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第一段
1 .Recent research has revealed the pterosaurs may in fact have been capable of powered flight.
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第二段
1 .First, the issue of pterosaur metabolism.
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2 .Some recently discovered pterosaur fossils indicate that pterosaurs had a dense, hair-like covering, somewhat similar to fur.
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3 .Hair or fur covering is typical of warm-blooded animals because those animals need to maintain a high body temperature when external conditions are cold.
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4 .So if the metabolism of pterosaurs was more like that of warm-blooded animals and so faster than the reading suggests, then it would have supplied them with the energy needed for powered flight.
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第三段
1 .Second, the idea that large pterosaurs couldn't use powered flight because they were too heavy.
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2 .We now know that pterosaurs had anatomical features that made them unusually light for their size.
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3 .For example, the bones of pterosaurs were hollow instead of solid.
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4 .Hollow, light-weight bones would have kept the pterosaurs weight low despite their large body frames.
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5 .The pterosaurs' weight was probably low enough to allow them to keep themselves airborne by flapping their wings.
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第四段
1 .Third, takeoff would indeed be a problem for pterosaurs if they took off the way birds do.
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2 .But there are important differences between birds and pterosaurs.
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3 .Birds only use their hind limbs, their legs, for walking on the ground.
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4 .So they only have two limbs to push off from when they launch.
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5 .But pterosaurs walked on all four limbs while on the ground.
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6 .There are modern flying animals that walk on all four limbs.
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7 .Bats, for example.
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8 .And they use all four limbs to push off the ground, not just the back ones.
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9 .Studies indicate that even the largest pterosaurs would have had no trouble using all four limbs to run fast enough or jump high enough to launch themselves into the air.
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