of the vegetarian Ornithopods
developed heavy armour, for defence against the carnivores, and
became, under the burden of its weight, the quadrupedal and monstrous
Stegosauria and Ceratopsia. Taking this instructive general view of the
spread of the Deinosaurs as the best interpretation of the material we
have, we may now glance at each of the orders in succession.

The Theropods varied considerably in size and agility. The Compsognathus
was a small, active, rabbit-like creature, standing about two feet high
on its hind limbs, while the Megalosaurs stretched to a length of
thirty feet, and had huge jaws armed with rows of formidable teeth. The
Ceratosaur, a seventeen-foot-long reptile, had hollow bones, and we find
this combination of lightness and strength in several members of the
group. In many respects the group points more or less significantly
toward the birds. The brain is relatively large, the neck long, and
the fore limbs might be used for grasping, but had apparently ceased to
serve as legs. Many of the Theropods were evidently leaping reptiles,
like colossal kangaroos, twenty or more feet in length when they were
erect. It is the general belief that the bird began its career as a
leaping reptile, and the feathers, or expanded scales, on the front
limbs helped at first to increase the leap. Some recent authorities
hold, however, that the ancestor of the bird was an arboreal reptile.

To the order of the Sauropods belong most of the monsters whose
discovery has attracted general attention in recent years. Feeding
on vegetal matter in the luscious swamps, and having their vast bulk
lightened by their aquatic life, they soon attained the most formidable
proportions. The admirer of the enormous skeleton of Diplodocus (which
ran to eighty feet) in the British Museum must wonder how even such
massive limbs could sustain the mountain of flesh that must have
covered those bones. It probably did not walk so firmly as the skeleton
suggests, but sprawled in the swamps or swam like a hippopotamus. But
the Diplodocus is neither the largest nor heaviest of its family. The
Brontosaur, though only sixty feet long, probably weighed twenty tons.
We have its footprints in the rocks to-day, each impression measuring
about a square yard. Generally, it is the huge thigh-bones of these
monsters that have survived, and give us an idea of their size. The
largest living elephant has a femur scarcely four feet long, but the
femur of th