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The fossil remains of the first flying vertebrates, the pterosaurs, have intrigued paleontologists for more than two centuries. How such large creatures, which weighed in some cases as much as a piloted hang-glider and had wingspans from 8 to 12 meters, solved the problems of powered flight, and exactly what these creatures were — reptiles or birds — are among the questions scientists have puzzled over.

Perhaps the least controversial assertion about the pterosaurs is that they were reptiles. Their skulls, pelvises, and hind feet are reptilian. The anatomy of their wings suggests that they did not evolve into the class of birds. In pterosaurs a greatly elongated fourth finger of each forelimb supported a winglike membrane. The other fingers were short and reptilian, with sharpclaws. In birds the second finger is the principal strut of the wing, which consists primarily of feathers. If the pterosaurs walked on all fours, the three short fingers may have been employed for grasping. When a pterosaur walked or remained stationary, the fourth finger, and with it the wing, could only turn upward in an extended inverted V shape along each side of the animal’s body.

The pterosaurs resembled both birds and bats in their overall structure and proportions. This is not surprising because the design of any flying vertebrate is subject to aerodynamic constraints. Both the pterosaurs and the birds have hollow bones, a feature that represents a savings in weight. In the birds, however, these bones are reinforced more massively by internal struts.

Although scales typically cover reptiles, the pterosaurs probably had hairy coats. T. H. Huxley reasoned that flying vertebrates must have been warm-blooded because flying implies a high rate of metabolism, which in turn implies a high internal temperature. Huxley speculated that a coat of hair would insulate against loss of body heat and might streamline the body to reduce drag in flight. The recent discovery of a pterosaur specimen covered in long, dense, and relatively thick hairlike fossil material was the first clear evidence that his reasoning was correct.

Efforts to explain how the pterosaurs became airborne have led to suggestions that they launched themselves by jumping from cliffs, by dropping from trees, or even by rising into light winds from the crests of waves. Each hypothesis has its difficulties. The first wrongly assumes that the pterosaurs’ hind feet resembled a bat’s and could serve as hooks by which the animal could hang in preparation for flight. The second hypothesis seems unlikely because large pterosaurs could not have landed in trees without damaging their wings. The third calls for high waves to channel updrafts. The wind that made such waves however, might have been too strong for the pterosaurs to control their flight once airborne.

1. It can be inferred from the text that scientist now generally agree that the

[A] enormous wingspan of the pterosaurs enabled them to fly great distances.

[B] structure of the skeleton of the pterosaurs suggests a close evolutionary relationship to bats.

[C] fossil remains of the pterosaurs reveal how they solved the problem of powered flight.

[D] pterosaurs were reptiles.

2. The author views the idea that the pterosaurs became airborne by rising into light winds created by waves as

[A] revolutionary.

[B] unlikely.

[C] unassailable.

[D] probable.

3. According to the text, the skeleton of a pterosaur can be distinguished from that of a bird by the

[A] size of its wingspan.

[B] presence of hollow spaces in its bones.

[C] anatomic origin of its wing strut.

[D] presence of hooklike projections on its hind feet.

4. The ideas attributed to T. H. Huxley in the text suggest that he would most likely agree with which of the following statements?

[A] An animal’s brain size has little bearing on its ability to master complex behaviors.

[B] An animal’s appearance is often influenced by environmental requirements and physical capabilities.

[C] Animals within a given family group are unlikely to change their appearance dramatically over a period of time.

[D] The origin of flight in vertebrates was an accidental development rather than the outcome of specialization or adaptation.

5. Which of the following best describes the organization of the last paragraph of the text?

[A] New evidence is introduced to support a traditional point of view.

[B] Three explanations for a phenomenon are presented and each is disputed by means of specific information.

[C] Three hypotheses are outlined and evidence supporting each is given.

[D] Recent discoveries are described and their implications for future study are projected.

[答案與考點解析]

1. 【答案】D

【考點解析】這是一道審題定位題型。該題的答案信息在第二段的第一句，根據(jù)本句的內(nèi)容即可得出本題的正確答案是D?？忌訌妼︻}干的理解和認識，并且要善于找到原文和題干相吻合之處，否則就會失去解題思路。

2. 【答案】B

【考點解析】本題是一道句間關(guān)系題型。本題的答案信息在尾段的第一、二句和尾段的倒數(shù)第一、二句。從尾段的第二句 “Each hypothesis has its difficulties” (每種假設都有缺陷)可以判斷：作者認為“從浪尖上伴輕風飛起”是不可能的?？忌訌妼渥又g語意關(guān)系的理解。

3. 【答案】C

【考點解析】本題是一道審題定位題。其答案信息在第三段。題干中問翼龍和鳥類骨骼方面的“不同”。原文第三段中涉及兩者相同與不同。第三段的尾句暗示本題的正確答案是C?？忌诮忸}時應加強審題定位的能力。

4. 【答案】B

【考點解析】這是一道歸納推導題。本題的正確答案在第四段的第一、二、三句。這三句話的內(nèi)容暗示本題的正確答案是B，即動物的外型通常受環(huán)境要求和生理能力的影響。考生在解題時應注意提高對原文信息的歸納推導能力。

5. 【答案】B

【考點解析】本題是一道段落結(jié)構(gòu)識別題。尾段的第一句對所談現(xiàn)象提出了三種解釋，然后針對每一種解釋進行科學上的否定?？梢姳绢}的正確答案是B。考生在復習中應該加強對段落結(jié)構(gòu)的識別能力。

[參考譯文]

第一批會飛的脊椎動物——翼龍的化石，已經(jīng)讓古生物學家感興趣達兩個多世紀了。這種有時和大型滑翔機一樣重，而且翅膀展開達8—12米寬的龐然大物是如何克服飛行時的重力，以及這種生物到底是屬于鳥類還是爬行動物，對科學家們來講仍舊是個謎。

可能，最少引起爭論的意見就是翼龍是爬行動物。它們的頭蓋骨、骨盆以及后腿都是爬行動物類型。對它們翅膀的解剖學研究證明它們尚未進化為鳥。翼龍每個前肢的大大延長的第四指支撐一個翅膀狀的薄膜，其它指頭小，而且是典型的爬行動物式，有尖爪。而鳥類的第二指進化成為翅膀的主要支架，翅膀也主要是羽毛構(gòu)成的。當翼龍四肢爬行時，其它指可以用來抓取。而當它行走或不動時，第四指，連同翅膀，只能向上伸展，在身體兩側(cè)呈倒轉(zhuǎn)的V字型。

翼龍和鳥類以及蝙蝠在總體結(jié)構(gòu)及比例上很相似。這并不奇怪，因為任何飛翔脊椎動物都要受空氣動力的約束。翼龍和鳥都有中空的骨頭，這是為了節(jié)省重量。不過在鳥類中，這種骨頭受內(nèi)部支柱影響，重量大大增加。

盡管爬行動物通常全身鱗片，翼龍卻可能擁有毛發(fā)。赫胥黎對此解釋說，飛翔脊椎動物肯定已經(jīng)是熱血動物，因為飛翔要求一個高新陳代謝率，后者要求一個較高的體溫。赫氏設想一層毛發(fā)覆蓋物可以隔絕身體熱量的損失，從而使身體在減輕飛行重量方面更為有效。最近一些有又長又密且厚的毛發(fā)的翼龍化石的發(fā)現(xiàn)，終于明白無誤地證明赫氏的觀點是對的。

解釋翼龍怎樣起飛的努力產(chǎn)生以下設想：它們從懸崖上起跳，或從樹上起跳或者甚至從浪尖上伴輕風飛起。每種假設都有缺陷。第一種錯誤地設想翼龍的后爪象蝙蝠一樣，鉤子似的掛著為飛行做準備。第二種看來也不可能，因為大型翼龍不可能降在樹上而不傷害它們的翅膀。第三種假設必須要有高浪來形成上升氣流才能實現(xiàn)。然而，能產(chǎn)生此種大浪的風可能對翼龍來說過于猛烈，以至于它一旦升空，就無法控制自己。

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（責任編輯：rhj）

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