Geological time scale, illustration. The globes show the configuration of the continents during the early Paleozoic (520 million years ago), late Paleozoic Era (275 million years ago), the late Mesozoic Era (65 million years ago) and today, during the Cenozoic Era. A trilobite marine arthropod represents the fauna of the early Paleozoic. Representing the fauna of the late Paleozoic is a Dimetrodon, which was a synapsid, an early form of the evolution from reptiles to mammals. Representing the fauna of the late Mesozoic is a bipedal dinosaur. A human is at right.