短吻鳄与鸟类有着相同的肺结构与祖先
文章来源:未知 文章作者:meng 发布时间:2010-01-18 00:26 字体: [ ]  进入论坛
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Alligators2 and birds share a breathing mechanism3 which may have helped their ancestors dominate Earth more than 200 million years ago, scientists say.

科学家称,短吻鳄与鸟类有着相同的呼吸机制,这可能有助于它们的祖先在2亿年前统治地球。

How do alligators breathe?
How do alligators breathe?

Research published in the journal Science found that like birds, in alligators短吻鳄 air flows in one direction.

Birds' lung structure allows them to breathe when flying in low oxygen, or hypoxic低氧的, conditions.

This breathing may have helped a common ancestor of birds and alligators thrive繁荣,兴旺 in the hypoxic period of the Triassic三叠纪的.

Mammals 'hiding'

"It might explain a mystery that has been around for quite some time", Dr Colleen Farmer from the University of Utah told BBC News.

The mystery in question is why the archosaurs祖龙,古蜥 came to dominate Earth after the planet's worst mass extinction4 251 million years ago.

Archosaurs evolved into two different branches which developed into crocodilians鳄目动物, dinosaurs5, flying pterosaurs飞龙目 and eventually birds.

Synapsids, which evolved to include mammals, had been dominant6 in the Permian period before the mass extinction.

Some survived but were toppled倾覆,推翻 from their perch栖息,栖木 by the archosaurs.

Any mammal-like synapsid合弓纲 survivors8 "were teeny极小的,微小的 liittle things hiding in cracks" said Dr Farmer. "I think it's because they couldn't compete.

"It wasn't until the die-off of the large dinosaurs 65 million years ago that mammals made a comeback and started occupying body sizes larger than an opossum负鼠."

To demonstrate alligator1 lung mechanisms9, the scientists measured airflow in anesthetised animals局部麻醉动物, showing it flows in one direction rather than in and out of chambers10.

They also pumped water containing tiny fluorescent荧光的 beads12玻璃粉 into the lungs of dead alligators to observe the flow.

Puzzle solved

The researchers believe the similarity in lung structure may explain why some animals were better able to adapt after the extinction, when oxygen levels dropped.

"We know that birds are really good at breathing in hypoxic conditions. They can fly at altitudes高度 that would kill a mammal," said Dr Farmer.

"Many archosaurs, such as pterosaurs, apparently13 were capable of sustaining vigorous exercise. Lung design may have played a key role in this capacity.

"That's been a puzzle, why do birds have these very different lungs? But now we can date it back to the common ancestor of birds and crocodilians.

"It implies that all dinosaurs, herbivores食草动物 like Triceratops and carnivores食肉动物 like Tyrannosaurus, had bird-like lungs," Dr Farmer added.



点击收听单词发音收听单词发音  

1 alligator XVgza     
n.短吻鳄(一种鳄鱼)
参考例句:
  • 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 )
参考例句:
  • 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 mechanism zCWxr     
n.机械装置;机构,结构
参考例句:
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
4 extinction sPwzP     
n.熄灭,消亡,消灭,灭绝,绝种
参考例句:
  • 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 dinosaurs 87f9c39b9e3f358174d58a584c2727b4     
n.恐龙( dinosaur的名词复数 );守旧落伍的人,过时落后的东西
参考例句:
  • 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》
6 dominant usAxG     
adj.支配的,统治的;占优势的;显性的;n.主因,要素,主要的人(或物);显性基因
参考例句:
  • 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 perch 5u1yp     
n.栖木,高位,杆;v.栖息,就位,位于
参考例句:
  • The bird took its perch.鸟停歇在栖木上。
  • Little birds perch themselves on the branches.小鸟儿栖歇在树枝上。
8 survivors 02ddbdca4c6dba0b46d9d823ed2b4b62     
幸存者,残存者,生还者( survivor的名词复数 )
参考例句:
  • The survivors were adrift in a lifeboat for six days. 幸存者在救生艇上漂流了六天。
  • survivors clinging to a raft 紧紧抓住救生筏的幸存者
9 mechanisms d0db71d70348ef1c49f05f59097917b8     
n.机械( mechanism的名词复数 );机械装置;[生物学] 机制;机械作用
参考例句:
  • The research will provide direct insight into molecular mechanisms. 这项研究将使人能够直接地了解分子的机理。 来自《简明英汉词典》
  • He explained how the two mechanisms worked. 他解释这两台机械装置是如何工作的。 来自《简明英汉词典》
10 chambers c053984cd45eab1984d2c4776373c4fe     
n.房间( chamber的名词复数 );(议会的)议院;卧室;会议厅
参考例句:
  • The body will be removed into one of the cold storage chambers. 尸体将被移到一个冷冻间里。 来自《简明英汉词典》
  • Mr Chambers's readable book concentrates on the middle passage: the time Ransome spent in Russia. Chambers先生的这本值得一看的书重点在中间:Ransome在俄国的那几年。 来自互联网
11 fluorescent Zz2y3     
adj.荧光的,发出荧光的
参考例句:
  • They observed the deflections of the particles by allowing them to fall on a fluorescent screen.他们让粒子落在荧光屏上以观察他们的偏移。
  • This fluorescent lighting certainly gives the food a peculiar color.这萤光灯当然增添了食物特别的色彩。
12 beads 894701f6859a9d5c3c045fd6f355dbf5     
n.(空心)小珠子( bead的名词复数 );水珠;珠子项链
参考例句:
  • a necklace of wooden beads 一条木珠项链
  • Beads of perspiration stood out on his forehead. 他的前额上挂着汗珠。
13 apparently tMmyQ     
adv.显然地;表面上,似乎
参考例句:
  • 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。
TAG标签: birds alligators ancestors
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