Modern naturalists have been pretty generally agreed that the
_Pterosaurs_ should be regarded as a peculiar group of the Reptiles;
though they have been and are still regarded by high authorities,
like Professor Seeley, as being really referable to the Birds, or
as forming a class by themselves. The chief points which separate
them from Birds, as a class, are the character of the apparatus
of flight, the entirely different structure of the fore-limb, the
absence of feathers, the composition of the tail out of distinct
vertebrae, and the general presence of conical teeth sunk in distinct
sockets in the jaws. The gap between the Pterosaurs and the Birds
has, however, been greatly lessened of late by the discovery
of fossil animals (_Ichthyornis_ and _Hesperornis_) with the
skeleton proper to Birds combined with the presence of teeth
in the jaws, and by the still more recent discovery of other
fossil animals (_Pteranodon_) with a Pterosaurian skeleton, but
without teeth; whilst the undoubtedly feathered _Archoeopteryx_
possessed a long tail composed of separate vertebrae. Upon the
whole, therefore, the relationships of the Pterosaurs cannot
be regarded as absolutely settled. It seems certain, however,
that they did not possess feathers--this implying that they were
cold-blooded animals; and their affinities with Reptiles in this,
as in other characters, are too strong to be overlooked.
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