的大陆上。随着时间的推移，鸟群继续分化，变得越来越不同。
These different lineages-the ostriches, the rheas, the elephant birds-split roughly when Gondwana did. That was the idea.
这些不同的谱系——鸵鸟、美洲鸵、象鸟——在冈瓦纳大陆分裂时大致分开了。这是以前的观点。
But the DNA data fouled up this hypothesis.
但是DNA数据推翻了这个假设。
DNA evidence shows that many of the ratite lineages split well after Gondwana broke up.
DNA证据显示，许多平胸类鸟系在冈瓦纳大陆分裂后分化得很好。
So how did these big flightless birds land all over the world?
那么这些不会飞的大鸟是如何登陆世界各地的呢?
The common ancestor therefore must have been very small and flying to each of the continents independently.
因此，共同的祖先体型一定很小，而且独立地飞往了每个大陆。
The data suggest the ancestor of these ground-bound, mostly big birds was actually small and airborne.
这些数据表明，这些在地面上活动的大型鸟类的祖先体型较小，可以飞行。
The fact that they're mostly flightless and large seems to be sort of a coincidence.
事实上，它们大多不会飞，而且体型很大，这似乎是一种巧合。
It looks like flightlessness evolved among the ratites at least six times independently, which is very surprising.
看起来平胸类鸟群无法飞行是至少独立进化六次的结果，这是非常令人惊讶的。
Surprising because it means that each of these big flightless birds-the elephant bird group included-seemed to take its own winding path to flightlessness and bigness.
令人惊讶，因为这意味着每一种不会飞的大型鸟——包括象鸟在内——似乎都经历了变得不会飞、变得更大的曲折道路。
It's a reminder, Alicia says, that in evolutionary history, the simplest or most obvious explanation isn't always the right one.
艾丽西娅指出，这是一个提醒，在进化史上，最简单或最明显的解释并不总是正确的。
So, yeah, elephant birds help change the way we think about the evolution of all birds, really.
没错，象鸟帮助我们改变了对所有鸟类进化的看法。
Science, Quickly is produced by Jeff DelViscio, Tulika Bose and Kelso Harper. Our theme music was composed by Dominic Smith.
“科学快播”栏目由杰夫·德尔维西奥、图利卡·博斯与凯尔索·哈珀制作。本栏目主题音乐由多米尼克·史密斯制作。
Don't forget to subscribe to Science, Quickly wherever you get your podcasts. Head over to ScientificAmerican.com for in-depth science news.
无论你从哪里打开播客，不要忘记订阅“科学快播”。前往ScientificAmerican.com获取深度科学新闻。
For Science, Quickly-I'm Flora Lichtman.
感谢收听“科学快播”--我是弗洛拉·里奇曼。
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