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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. 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.
3. 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.
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]
1. D
2. C
3. B
4. B
5. B
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