Jurassic World Dinosaur Field Guide

The first era of visible life is called the Paleozoic (PAY-lee-o-ZO-ick), or “ancient life,” Era. This is when trilobites (an extinct group of sea-dwelling relatives of insects, crustaceans, and spiders) lived, fishes ruled the seas, and the first plants, insects, and amphibians (animals with backbones that live on land but must be in water to reproduce) colonized the planet. It was late in the Paleozoic that descendants of the amphibians developed shelled eggs, evolved, and split into the two major groups of dominant land vertebrates (backboned animals) that have ruled until today. One group is called the synapsids, which includes the mammals (humans among them) and our protomammal ancestors. The other, and far larger, group is called the reptiles. Reptiles include turtles, lizards and snakes, crocodilians, dinosaurs, birds, and various other extinct groups.