Cetaceans reduce the number of breaths they take during rest periods.

鲸类动物在休息时减少它们的呼吸次数.

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It is not clear whether cetaceans undergo dream sleep.

鲸类动物是否经历梦睡眠还不清楚.

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Any of various similar cetaceans, such as the killer whale.

须鲸类;露脊鲸;长须鲸; 蓝鲸;座头鲸.

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Although limited to a skull , the Pakicetus fossil provides precious details on the origins of cetaceans.

尽管只是个头盖骨, 但它却提供了研究原始鲸类动物起源的珍贵信息.

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Missing until recently were fossils clearly intermediate, or transitional, between land cetaceans.

近期发现的化石已经可以很清晰地帮助人们了解这个问题, 以及他们之间的过渡关系.

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