The sharks with
crushing teeth diminish in number, and the sharp-toothed modern
shark attains the supremacy in its class, and evolves into forms
far more terrible than any that we know to-day. Skates and rays
of a more or less modern type, and ancestral gar-pikes and
sturgeons, enter the arena. But the most interesting new
departure is the first appearance, in the Jurassic, of
bony-framed fishes (Teleosts). Their superiority in organisation
soon makes itself felt, and they enter upon the rapid evolution
which will, by the next period, give them the first place in the
fish world.
Over the whole Mesozoic world, therefore, we find advance and the
promise of greater advance. The Permian stress has selected the
fittest types to survive from the older order; the Jurassic
luxuriance is permitting a fresh and varied expansion of life, in
preparation for the next great annihilation of the less fit and
selection of the more fit. Life pauses before another leap. The
Mesozoic earth--to apply to it the phrase which a geologist has
given to its opening phase--welcomes the coming and speeds the
parting guest. In the depths of the ocean a new movement is
preparing, but we have yet to study the highest forms of Mesozoic
life before we come to the Cretaceous disturbances.
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