The Mesozoic opens in the middle of the great revolution
described in the last chapter. Its first section, the Triassic
period, is at first a mere continuation of the Permian. A few
hundred species of animals and hardy plants are scattered over a
relatively bleak and inhospitable globe. Then the land begins to
sink once more. The seas spread in great arms over the revelled
continents, the plant world rejoices in the increasing warmth and
moisture, and the animals increase in number and variety. We pass
into the Jurassic period under conditions of great geniality.
Warm seas are found as far north and south as our present polar
regions, and the low-lying fertile lands are covered again with
rich, if less gigantic, forests, in which hordes of stupendous
animals find ample nourishment. The mammal and the bird are
already on the stage, but their warm coats and warm blood offer
no advantage in that perennial summer, and they await in
obscurity the end of the golden age of the reptiles. At the end
of the Jurassic the land begins to rise once more. The warm,
shallow seas drain off into the deep oceans, and the moist,
swampy lands are dried.
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