• Period: 252 BCE to 208 BCE


    Archosaurs dominated on land as dinosaurs, in the oceans as ichthyosaurs and notosaurs, and in the sky as pterosaurs. The cynodonts get smaller and more and more resemble a mammal. The first mammals and the order crocodilia appear. Plants of the genus Dicroidium were common on land. Many large aquatic amphibians temnospondyls. Extremely common ceratitic ammonoids. Modern corals and bony fish (teleosts) appear, as well as many of the modern clades of insects.
  • Period: 250 BCE to 66 BCE

    Mesozoic era

    This era is like the era of reptiles because was the dominant group of vertebrates in the earth and in the seas and the oceans. The Mesozoic lasted between 250 and 66 million years ago, and during that time the great reptiles known as dinosaurs had their heyday.
  • Period: 201 BCE to 152 BCE


    Gymnosperms (especially conifers, Bennettitales, and cycads) and ferns are common. Many types of dinosaurs, such as sauropods, carnosaurs, and stegosaurs. Mammals are common but small. First birds and lizards. Ichthyosaurs and plesiosaurs diversify. Bivalves, ammonites, and belemnites abound. Sea urchins are very common, along with crinoids, starfish, sponges, and terebratulid and corner-bellied brachiopods. Rupture of Pangea in Gondwana and Laurasia.
  • Period: 145 BCE to 72 BCE


    Flowering plants and new types of insects proliferate. More modern teleost fish are beginning to appear. Ammonites, belemnites, rudist bivalves, echinoids, and sponges are common. Various types of dinosaurs evolved on land, as well as modern crocodiles; Modern mosasaurs, pliosaurs and sharks appeared in the sea. Early birds gradually replaced pterosaurs. Monotremes, marsupials and placental mammals appeared. Gondwana Rupture.