]
The Trias has also yielded the remains of the great marine reptiles
which are often spoken of collectively as the "Enaliosaurians"
or "Sea-lizards," and which will be more particularly spoken
of in treating of the Jurassic period, of which they are more
especially characteristic. In all these reptiles the limbs are
flattened out, the digits being enclosed in a continuous skin,
thus forming powerful swimming-paddles, resembling the "flippers"
of the Whales and Dolphins both in their general structure and
in function. The tail is also long, and adapted to act as a
swimming-organ; and there can be no doubt but that these
extraordinary and often colossal reptiles frequented the sea,
and only occasionally came to the land. The Triassic Enaliosaurs
belong to a group of which the later genus _Plesiosaurus_ is
the type (the _Sauropterygia_). One of the best known of the
Triassic genera is _Nothosaurus_ (fig. 152, a), in which the
neck was long and bird-like, the jaws being immensely elongated,
and carrying numerous powerful conical teeth implanted in distinct
sockets. The teeth in _Simosaurus_ (152, b) are of a similar
nature; but the orbits are of enormous size, indicating eyes of
corresponding dimensions, and perhaps pointing to the nocturnal
habits of the animal. In the singular _Placodus_, again, the
teeth are in distinct sockets, but resemble those of many fishes
in being rounded and obtuse (fig.
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