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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  88
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 which of the following is characteristic of the pterosaurs?
选项 A、They were unable to fold their wings when not in use.
B、They hung upside down from branches as bats do before flight.
C、They flew in order to capture prey.
D、They were an early stage in the evolution of the birds.
E、They lived primarily in a forest-like habitat.
答案 A
解析 下列哪一个是翼龙的特点?A．不用翅膀时不能折叠。正确。原文L27～32讲到它们不用翅膀时，只能使之成为倒V字型。折叠翅膀是鸟类的特点。B．飞前像蝙蝠那样倒挂。文中L64—69对此加以否认。C．它们飞行是为了捕食。无。D．是鸟类进化的早期阶段。文中明确说它们属爬行动物。E．主要在类似森林的环境中居住。文中第三段L69—72对第二个假设“它们在树上起飞降落”已经否定，所以不可能在森林环境中居住。
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