Answer:
C. The organisms that formed them likely also lived during the Paleozoic era.
Explanation:
The organism which was found by the scientist in the same rock layer indicates that the organism was present in the same Paleozoic era where trilobites were present because both organisms found in the same rock layer. Paleozoic era was present 542 million years ago and ended into 251 million years ago. At that time, great change occurs on the Earth. In this era, plants were spreading across the earth surface and first vertebrates species start colonized.