“The fossil record continues to show that the origin of modern placental mammals postdates or is at the Cretaceous-Paleogene boundary, ” he said.

他说：“化石记录一再证实现代胎盘类哺乳动物的起源是在白垩纪-早第三纪分界点的时候或那之后。

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The question is one of the most hotly contested in palaeontology and revolves around an apparent gap in the fossil record immediately prior to the K-T boundary - the distinct layer of geological sediments separating the Cretaceous and Tertiary periods, and associated with a massive asteroid impact and global extinction event.

BBC: Closing the 'three metre gap'