153), forming broad crushing
plates adapted for the comminution of shell-fish. There is a
row of these teeth all round the upper jaw proper, and a double
series on the palate, but the lower jaw has only a single row of
teeth. _Placodus_ is found in the Muschelkalk, and the characters
of its dental apparatus indicate that it was much more peaceful
in its habits than its associates the Nothosaur and Simosaur.
[Illustration: Fig. 153.--Under surface of the upper jaw and palate
of _Placodus gigas_. Muschelkalk, Germany.]
The Triassic rocks of South Africa and India have yielded the
remains of some extraordinary Reptiles, which have been placed by
Professor Owen in a separate order under the name of _Anomodontia_.
The two principal genera of this group are _Dicynodon_ and
_Oudenodon_, both of which appear to have been large Reptiles,
with well-developed limbs, organised for progression upon the
dry land. In _Oudenodon_ (fig. 154, B) the jaws seem to have
been wholly destitute of teeth, and must have been encased in
a horny sheath, similar to that with which we are familiar in
the beak of a Turtle. In _Dicynodon_ (fig. 154, A), on the other
hand, the front of the upper jaw and the whole of the lower jaw
were destitute of teeth, and the front of the mouth must have
constituted a kind of beak; but the upper jaw possessed on each
side a single huge conical tusk, which is directed downwards,
and must have continued to grow during the life of the animal.
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