The eyes, again, which
may in the larger animals be fifteen inches in diameter, are
protected by a circle of radiating bony plates. In fine, the
discovery of young developed skeletons inside the adult frames
has taught us that the Ichthgosaur had become viviparous, like
the mammal. Cutting its last connection with the land, on which
it originated it ceased to lay eggs, and developed the young
within its body.
The Ichthyosaur came of the reptile group which we have called
the Diapsids. The Plesiosaur seems to belong to the Synapsid
branch. In the earlier Mesozoic we find partially aquatic
representatives of the line, like the Nothosaur, and in the later
Plesiosaur the adaptation to a marine life is complete. The skin
has lost its scales, and the front limbs are developed into
powerful paddles, sometimes six feet in length. The neck is drawn
out until, in some specimens, it is found to consist of
seventy-six vertebrae: the longest neck in the animal world. It
is now doubted, however, if the neck was very flexible, and, as
the jaws were imperfectly joined, the common picture of the
Plesiosaur darting its snake-like neck in all directions to seize
its prey is probably wrong.
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