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。
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.
无齿翼龙生活在6000万年前，这个时候是白垩纪晚期。
Pteranodons lived 60 million years ago. That time was called the late Cretaceous period.
鸟是一种已经灭绝的不会飞翔的水鸟，生活在白垩纪晚期。
Hesperornis is an extinct genus of flightless aquatic birds that lived during the Late Cretaceous.
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