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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  52
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] According to the passage, the skeleton of a pterosaur can be distinguished from that of a bird by the
选项 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.
E、location of the shoulder joint joining the wing to its body.
答案 C
解析 翼龙骨架和鸟的骨架的区别之处在于：A．翅膀大小。不足以作证据，各种类型飞行翅膀都有大有小。B．两者都有中空的骨头。同上。C．翅膀支架的解剖学来源。正确。一个第四指，一个第二指。D．后爪有钩一样结构。翼龙无此结构。E．肩关节和翅膀连接之部位。无。
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