In the fish world, too, there is an effective selection in the
course of the Cretaceous. All the fishes of modern times, except
the large family of the sharks, rays, skates, and dog-fishes
(Elasmobranchs), the sturgeon and chimaera, the mud-fishes, and a
very few other types, are Teleosts, or bony-framed fishes--the
others having cartilaginous frames. None of the Teleosts had
appeared until the end of the Jurassic. They now, like the
flowering plants on land, not only herald the new age, but
rapidly oust the other fishes, except the unconquerable shark.
They gradually approach the familiar types of Teleosts, so that
we may say that before the end of the Cretaceous the waters
swarmed with primitive and patriarchal cod, salmon, herring,
perch, pike, bream, eels, and other fishes. Some of them grew to
an enormous size. The Portheus, an American pike, seems to have
been about eight feet long; and the activity of an eight-foot
pike may be left to the angler's imagination. All, however, are,
as evolution demands, of a generalised and unfamiliar type: the
material out of which our fishes will be evolved.
Of the insects we have very little trace in the Cretaceous.
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