The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such recurrent extinction episodes.

在这一系列周期性物种灭绝事件里，白垩纪晚期恐龙和菊石的灭绝仅仅是其中一个比较严重的事件。

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Ammonoids, with their tightly coiled, spiral shells, are also widespread in the Permian fossil record.

鹦鹉螺化石，这些螺旋状的贝壳，经常分布在二叠纪的化石群中。

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Then Whiteside and Ward looked at the fossil record of ammonoids, a class of creatures that resemble shelled squid and dominated Earth's oceans from 400 million to 65 million years ago.

怀特塞德和沃德也研究了菊石的化石记录。菊石室一种类似于鱿鱼的生物，四亿至五亿年之前菊石遍布地球海洋之中。

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