GEOLOG Y. 119 
the lowest ofthe 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. 
E JURASSIC PERIOD. 
This period is called after the Jura Mountains of Swit- 
zerland, 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 Megalo- 
saurus 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 forma- 
tions, 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. 
