Merriam-Webster Collegiate Dictionary - paleozoic

 adjective  Date: 1838 of, relating to, originating in, or being an era of geological history that extends from the beginning of the Cambrian to the close of the Permian and is marked by the culmination of nearly all classes of invertebrates except the insects and in the later epochs by the appearance of terrestrial plants, amphibians, and reptiles; also relating to the corresponding system of rocks — see geologic time table  • ~ noun