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If a diver surfaces too quickly, he may suffer the bends. Nitrogen dissolved in his blood is suddenly liberated by the reduction of pressure. The consequence, if the bubbles accumulate in a joint, is sharp pain and abent body—thus the name. If the bubbles form in his lungs or his brain, the consequence can be death.
如果潜水员浮出水面太快，他可能会得减压病（bend，原意为弯曲）。溶解在血液里的氮气因为气压下降而突然释放，如果气泡聚积在关节部位，就会剧痛，直不起腰——减压病因此得名；如果气泡形成于肺部或者大脑，可能导致死亡。
Other air-breathing animals also suffer this decompression sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil bones that have caved in on themselves are thus a sign that the animal once had the bends.
其他呼吸空气的动物如果浮出水面太快也会得减压病：例如鲸鱼。很久以前，鱼龙也是如此。从这些古代海洋动物的骨骼可以看出它们得过减压病。如果氮气气泡形成于骨骼内，就会切断血液供应。这会杀死骨细胞，弱化骨骼，有时甚至发生断裂。因此存在塌陷骨骼的化石是这种动物曾经得过减压病的标志。
Bruce Rothschild of the University of Kansas knewall this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past. What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years. To this end, he and his colleagues traveled the world’s natural-history museums, looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods.
勘萨斯大学的布鲁斯·罗斯柴尔德在开始对鱼龙骨骼研究时发现这一问题在过去非常普遍。他特别想知道鱼龙在1.5亿年里如何适应减压。为此，他和同事们参观了世界自然历史博物馆，观察了三叠纪、侏罗纪晚期和白垩纪的数百条鱼龙。
When he started, he assumed that signs of the bends would be rarer in younger fossils, reflecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died, but not a single Triassic specimen showed evidence of that sort of injury.
刚开始他认为得减压病的标志在较新的化石中会更为少见，这反映了它们在适应减压问题上的逐渐演化。然而，他惊讶地发现情况恰恰相反。超过15%的侏罗纪和白垩纪鱼龙在死亡前得过减压病，但三叠纪的标本却没有证据表明有过这种伤害。
If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, most strangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened. He suspects it was evolution in other animals that caused the change.
如果鱼龙真的进化出一种对抗减压的方式，显然进化如此之快——但最奇怪的是，它们后来失去了这种能力。罗斯柴尔德博士认为情况并非如此，他怀疑是其他动物的进化导致了这种变化。
Whales that suffer the bends often do so because they have surfaced to escape a predator such as a large shark. One of the features of Jurassic oceans was an abundance of large sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, by contrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey as well as predator—and often had to make a speedy exit as a result.
得减压病的鲸鱼经常快速浮出水面，它们是为了躲避捕食者，比如大型鲨鱼。侏罗纪海洋的特征之一是拥有大量的大型鲨鱼和鳄鱼，它们都喜欢以鱼龙作为午餐。而幸运的是，三叠纪的海洋没有鲨鱼和鳄鱼。在三叠纪，鱼龙是食物链的顶端。在侏罗纪和白垩纪，它们是猎物，也是捕食者，因此经常不得不迅速离开。
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