Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/163

Rh the lowest of the order. The existence of such large birds as the Brontozoon, at this period, is in harmony with the view of the Reptiles being the progenitors through the Ostrich family of the Birds, while the fact of both Birds and Mammals appearing about the same time confirms the theory that they are the diverging stem of a common stock, the Reptilia.

This period is called after the Jura Mountains of Switzerland, and is remarkable for the variety of its Reptiles, which were of great size. Conspicuous were the "terrible reptiles," or Dinosauria, of which the carnivorous Megalosaurus and herbivorous Iguanodon were upwards of thirty feet long. Very curious flying Reptiles existed in the Jurassic period, such as the Pterodactyle and Dimorphodon (Fig. 150). Equally characteristic were the Ichthyosauri (Fig. 58) and Plesiosauri, upwards of thirty feet long, whose organization united reptilian with batrachian and piscine characters. Their fin- or paddle-like extremities would indicate that they had diverged from the stem of Fishes rather than from that of the Batrachia. Their structure, however, is so peculiar as to make it extremely difficult to determine their exact position in the animal kingdom. Crocodiles and Turtles appear now for the first time, together with Sharks of the cutting-teeth kind, like the modern gray Shark (Notidanus), which will soon replace the Cestracions, so striking a feature of the ancient formations, while the Insects are represented by the high order of Hymenoptera. The Compsognathus (delicate jaw), a very bird-like Reptile, and the Archeopteryx (ancient bird), a reptile-like Bird, both Jurassic fossils, are extremely interesting to the Evolutionist, as almost bridging over the gap between existing reptiles and birds. The Mammals of this period are still of the Marsupial order.