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。

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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。