海洋沉积物中浮游生物的这种变化标志着白垩纪和第三纪的分界线。
This change in plankton found in marine deposits is what marks the boundary between the Cretaceous and the Tertiary.
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。
“The fossil record continues to show that the origin of modern placental mammals postdates or is at the Cretaceous-Paleogene boundary, ” he said.
它说明了虱子的历史非常久，在白垩纪-早第三纪过渡期之前，而且也肯定是寄生在某种生物上的。
It says lice are old, predate the Cretaceous-Paleogene boundary, and must have been living on something.
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