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.
[答案与考点解析]
1. 【答案】D
【考点解析】这是一道审题定位题型。该题的答案信息在第二段的第一句，根据本句的内容即可得出本题的正确答案是D。考生要加强对题干的理解和认识，并且要善于找到原文和题干相吻合之处，否则就会失去解题思路。
2. 【答案】B
【考点解析】本题是一道句间关系题型。本题的答案信息在尾段的第一、二句和尾段的倒数第一、二句。从尾段的第二句 “Each hypothesis has its difficulties” (每种假设都有缺陷)可以判断：作者认为“从浪尖上伴轻风飞起”是不可能的。考生要加强对句子之间语意关系的理解。
3. 【答案】C
【考点解析】本题是一道审题定位题。其答案信息在第三段。题干中问翼龙和鸟类骨骼方面的“不同”。原文第三段中涉及两者相同与不同。第三段的尾句暗示本题的正确答案是C。考生在解题时应加强审题定位的能力。
4. 【答案】B
【考点解析】这是一道归纳推导题。本题的正确答案在第四段的第一、二、三句。这三句话的内容暗示本题的正确答案是B，即动物的外型通常受环境要求和生理能力的影响。考生在解题时应注意提高对原文信息的归纳推导能力。
5. 【答案】B
【考点解析】本题是一道段落结构识别题。尾段的第一句对所谈现象提出了三种解释，然后针对每一种解释进行科学上的否定。可见本题的正确答案是B。考生在复习中应该加强对段落结构的识别能力。
[参考译文]
第一批会飞的脊椎动物——翼龙的化石，已经让古生物学家感兴趣达两个多世纪了。这种有时和大型滑翔机一样重，而且翅膀展开达8—12米宽的庞然大物是如何克服飞行时的重力，以及这种生物到底是属于鸟类还是爬行动物，对科学家们来讲仍旧是个谜。
可能，最少引起争论的意见就是翼龙是爬行动物。它们的头盖骨、骨盆以及后腿都是爬行动物类型。对它们翅膀的解剖学研究证明它们尚未进化为鸟。翼龙每个前肢的大大延长的第四指支撑一个翅膀状的薄膜，其它指头小，而且是典型的爬行动物式，有尖爪。而鸟类的第二指进化成为翅膀的主要支架，翅膀也主要是羽毛构成的。当翼龙四肢爬行时，其它指可以用来抓取。而当它行走或不动时，第四指，连同翅膀，只能向上伸展，在身体两侧呈倒转的V字型。
翼龙和鸟类以及蝙蝠在总体结构及比例上很相似。这并不奇怪，因为任何飞翔脊椎动物都要受空气动力的约束。翼龙和鸟都有中空的骨头，这是为了节省重量。不过在鸟类中，这种骨头受内部支柱影响，重量大大增加。
尽管爬行动物通常全身鳞片，翼龙却可能拥有毛发。赫胥黎对此解释说，飞翔脊椎动物肯定已经是热血动物，因为飞翔要求一个高新陈代谢率，后者要求一个较高的体温。赫氏设想一层毛发覆盖物可以隔绝身体热量的损失，从而使身体在减轻飞行重量方面更为有效。最近一些有又长又密且厚的毛发的翼龙化石的发现，终于明白无误地证明赫氏的观点是对的。
解释翼龙怎样起飞的努力产生以下设想：它们从悬崖上起跳，或从树上起跳或者甚至从浪尖上伴轻风飞起。每种假设都有缺陷。第一种错误地设想翼龙的后爪象蝙蝠一样，钩子似的挂着为飞行做准备。第二种看来也不可能，因为大型翼龙不可能降在树上而不伤害它们的翅膀。第三种假设必须要有高浪来形成上升气流才能实现。然而，能产生此种大浪的风可能对翼龙来说过于猛烈，以至于它一旦升空，就无法控制自己。
