Final answer:
The Tethyan Seaway was most prominently in existence during the Mesozoic era, which followed after the Paleozoic era.
Step-by-step explanation:
The Tethyan Seaway was most prominent during the Mesozoic era. The Paleozoic era, on the other hand, was characterized by the formation and existence of supercontinents like Gondwana and Laurentia. By the end of the Paleozoic, Pangea had begun to form.
The Tethyan Seaway, a major body of water that existed between Gondwana and Laurasia during the Mesozoic era, allowed for the passage of marine life and significantly influenced the deposition of sedimentary rock that would later be of interest in the study of petroleum systems.