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. 如果潛水員浮出水面太快，他可能會得減壓?。╞end，原意為彎曲）。溶解在血液里的氮氣因為氣壓下降而突然釋放，如果氣泡聚積在關(guān)節(jié)部位，就會劇痛，直不起腰——減壓病因此得名；如果氣泡形成于肺部或者大腦，可能導(dǎo)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. 其他呼吸空氣的動物如果浮出水面太快也會得減壓病：例如鯨魚。很久以前，魚龍也是如此。從這些古代海洋動物的骨骼可以看出它們得過減壓病。如果氮氣氣泡形成于骨骼內(nèi)，就會切斷血液供應(yīng)。這會殺死骨細(xì)胞，弱化骨骼，有時甚至發(fā)生斷裂。因此存在塌陷骨骼的化石是這種動物曾經(jīng)得過減壓病的標(biāo)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. 勘薩斯大學(xué)的布魯斯·羅斯柴爾德在開始對魚龍骨骼研究時發(fā)現(xiàn)這一問題在過去非常普遍。他特別想知道魚龍在1.5億年里如何適應(yīng)減壓。為此，他和同事們參觀了世界自然歷史博物館，觀察了三疊紀(jì)、侏羅紀(jì)晚期和白堊紀(jì)的數(shù)百條魚龍。 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. 剛開始他認(rèn)為得減壓病的標(biāo)志在較新的化石中會更為少見，這反映了它們在適應(yīng)減壓問題上的逐漸演化。然而，他驚訝地發(fā)現(xiàn)情況恰恰相反。超過15%的侏羅紀(jì)和白堊紀(jì)魚龍在死亡前得過減壓病，但三疊紀(jì)的標(biāo)本卻沒有證據(jù)表明有過這種傷害。 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. 如果魚龍真的進(jìn)化出一種對抗減壓的方式，顯然進(jìn)化如此之快——但最奇怪的是，它們后來失去了這種能力。羅斯柴爾德博士認(rèn)為情況并非如此，他懷疑是其他動物的進(jìn)化導(dǎo)致了這種變化。 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. 得減壓病的鯨魚經(jīng)?？焖俑〕鏊?，它們是為了躲避捕食者，比如大型鯊魚。侏羅紀(jì)海洋的特征之一是擁有大量的大型鯊魚和鱷魚，它們都喜歡以魚龍作為午餐。而幸運的是，三疊紀(jì)的海洋沒有鯊魚和鱷魚。在三疊紀(jì)，魚龍是食物鏈的頂端。在侏羅紀(jì)和白堊紀(jì)，它們是獵物，也是捕食者，因此經(jīng)常不得不迅速離開。