科学家发现恐龙大灭绝前最年幼的化石
文章来源:未知 文章作者:enread 发布时间:2011-07-13 02:13 字体: [ ]  进入论坛
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A team of scientists has discovered the youngest dinosaur1 preserved in the fossil record before the catastrophic meteor(流星) impact 65 million years ago. The finding indicates that dinosaurs2 did not go extinct prior to the impact and provides further evidence as to whether the impact was in fact the cause of their extinction3. Researchers from Yale University discovered the fossilized horn of a ceratopsian(角龙) – likely a Triceratops, which are common to the area – in the Hell Creek4 formation in Montana last year. They found the fossil buried just five inches below the K-T boundary, the geological layer that marks the transition from the Cretaceous period to the Tertiary period at the time of the mass extinction that took place 65 million years ago.

Since the impact hypothesis for the demise5 of the dinosaurs was first proposed more than 30 years ago, many scientists have come to believe the meteor caused the mass extinction and wiped out the dinosaurs, but a sticking point has been an apparent lack of fossils buried within the 10 feet of rock below the K-T boundary. The seeming anomaly(异常,不规则) has come to be known as the "three-meter gap." Until now, this gap has caused some paleontologists(古生物学者) to question whether the non-avian dinosaurs of the era – which included Tyrannosaurus rex, Triceratops, Torosaurus and the duckbilled dinosaurs – gradually went extinct sometime before the meteor struck. (Avian dinosaurs survived the impact, and eventually gave rise to modern-day birds.)

"This discovery suggests the three-meter gap doesn't exist," said Yale graduate student Tyler Lyson, director of the Marmarth Research Foundation and lead author of the study, published online July 12 in the journal Biology Letters. "The fact that this specimen6 was so close to the boundary indicates that at least some dinosaurs were doing fine right up until the impact."

While the team can't determine the exact age of the dinosaur, Lyson said it likely lived tens of thousands to just a few thousand years before the impact. "This discovery provides some evidence that dinosaurs didn't slowly die out before the meteor struck," he said.

Eric Sargis, curator of vertebrate paleontology at the Yale Peabody Museum of Natural History, and graduate student Stephen Chester discovered the ceratopsian last year while searching for fossilized mammals that evolved after the meteor impact. At first, Lyson said, the team thought it was buried within about three feet of the K-T boundary, but were surprised to learn just how close to the boundary – and hence, how close in time to the impact – it was. They sent soil samples to a laboratory to determine the exact location of the boundary, which is marked by the relative abundance of certain types of fossilized pollen7 and other geological indicators8 but is difficult to determine visually while in the field.

Because the dinosaur was buried in a mudstone floodplain(泛滥平原) , the team knew it hadn't been re-deposited from older sediments9, which can sometimes happen when fossils are found in riverbeds that may have eroded10 and re-distributed material over time.

The team is now examining other fossil specimens11 that appear to be buried close to the K-T boundary and expect to find more, Lyson said. He suspects that other fossils discovered in the past may have been closer to the boundary than originally thought and that the so-called three-meter gap never existed.

"We should be able to verify that using the more sophisticated soil analysis technique rather than estimating the boundary's location based solely12 on a visual examination of the rock formations while in the field, which is what has typically been done in the past," Lyson said.



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1 dinosaur xuSxp     
n.恐龙
参考例句:
  • Are you trying to tell me that David was attacked by a dinosaur?你是想要告诉我大卫被一支恐龙所攻击?
  • He stared at the faithful miniature of the dinosaur.他凝视著精确的恐龙缩小模型。
2 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》
3 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。
4 creek 3orzL     
n.小溪,小河,小湾
参考例句:
  • He sprang through the creek.他跳过小河。
  • People sunbathe in the nude on the rocks above the creek.人们在露出小溪的岩石上裸体晒日光浴。
5 demise Cmazg     
n.死亡;v.让渡,遗赠,转让
参考例句:
  • He praised the union's aims but predicted its early demise.他赞扬协会的目标,但预期这一协会很快会消亡。
  • The war brought about the industry's sudden demise.战争道致这个行业就这么突然垮了。
6 specimen Xvtwm     
n.样本,标本
参考例句:
  • You'll need tweezers to hold up the specimen.你要用镊子来夹这标本。
  • This specimen is richly variegated in colour.这件标本上有很多颜色。
7 pollen h1Uzz     
n.[植]花粉
参考例句:
  • Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。
  • He developed an allergy to pollen.他对花粉过敏。
8 indicators f46872fc1b5f08e9d32bd107be1df829     
(仪器上显示温度、压力、耗油量等的)指针( indicator的名词复数 ); 指示物; (车辆上的)转弯指示灯; 指示信号
参考例句:
  • The economic indicators are better than expected. 经济指标比预期的好。
  • It is still difficult to develop indicators for many concepts used in social science. 为社会科学领域的许多概念确立一个指标仍然很难。
9 sediments 8b3acb612b624abdf2c2881bc6928565     
沉淀物( sediment的名词复数 ); 沉积物
参考例句:
  • When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后,体积的70-80%是水。
  • Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。
10 eroded f1d64e7cb6e68a5e1444e173c24e672e     
adj. 被侵蚀的,有蚀痕的 动词erode的过去式和过去分词形式
参考例句:
  • The cliff face has been steadily eroded by the sea. 峭壁表面逐渐被海水侵蚀。
  • The stream eroded a channel in the solid rock. 小溪在硬石中侵蚀成一条水道。
11 specimens 91fc365099a256001af897127174fcce     
n.样品( specimen的名词复数 );范例;(化验的)抽样;某种类型的人
参考例句:
  • Astronauts have brought back specimens of rock from the moon. 宇航员从月球带回了岩石标本。
  • The traveler brought back some specimens of the rocks from the mountains. 那位旅行者从山上带回了一些岩石标本。 来自《简明英汉词典》
12 solely FwGwe     
adv.仅仅,唯一地
参考例句:
  • Success should not be measured solely by educational achievement.成功与否不应只用学业成绩来衡量。
  • The town depends almost solely on the tourist trade.这座城市几乎完全靠旅游业维持。
TAG标签: dinosaur fossil extinction
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