Scientists find trilobites during a routine dig. trilobites were common in the paleozoic era (540 to 245 million years ago) and went extinct during the late permian period (248 million years ago). on another site, the scientists find ammonites. ammonites lived during the mesozoic era (245 to 65 million years ago) and are not found after that period. what can be concluded about the rock layers? choose all that apply. the rock layers must have formed at the same time because they both contain biozones. the rock layers must have formed at different times because they contain two different biozones. the rock layer containing the trilobites must have formed before the one containing the ammonites. the rock layer containing the trilobites must have formed after the one containing the ammonites.