We shall, however, find them much advanced in the
next period, and must conclude that the selection acted very
effectively among their thousand Carboniferous species.
The most interesting outcome of the new conditions is the rise
and spread of the reptiles. No other sign of the times indicates
so clearly the dawn of a new era as the appearance of these
primitive, clumsy reptiles, which now begin to oust the Amphibia.
The long reign of aquatic life is over; the ensign of progress
passes to the land animals. The half-terrestrial, half-aquatic
Amphibian deserts the water entirely (in one or more of its
branches), and a new and fateful dynasty is founded. Although
many of the reptiles will return to the water, when the land
sinks once more, the type of the terrestrial quadruped is now
fully evolved, and from its early reptilian form will emerge the
lords of the air and the lords of the land, the birds and the
mammals.
To the uninformed it may seem that no very great advance is made
when the reptile is evolved from the Amphibian. In reality the
change implies a profound modification of the frame and life of
the vertebrate. Partly, we may suppose, on account of the
purification of the air, partly on account of the decrease in
water surface, the gills are now entirely discarded.
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