恐龙如何飞上天空 / 四六文摘

Scientists have long known that many early dinosaurs, the ancestors of today’s birds, were covered in feathers, likely for warmth and to attract mates.

科学家们早就知道，许多早期恐龙，即今天鸟类的祖先，它们身上覆盖着羽毛，可能是为了保暖和吸引配偶。

But no one knows exactly when—and how—these feathered dinos took flight.

但是没有人确切知道这些长着羽毛的恐龙是何时以及如何飞行的。

Now, molecular evidence from feathered dinosaur fossils reveals how the key proteins that make up feathers became lighter and more flexible over time, as flightless dinosaurs evolved into flying ones—and later, birds.

现在，来自有羽毛恐龙化石的分子证据揭示了随着时间的推移，组成羽毛的关键蛋白质是如何变得更轻、更灵活的，随之不会飞的恐龙进化成了会飞的恐龙——后来进化成了鸟类。

All modern land animals with backbones have keratins, proteins that make up everything from fingernails and beaks, to scales and feathers.

所有有脊椎的现代陆地动物都有角蛋白，这种蛋白质构成了从指甲、喙到鳞片和羽毛的所有东西。

In humans and other mammals, α-keratins form the 10 nanometerwide filaments that make up hair, skin, and nails.

在人类和其他哺乳动物,α-角蛋白形成10纳米直径的细丝，然后组成的头发,皮肤和指甲。

In crocodiles, turtles, lizards, and birds, β-keratins form the even narrower, more rigid filaments that build claws, beaks, and feathers.

在鳄鱼、乌龟、蜥蜴、鸟类,β-角蛋白甚至会形成更窄,更严格的细丝构建爪子,喙和羽毛。

Using the whole genomes of dozens of living birds, crocodiles, turtles, and other reptiles, scientists have built over the past decade a family tree of these animals based on how their β-keratins changed over time.

利用现存的鸟类,鳄鱼,海龟,和其他爬行动物的整个基因组，基于他们的这些动物β-角蛋白随着时间的推移进行的改变，科学家们建立了在过去的十年里一个家族树。

Among the revelations: Modern birds have lost most of their α-keratins, but β-keratins in their feathers have become more flexible, thanks to a missing swath of glycine and tyrosine amino acids that make claws and beaks rigid.

他们发现:现代鸟类失去了大部分α-角蛋白,但在他们的羽毛中的β-角蛋白变得更加灵活,这是由于缺失的甘氨酸和酪氨酸的氨基酸列使得爪子和喙具有了刚性。

This suggests that the transition to flight required both changes to take place.

这表明，向飞行的过渡需要进行这两种改变。

Now, researchers have shown this directly by analyzing the α- and β-keratins in a handful of exceptionally preserved fossils from China and Mongolia.

如今，研究人员们通过分析少数保存完好的来自中国和蒙古的化石中的α- and β-角蛋白直接显示了这一点。

The researchers, led by paleontologists Pan Yanhong of the Chinese Academy of Sciences in Beijing and Mary Schweitzer of North Carolina State University in Raleigh, designed separate antibodies to bind to identifying segments of various α- and β-keratin proteins preserved in the fossilized feathers of five species that lived between 160 million and 75 million years ago.

研究人员由北京的中科院的古生物学家潘艳红和位于罗利市的北卡罗莱纳州立大学的玛丽.史威泽教授带领,他们设计出了单独的抗体用来结合并识别出不同的α-和β-角蛋白片段，这些片段保存在距今1.6亿至7500万年的五种生物的羽毛化石中。

The antibodies were labeled with fluorescent tags that light up whenever they bind to their targets.

这些抗体被贴上荧光标记，每当它们与目标结合时，荧光标记就会亮起来。

The feathers of Anchiornis, a crow-size feathered dinosaur that lived 160 million years ago, lit up to reveal the flexible truncated β-keratin found in modern birds, the researchers report today in Proceedings of the National Academy of Sciences.

近鸟龙的羽毛,其荧光的点亮揭示了灵活截断的β-角蛋白的存在，这是一种奇特长有羽毛的恐龙生活在1.6亿年前，研究人员今天在美国国家科学院院刊》上发表了报告。

But the dinosaurs—which predate the first recognized bird, Archaeopteryx, by 10 million years—had even more α-keratins, which are largely absent from bird feathers today.

而这种恐龙，它会猎食之前公认的最早的始祖鸟，生活在大约在一千万年前，它的α角蛋白还更多，这种蛋白在如今的鸟类羽毛中是大量缺失的。

Given that, plus structural differences revealed by electron microscopy analysis, it’s likely that Anchiornis feathers weren’t suitable for flight, Schweitzer says, but represent an intermediate stage in the evolution toward flight feathers.

史威泽说，考虑到这一点，再加上电子显微镜分析显示的结构差异，近鸟龙的羽毛可能不适合飞行，但它代表了向飞行羽毛进化的中间阶段。

Fossilized feathers from a 130 million-year-old small flightless dinosaur called Shuvuuia (which is not an ancestor to today’s birds) reveal that, like modern birds, it lacked α-keratins.

而从一种一亿三千万年前的小羽毛不会飞的叫做叫Shuvuuia的恐龙化石中显示(它不是今天鸟类的祖先),与现代鸟类一样,它缺乏α-角蛋白。

But unlike Anchiornis, its feathers were still made up of the larger, more rigid β-keratins.

但与近鸟龙不同,它的羽毛仍由更大的,更多的刚性β-角蛋白组成。

“We’re beginning to uncover the mosaic pattern of feather evolution,” Schweitzer says, which suggests the transition of feathers to flight required both the mutations that eliminated most α-keratins and the truncated flexible β-keratins.

“我们开始发现了羽毛进化的某些秘密了,“史威泽说,这表明羽毛向飞行过渡所需的突变,在于消除大多数α-角蛋白和β-角蛋白片段变得灵活。

“This type of work is every evolutionary biologist’s dream,” says Matthew Greenwold, an evolutionary biologist at the University of South Carolina in Columbia, who helped build the earlier β-keratin family tree.

”这种类型的工作是每一个进化生物学家的梦想,”马修.格林沃德说，他是位于哥伦比亚市的南卡罗莱纳大学的进化生物学家,早些时候曾帮助建立β-keratin家谱。

Taken together with modern genetic evidence, the new finding suggests that during the transition to flight, the β-keratin gene was duplicated many times in the genomes of some dinosaurs.

结合现代遗传学证据,新的发现表明,过渡到飞行期间,β-角蛋白基因在恐龙的基因组重复了很多次。

As the animals evolved, some of the extra copies then mutated into the truncated form that made flight possible.

随着动物的进化，一些多余的拷贝突变成截短的形式，从而使飞行成为可能。

That not only allowed feathered dinosaurs such as Archaeopteryxto cruise the skies around 150 million years ago, but it also gave rise to all the crows, finches, starlings, and eagles we have with us today.

这不仅让始祖鸟等有羽毛的恐龙在大约1.5亿年前飞上了天空，而且还造就了我们今天所拥有的乌鸦、雀鸟、椋鸟和老鹰。