The Cenozoic and Paleozoic ERAS are two of the major divisions of geologic time. The Cenozoic era began about 65 million years ago and is marked by the emergence of modern mammals, birds, and flowering plants. The Paleozoic era began about 541 million years ago and is marked by the emergence of the first complex life forms, including fish, amphibians, and reptiles. The answer to the crossword puzzle is ERAS, which is an acronym for these two ERAS.