The reptiles then appeared and gained ascendancy over the amphibia, to
become in the Mesozoic age the highest and most varied of the existing
vertebrates. At that time there were the great land dinosaurs with a
length of 80 feet, like _Brontosaurus_; aquatic forms like _Ichthyosaurus_
and _Plesiosaurus_, whose mode of evolution from terrestrial to swimming
habits was like that of seals and penguins of far later eras. Flying
reptiles also evolved, to set an example for the bats of the mammalian
class, for both kinds of flying organisms converted their anterior limbs
into wings, although in different ways.
During the Triassic and Jurassic periods of the Mesozoic age, the first
birds and mammals appeared to follow out their diverging and independent
lines of descent. Palaeontology makes it possible to trace the origin and
development of many of the different branches that grew out of the
mammalian limb from different places and at different times during the
Mesozoic and the following age, called the Cenozoic, or age of recent
animals. It is unnecessary, however, for us to review more of the details:
the main result is obvious; namely, that the appearance of the great
classes of vertebrates is in the order of comparative anatomy and
embryology.
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