英语翻译

题目

英语翻译
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 shark- and crocodile-free.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.】
请分析【】里的句子结构,我觉得很乱,然后标准翻译一下,

答案

第1句：主语：triassic oceans谓语动词：were （是个系动词）表语：shark-and crocodile-free状语：mercifully插入语：by contrast （不作句子的成份）第2句：状语：in the Triassic状语：then主语：ichthyosaurs谓...