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.
二叠纪大灭绝事件比其他大灭绝事件受到的关注要少得多，因为那时灭绝的大多是我们不熟悉的物种。
The Permian event has attracted much less attention than other mass extinctions because mostly unfamiliar species perished at that time.
人们已经得到了6500万年前白垩纪灭绝事件很好的证据。
So 65 million years ago they've got very good evidence of the cretaceous exctinction event.
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