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  3. The fossil remains of the first flying vertebrates, the pterosaurs, have int

The fossil remains of the first flying vertebrates, the pterosaurs, have int

游客2024-01-13  58
问题     The fossil remains of the first flying vertebrates, the pterosaurs, have intrigued paleontologists lor more than two centuries. How such large crea- tures, 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 sharp claws. 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 warmblooded because flying implies a high rate of metabolism, which in turn implies a high internal temperature. Hux- ley 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 un- likely 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. [br] It can be inferred from the passage that scientists now generally agree that the
选项 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.
E、pterosaurs walked on all fours.
答案 D
解析 科学家们大致同意的一点是：原文L12指出，科学家们争论最少的一点，即为本题所问。A．大型翅膀使翼龙能飞很远距离。无。B．翼龙骨架显示它们和蝙蝠亲缘相近。此点原文L35—40明确说，是适应飞行条件而形成的。不能说明亲缘关系。C．化石遗物揭示了它们怎样进行负重飞行。从原文最后一段可知，虽提供了多种假设，但都有缺陷。D．翼龙是爬行动物。正确，符合L12一14的叙述。E．翼龙四脚行进。在原文L24—25，并不是作者论述重点，也未指出在此点上科学家有一致意见。
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