恐龙死亡导致鱼类增多

Dinosaur¹ Death Leads to Rise of Fish 恐龙死亡导致鱼类增多

Tens of millions of years ago, an asteroid² hit what is now the Yucatan Peninsula of Mexico. The event led to a global mass extinction³ that has been linked to the end of the dinosaurs⁴. New research shows what that great disaster led to: a modern age of fish.

Sixty-six million years ago, the ocean was a different place. Sharks and octopus-like creatures were powerful. But, scientist Elizabeth Sibert says there were other important species as well.

"There were also many marine⁵ reptiles⁶ that were swimming around. And of course there were fish. Absolutely there were ray-finned fish around. It's just that they weren't very dominant⁷."

Ms. Sibert is a graduate student at the University of California, San Diego. She and her professor compared micro-fossil fish teeth and shark scales in sediment⁸ that dated before and after the mass death.

"Basically the deeper down you get, the older you get.  So we looked at sediments⁹ from 75 million years ago to about 45 million years ago, looking every 200,000 years in some cases, looking at every 10,000 years in other cases."

Fossil evidence showed that the ratio of fish to shark changed sharply after the asteroid hit. Elizabeth Sibert explains.

"We see that instead of having about equal number of shark fossils and fish fossils, we see that the fish fossils more than double and that trend continues while the shark fossils stay approximately the same."

The study suggests that the mass extinction killed many animals at both the top and bottom of the ocean food chain. This permitted animals in the middle of the chain to increase their numbers. Those animals are the ray-finned fish that represent nearly all fish species today.

"And they radiated into all these newly vacated spots, and possibly some new things that wouldn't have existed at all if the extinction hadn't happened."

Elizabeth Sibert says her next step is to go back to the micro-fossil record. She will try to learn from it how the fish dealt with other stresses in the ocean, like global warming.   

Words in This Story

extinction – n. the state or situation that results when something (such as a plant or animal species) has died out completely

sediment – n. tiny pieces of rock and other material that settle at the bottom of the ocean

ratio – n. the relationship that exists between the size, number, or amount of two things and that is often represented by two numbers

food chain – n. a series of living things in which each one uses the next lower member of the series as a source of food

vacate --– v. to leave empty or open

1 dinosaur   

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 asteroid   

n.小行星；海盘车(动物)

参考例句：

• Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
• It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。

3 extinction   

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 dinosaurs   

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》

5 marine   

adj.海的；海生的；航海的；海事的；n.水兵

参考例句：

• Marine creatures are those which live in the sea. 海洋生物是生存在海里的生物。
• When the war broke out,he volunteered for the Marine Corps.战争爆发时，他自愿参加了海军陆战队。

6 reptiles   

n.爬行动物，爬虫( reptile的名词复数 )

参考例句：

• 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》

7 dominant   

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。

8 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

9 sediments   

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。