t joints,
and the heads were movable. In these two particulars the fishes
resembled reptiles. The modern gar-pike has a number of the same
characteristics.

Another backboned creature of the ancient seas was the ancestral type of
the shark family. In some points this old-fashioned shark reminds us of
birds and turtles. These early fishes foreshadowed all later
vertebrates, not yet on the earth. After them came the amphibians, then
the reptiles, then the birds, and latest the mammals.

The race of fishes began, no doubt, with forms so soft-boned that no
fossil traces are preserved in the rocks. When those with harder bones
appeared, the fossil record began, and it tells the story of the passing
of the early, unfish-like forms, and the coming of new kinds, great in
size and in numbers, that swarmed in the seas, and were tyrants over all
other living things. They conquered the giant straight-horns and
trilobites, former rulers of the seas.

[Illustration: _By permission of the American Museum of Natural History_

A sixteen-foot fossil fish from Cretaceous of Kansas, with a modern
tarpon]

[Illustration: _By permission of the American Museum of Natural History_

Canon Diablo meteorite from Arizona]

One of these giant fishes fifteen to twenty feet long, three feet wide,
had jaws two feet long, set with blade-like teeth. Devonian rocks in
Ohio have yielded fine fossils of gigantic fishes and sharks.

Devonian fishes were unlike modern kinds in these particulars, the
spinal column extended to the end of the tail, whether the fins were
arranged equally or unequally on the sides; the paired side fins look
like limbs fringed with fins. Every Devonian fish of the gar type seems
to have had a lung to help out its gill-breathing.

In these traits the first fishes were much like the amphibians. They
were the parent stock from which branched later the true fishes and the
amphibians, as a single trunk parts into two main boughs. The trunk is
the connecting link.

The sea bottom was still thronged with crinoids, and lamp shells, and
cup corals. Shells of both clam and snail shapes are plentiful. The
chambered straight-horns are fewer and smaller, and coiled forms of this
type of shell are found. Trilobite forms are smaller, and their numbers
decrease.

The first land plants appeared during this age. Ferns and giant club
mosses and cycads grew in swampy ground. This was the beginning of the
wonderful fern forests that mark