a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found 同义词：guide fossil,
例句与用法
1.
Thus any rock found bearing these index fossils can be dated fairly accurately as belonging to their proper period in history . 因此凡是发现含有这类标准化石的岩石就可以相当精确地断定它们在地质史上属于某个相应时代。
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