and interesting reptiles we see in the Zoo, the crocodile and
its cousin, the alligator. In the everglades of Florida both are found.
The crocodile of the Nile is protected by popular superstition, so it is
in better luck than ours. The alligators have been killed off for their
skins, and it is only a matter of time till these lumbering creatures
will be found only in places where they are protected as the remnants of
a vanished race. Giant reptiles of other kinds are few upon the earth
now. The _boa constrictor_ is the giant among snakes. The great tropical
turtles represent an allied group. Most of the turtles, lizards, and
snakes are small, and in no sense dominant over other creatures.

The rocks that lie among the coal measures contain fossils of huge
animals that lived in fresh water and on land, the ancestors of our
frogs, toads, and salamanders, a group we call amphibians. Some of these
animals had the form of snakes; some were fishlike, with scaly bodies;
others were lizard-like or like huge crocodiles. These were the
ancestors of the reptiles, which became the rulers of land and sea
during the Mesozoic Era. The rocks that overlie the coal measures
contain fossils of these gigantic animals.

Strange crocodile-like reptiles, with turtle-like beaks and tusks, but
no teeth, left their skeletons in the mud of the shores they frequented.
And others had teeth in groups--grinders, tearers, and cutters--like
mammals. These had other traits like the old-fashioned, egg-laying
mammals, the duck-billed platypus, for example, that is still found in
Australia. Along with the remains of these creatures are found small
pouched mammals, of the kangaroo kind, in the rocks of Europe and
America. These land animals saw squatty cycads, and cone-bearing trees,
the ancestors of our evergreens, growing in forests, and marshes covered
with luxuriant growths of tree ferns and horsetails, the fallen bodies
of which formed the recent coal that is now dug in Virginia and North
Carolina. Ammonites, giant sea snails, with chambered shells that
reached a yard and more in diameter, and gigantic squids, swam the seas.
Sea urchins, starfish, and oysters were abundant. Insects flitted
through the air, but no birds appeared among the trees or beasts in the
jungles. Over all forms of living creatures reptiles ruled. They were
remarkable in size and numbers. There were swimming, running, and flying
forms.

[Illustration: Banded sandstone from Cal