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 ichthyosayurs had suffered the bends before they died, but not a single Triassic specimen(标本)showed evidence of that sort of injury.

　　If ichthyosaurs did evolve an antidecompression 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.

　　Whales that suffer the bends often do so because they have surfaced to escape a predator (捕食动物)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 sharkand crocodilefree. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey(猎物)as well as predator—and often had to make a speedy exit as a result.

　　文章大意：当下潜者突然浮出水面，血液中的氮气会突然释放出来，引起剧烈的疼痛和身体的弯曲。Bruce Rothschild研究为什么普遍存在的这种现象在早期鱼龙身上不存在，晚期的鱼龙身上就出现了。

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