Jurassic Period, Interval of geologic time, 201.3–145 million years ago, that is one of the three major divisions of the Mesozoic Era. It was preceded by the Triassic Period and followed by the Cretaceous. During the Jurassic, Pangea began to break up into the present-day continents. Marine invertebrates flourished, and large reptiles dominated many marine habitats. On land, ferns, mosses, cycads, and conifers thrived, some developing flowerlike structures in place of cones. The dinosaurs rose to supremacy on land, and by the end of the Jurassic the largest species had evolved. Archaeopteryx, the first primitive bird, appeared before the end of the period. Early mammals, tiny shrewlike creatures that appeared near the close of the preceding Triassic, managed to survive and evolve.