恐龍化石有疑問 古生物學(xué)家思索羽毛進(jìn)化過程

Paleontologists Ponder Feather Evolution

摘要： A beautifully preserved fossil from southern Germany raises questions about how feathers evolved from dinosaurs to birds, two paleontologists argue in a study published Thursday.從體形龐大的恐龍到身材嬌小的鳥類，動物的羽毛是如何進(jìn)化的？在德國南部發(fā)現(xiàn)的一具保存完好的恐龍化石日前引起了古生物學(xué)家們對動物羽毛進(jìn)化過程的思考。

A beautifully preserved fossil from southern Germany raises questions about how feathers evolved from dinosaurs to birds, two paleontologists argue in a study published Thursday.

The 150 million-year-old fossil is a juvenile carnivorous dinosaur about 2 1/2 feet long that scientists named Juravenator, for the Jura mountains where it was found.

It would have looked similar in life to the fleet-footed predators that menaced a young girl on the beach during the opening scene of "The Lost World," the second Jurassic Park movie.

The fossil#39;s exceptionally well-preserved bone structure clearly puts it among feathered kin on the dinosaur family tree. Because all of its close relatives are feathered, paleontologists would expect Juravenator to follow suit.

But a small patch of skin on the creature#39;s tail shows no sign of feathers. And the skin also doesn#39;t have the follicles that are typical of feathered dinosaurs, said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County. He and Ursula B. Gohlich of the University of Munich describe the fossil in Thursday#39;s issue of the journal Nature.

"It has a typical scaly dinosaurian skin," Chiappe said.

The paleontologists believe Juravenator#39;s closest known relative may have been a fully feathered dinosaur from China, Sinosauropterix.

There are a number of possible explanations for Juravenator#39;s nakedness. Feathers could have been lost on the evolutionary line leading to Juravenator after arising in an ancestor to both it and its feathered relatives. Or feathers could have evolved more than once in dinosaurs, cropping up in sister species at different times and places. It is also possible that this particular fossil of Juravenator, which appears to be a juvenile, only grew feathers as an adult or lost its feathers for part of the year.

But there is another possibility as well, said Mark Norell, curator of paleontology at the American Museum of Natural History: It is entirely possible that Juravenator did have feathers, but they simply failed to fossilize.

"Feathers are really just difficult things to preserve," Norell said.

To support his hypothesis he pointed out that several fossils of the oldest known bird, archaeopteryx, lack feathers.

Whether or not the new specimen raises interesting questions about how feathers — and thus birds — evolved, most experts do not see it as a challenge to the widely accepted view that modern birds are descended from dinosaurs.

從體形龐大的恐龍到身材嬌小的鳥類，動物的羽毛是如何進(jìn)化的？在德國南部發(fā)現(xiàn)的一具保存完好的恐龍化石日前引起了古生物學(xué)家們對動物羽毛進(jìn)化過程的思考。 【您現(xiàn)在閱讀的文章來自“中國人才指南網(wǎng)”，請記住我們的永久域名：m.szmdbiao.com 】

古生物學(xué)家聚焦恐龍羽毛

據(jù)美聯(lián)社3月15日報道，這具有1.5億年歷史的化石是一只大約2.5英尺長的幼年食肉恐龍留下來的，因?yàn)榘l(fā)現(xiàn)化石的地點(diǎn)位于侏羅山，因此科學(xué)家們稱它為Juravenator。

這具化石保存有異常完好的骨骼結(jié)構(gòu)，因此可以將其明確地歸入到恐龍家族中長有羽毛的一類。由于它所有的近親都長著羽毛，所以考古學(xué)家認(rèn)為Juravenator也是如此。

但考古學(xué)家們發(fā)現(xiàn)，Juravenator尾部殘留的一小塊皮膚卻絲毫顯示不出它曾長有羽毛的跡象。美國洛杉磯縣自然歷史博物館恐龍研究院負(fù)責(zé)人劉易斯·齊亞比說，這塊皮膚上也沒有長羽毛的恐龍所擁有的典型的羽囊。齊亞比說，“這是典型的有鱗恐龍的皮膚”。齊亞比和德國慕尼黑大學(xué)的研究人員厄休拉·高立克在周四（3月16日）出版的《自然》雜志上闡述了他們的上述觀點(diǎn)。

這些古生物學(xué)家們相信，已知的與Juravenator關(guān)系最為緊密的親屬可能要數(shù)中國的一種全身長有羽毛的恐龍——中華龍鳥。

恐龍為何無羽的多種可能

對于Juravenator為何沒有羽毛，可能的解釋有很多。其中之一認(rèn)為，在通向Juravenator的進(jìn)化道路上，羽毛可能消失了。或者，羽毛在恐龍身上不是首次進(jìn)化，這種進(jìn)化突然發(fā)生在不同時間和地點(diǎn)的相似種類的恐龍身上。還可能因?yàn)�，這是Juravenator幼年時期的化石，而它只有在成年后才會長出羽毛。

美國自然歷史博物館的古生物學(xué)家馬克·諾萊爾還提出了另外一種說法，即完全有可能Juravenator的確長有羽毛，但是這些羽毛卻沒能形成化石。諾萊爾說：“羽毛確實(shí)是很難保存下來的東西�！睘榱俗C明這種觀點(diǎn)，他指出，已知的最早的鳥類——始祖鳥的一些化石也沒有羽毛。

報道說，無論這個新發(fā)現(xiàn)的化石是否引起人們，對羽毛及鳥類進(jìn)化過程的新質(zhì)疑，但大多專家認(rèn)為，它不會對人們已普遍接受的現(xiàn)代鳥類是由恐龍進(jìn)化而來的這個觀點(diǎn)構(gòu)成挑戰(zhàn)。

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