南美洲发现迄今最古老的啮齿动物化石
文章来源:未知 文章作者:enread 发布时间:2011-10-13 02:00 字体: [ ]  进入论坛
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In a literal walk through time along the Ucayali River near Contamana, Peru, a team of researchers found rodent1(啮齿动物) fossils at least 41 million years old -- by far the oldest on the South American continent. The remains2 -- teeth -- showed these mouse- and rat-size animals are most closely related to African rodents3, confirming the hypothesis that early rodents of South America had origins in Africa, said Darin Croft, an anatomy4(解剖学) professor at the Case Western Reserve University School of Medicine and member of the research team.

This discovery supports the contention5 that rodents landed in the north and spread south. The rodents are from the suborder Caviomorpha, the group that includes living rodents such as guinea pigs, chinchillas, and New World porcupines6. The oldest fossils from this group are only about 32 million years old in central Chile and about 30 million years old in Patagonia, Argentina,. Taken all together, the pattern contradicts the theory of a northward7 expansion deduced from the fossil record 20 years ago.

The findings, which describe three new species, are published online in Proceedings8 of the Royal Society B.

"This really pushes back the date of the first South American rodents," said Croft, a paleontologist(古生物学者) who specializes in mammalian evolution.

Pierre-Olivier Antoine, a professor of paleontology in the Institute of Evolutionary9 Sciences at Montpellier University in southern France, asked Croft to join the team of scientists from France, Germany, Peru and Panama. Members first flew into the region in 2008, after reading Harvard Geology Professor Bernhard Kummel's 1948 description of the area.

Kummel mentions fossils along the Ucayali, a major tributary10(属国,支流) of the Amazon, but the team found no evidence that anyone had investigated them.

During three trips from 2008 to 2010, Antoine's group found the fossils in a portion of the riverbank exposed when the water level is low.

The geology along the river showed that layers of rock, including the fossil layer, had been pushed up in a rainbow-shaped fold, called an anticline. The layers that had once been above or below the fossils turned from horizontal to nearly vertical11. Instead of digging down to the past, the scientists walked downstream from the fossil layer to go back in time, upstream to go forward in time.

Ash found among silt12 particles 47 meters forward in time was dated at 41 million years ago using argon-argon radioactive dating, providing the minimum age of the fossils.

The date is supported by genetic13 studies of living African and South American rodents that show the animals are of common origin and estimate the animals arrived in South America during the Mid-Eocene Climatic Optimum, or about 40 million years ago.

At that time, other scientists estimate, an African rodent on a raft of vegetation could have reached Northeast Brazil in one to two weeks.

The characteristics of the teeth found reinforce the connection between the continents: the morphologies(形态学) are closest to those of African rodents.

The dental features indicate the rodents probably ate soft seeds and plant parts as many small rodents do today.

Pollen14 extracted from the fossilized mud that contained the teeth suggests these rodents lived in a rain forest, much like the rain forest there today.



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1 rodent DsNyh     
n.啮齿动物;adj.啮齿目的
参考例句:
  • When there is a full moon,this nocturnal rodent is careful to stay in its burrow.月圆之夜,这种夜间活动的啮齿类动物会小心地呆在地洞里不出来。
  • This small rodent can scoop out a long,narrow tunnel in a very short time.这种小啮齿动物能在很短的时间里挖出一条又长又窄的地道来。
2 remains 1kMzTy     
n.剩余物,残留物;遗体,遗迹
参考例句:
  • He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
  • The remains of the meal were fed to the dog.残羹剩饭喂狗了。
3 rodents 1ff5f0f12f2930e77fb620b1471a2124     
n.啮齿目动物( rodent的名词复数 )
参考例句:
  • Rodents carry diseases and are generally regarded as pests. 啮齿目动物传播疾病,常被当作害虫对待。 来自《简明英汉词典》
  • Some wild rodents in Africa also harbor the virus. 在非洲,有些野生啮齿动物也是储毒者。 来自辞典例句
4 anatomy Cwgzh     
n.解剖学,解剖;功能,结构,组织
参考例句:
  • He found out a great deal about the anatomy of animals.在动物解剖学方面,他有过许多发现。
  • The hurricane's anatomy was powerful and complex.对飓风的剖析是一项庞大而复杂的工作。
5 contention oZ5yd     
n.争论,争辩,论战;论点,主张
参考例句:
  • The pay increase is the key point of contention. 加薪是争论的焦点。
  • The real bone of contention,as you know,is money.你知道,争论的真正焦点是钱的问题。
6 porcupines 863c07e5a89089680762a3ad5a732827     
n.豪猪,箭猪( porcupine的名词复数 )
参考例句:
  • Porcupines use their spines to protect themselves. 豪猪用身上的刺毛来自卫。
  • The59 victims so far include an elephant, dromedaries, monkeys and porcupines. 目前为止,死亡的动物包括大象、峰骆驼、子以及豪猪。 来自互联网
7 northward YHexe     
adv.向北;n.北方的地区
参考例句:
  • He pointed his boat northward.他将船驶向北方。
  • I would have a chance to head northward quickly.我就很快有机会去北方了。
8 proceedings Wk2zvX     
n.进程,过程,议程;诉讼(程序);公报
参考例句:
  • He was released on bail pending committal proceedings. 他交保获释正在候审。
  • to initiate legal proceedings against sb 对某人提起诉讼
9 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
10 tributary lJ1zW     
n.支流;纳贡国;adj.附庸的;辅助的;支流的
参考例句:
  • There was a tributary road near the end of the village.村的尽头有条岔道。
  • As the largest tributary of Jinsha river,Yalong river is abundant in hydropower resources.雅砻江是金沙江的最大支流,水力资源十分丰富。
11 vertical ZiywU     
adj.垂直的,顶点的,纵向的;n.垂直物,垂直的位置
参考例句:
  • The northern side of the mountain is almost vertical.这座山的北坡几乎是垂直的。
  • Vertical air motions are not measured by this system.垂直气流的运动不用这种系统来测量。
12 silt tEHyA     
n.淤泥,淤沙,粉砂层,泥沙层;vt.使淤塞;vi.被淤塞
参考例句:
  • The lake was almost solid with silt and vegetation.湖里几乎快被淤泥和植物填满了。
  • During the annual floods the river deposits its silt on the fields.每年河水泛滥时都会在田野上沉积一层淤泥。
13 genetic PgIxp     
adj.遗传的,遗传学的
参考例句:
  • It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
  • Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。
14 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。
TAG标签: species American rodent
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