[Illustration: Fig. 179--_Rhamphorhynchus Bucklandi_, restored.
Bath Oolite, England. (After the late Professor Phillips.)]
The _Pterosaurs_ are wholly Mesozoic, ranging from the Lias to
the Chalk inclusive; and the fine-grained Lithographic Slate of
Solenhofen has proved to be singularly rich in their remains.
The genus _Pterodactylus_ itself has the jaws toothed to the
extremities with equal-sized conical teeth, and its species range
from the Middle Oolites to the Cretaceous series, in connection
with which they will be again noticed, together with the toothless
genus _Pteranodon_. The genus _Dimorphodon_ is Liassic, and is
characterised by having the front teeth long and pointed, whilst
the hinder teeth are small and lancet-shaped. Lastly, the singular
genus _Rhamphorhynchus_, also from the Lower Oolites, is
distinguished by the fact that there are teeth present in the
hinder portions of both jaws; but the front portions are toothless,
and may have constituted a horny beak. Like most of the other
Jurassic Pterosaurs, _Rhamphorhynchus_ (fig. 179) does not seem
to have been much bigger than a pigeon, in this respect falling
far below the giant "Dragons" of the Cretaceous period. It differed
from its relatives, not only in the armature of the mouth, but
also in the fact that the tail was of considerable length.
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