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该题平均耗时:3m54s,平均正确率:75.2% 添加做题笔记

Two opposing scenarios, the “arboreal” hypothesis and the “cursorial” hypothesis, have traditionally been put forward concerning the origins of bird flight. The “arboreal” hypothesis holds that bird ancestors began to fly by climbing trees and gliding down from branches with the help of incipient feathers: the height of trees provides a good starting place for launching flight, especially through gliding. As feathers became larger over time, flapping flight evolved and birds finally became fully air-borne. This hypothesis makes intuitive sense, but certain aspects are troubling. Archaeopteryx (the earliest known bird) and its maniraptoran dinosaur cousins have no obviously arboreal adaptations, such as feet fully adapted for perching. Perhaps some of them could climb trees, but no convincing analysis has demonstrated how Archaeopteryx would have both climbed and flown with its forelimbs, and there were no plants taller than a few meters in the environments where Archaeopteryx fossils have been found. Even if the animals could climb trees, this ability is not synonymous with gliding ability. (Many small animals, and even some goats and kangaroos, are capable of climbing trees but are not gliders.) Besides, Archaeopteryx shows no obvious features of gliders, such as a broad membrane connecting forelimbs and hind limbs.

The “cursorial”(running) hypothesis holds that small dinosaurs ran along the ground and stretched out their arms for balance as they leaped into the air after insect prey or, perhaps, to avoid predators. Even rudimentary feathers on forelimbs could have expanded the arm’s surface area to enhance lift slightly. Larger feathers could have increased lift incrementally, until sustained flight was gradually achieved. Of course, a leap into the air does not provide the acceleration produced by dropping out of a tree; an animal would have to run quite fast to take off. Still, some small terrestrial animals can achieve high speeds. The cursorial hypothesis is strengthened by the fact that the immediate theropod dinosaur ancestors of birds were terrestrial, and they had the traits needed for high lift off speeds: they were small, agile, lightly built, long-legged, and good runners. And because they were bipedal, their arms were free to evolve flapping flight, which cannot be said for other reptiles of their time.

The passage suggests which of the following regarding the climbing ability of Archaeopteryx?


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  • 分析D选项
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  • 分析E选项
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暂无雷哥网文字解析
当前版本由 bella 更新于2015-11-24 10:19:51 感谢由 bella 对此题目的解答所做出的贡献。

a爬树的能力被初羽阻碍,不对

b没有比较两者之间谁会爬树

c说它有一种爬树的体征,原文说have no obviously arboreal adaptation,相反

d发现fossil证明不会爬树,不对

选e,原文中no convincing analysis


题目讨论 2条评论)

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    Jasontravelling

    Perhaps some of them could climb trees
    perhaps+could说明uncertain
    0 0 回复 2018-08-22 15:16:41
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    清澈眼中筐似海

    没有证据=不明
    0 0 回复 2018-08-19 19:55:39
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