文章来源:未知 文章作者:meng 发布时间:2010-01-15 00:46 字体: [ ]  进入论坛

University of Utah scientists discovered that air flows in one direction as it loops through依次通过 the lungs of alligators2短吻鳄鱼, just as it does in birds. The study suggests this breathing method may have helped the dinosaurs3' ancestors dominate Earth after the planet's worst mass extinction4 251 million years ago. Before and until about 20 million years after the extinction – called "the Great Dying" or the Permian二叠纪的-Triassic三叠纪的 extinction – mammal-like reptiles爬行类 known as synapsids were the largest land animals on Earth.

The extinction killed 70 percent of land life and 96 percent of sea life. As the planet recovered during the next 20 million years, archosaurs祖龙,古蜥 (Greek for "ruling lizards") became Earth's dominant6 land animals. They evolved into two major branches on the tree of life: crocodilians鳄目动物, or ancestors of crocodiles and alligators, and a branch that produced flying pterosaurs飞龙目,翼龙目, dinosaurs and eventually birds, which technically7 are archosaurs.

By demonstrating one-way or "unidirectional" airflow within the lungs of alligators, the new study – published in the Friday, Jan. 15 issue of the journal Science – means that such a breathing pattern likely evolved before 246 million years ago, when crocodilians split from the branch of the archosaur family tree that led to pterosaurs, dinosaurs and birds.

That, in turn, means one-way airflow evolved in archosaurs earlier than once thought, and may explain why those animals came to dominance in the Early Triassic Period, after the extinction and when the recovering ecosystem8 was warm and dry, with oxygen levels perhaps as low as 12 percent of the air compared with 21 percent today.

"The real importance of this air-flow discovery in gators佛州大鳄 is it may explain the turnover9 in fauna10动物群,动物区系 between the Permian and the Triassic, with the synapsids losing their dominance and being supplanted11 by these archosaurs," says C.G. Farmer, the study's principal author and an assistant professor of biology at the University of Utah. "That's the major reason this is important scientifically."

Even with much less oxygen in the atmosphere, "many archosaurs, such as pterosaurs, apparently12 were capable of sustaining vigorous有力的,精力充沛的 exercise," she adds. "Lung design may have played a key role in this capacity because the lung is the first step in the cascade喷流,层叠 of oxygen from the atmosphere to the animal's tissues, where it is used to burn fuel for energy."

Farmer emphasized the discovery does not explain why dinosaurs, which first arose roughly 230 million years ago, eventually outcompeted other archosaurs.

Farmer conducted the study – funded by the National Science Foundation – with Kent Sanders, an associate professor of radiology放射学 at the University of Utah School of Medicine. They performed CT scans of a 4-foot-long, 24-pound alligator1.


1 alligator XVgza     
  • She wandered off to play with her toy alligator.她开始玩鳄鱼玩具。
  • Alligator skin is five times more costlier than leather.鳄鱼皮比通常的皮革要贵5倍。
2 alligators 0e8c11e4696c96583339d73b3f2d8a10     
n.短吻鳄( alligator的名词复数 )
  • Two alligators rest their snouts on the water's surface. 两只鳄鱼的大嘴栖息在水面上。 来自辞典例句
  • In the movement of logs by water the lumber industry was greatly helped by alligators. 木材工业过去在水上运输木料时所十分倚重的就是鳄鱼。 来自辞典例句
3 dinosaurs 87f9c39b9e3f358174d58a584c2727b4     
n.恐龙( dinosaur的名词复数 );守旧落伍的人,过时落后的东西
  • The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
  • Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》
4 extinction sPwzP     
  • The plant is now in danger of extinction.这种植物现在有绝种的危险。
  • The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。
5 reptiles 45053265723f59bd84cf4af2b15def8e     
n.爬行动物,爬虫( reptile的名词复数 )
  • Snakes and crocodiles are both reptiles. 蛇和鳄鱼都是爬行动物。 来自《简明英汉词典》
  • Birds, reptiles and insects come from eggs. 鸟类、爬虫及昆虫是卵生的。 来自《现代汉英综合大词典》
6 dominant usAxG     
  • The British were formerly dominant in India.英国人从前统治印度。
  • She was a dominant figure in the French film industry.她在法国电影界是个举足轻重的人物。
7 technically wqYwV     
  • Technically it is the most advanced equipment ever.从技术上说,这是最先进的设备。
  • The tomato is technically a fruit,although it is eaten as a vegetable.严格地说,西红柿是一种水果,尽管它是当作蔬菜吃的。
8 ecosystem Wq4xz     
  • This destroyed the ecosystem of the island.这样破坏了岛上的生态系统。
  • We all have an interest in maintaining the integrity of the ecosystem.维持生态系统的完整是我们共同的利益。
9 turnover nfkzmg     
  • The store greatly reduced the prices to make a quick turnover.这家商店实行大减价以迅速周转资金。
  • Our turnover actually increased last year.去年我们的营业额竟然增加了。
10 fauna 9kExx     
  • This National Park is an area with unique fauna and flora.该国家公园区域内具有独特的动物种群和植物种群。
  • Fauna is a biological notion means all the animal life in a particular region or period. 动物群是一个生物学的概念,指的是一个特定时期或者地区的所有动物。
11 supplanted 1f49b5af2ffca79ca495527c840dffca     
把…排挤掉,取代( supplant的过去式和过去分词 )
  • In most offices, the typewriter has now been supplanted by the computer. 当今许多办公室里,打字机已被电脑取代。
  • The prime minister was supplanted by his rival. 首相被他的政敌赶下台了。
12 apparently tMmyQ     
  • An apparently blind alley leads suddenly into an open space.山穷水尽,豁然开朗。
  • He was apparently much surprised at the news.他对那个消息显然感到十分惊异。
13 cascade Erazm     
  • She watched the magnificent waterfall cascade down the mountainside.她看着壮观的瀑布从山坡上倾泻而下。
  • Her hair fell over her shoulders in a cascade of curls.她的卷发像瀑布一样垂在肩上。
TAG标签: air birds gators