THE JURASSIC PERIOD. 247 
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 struc- 
ture of the fore-limb, the absence of feathers, the composition 
of the tail out of distinct vertebre, 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 
(Lchthyornis 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 (/¢evanodon) 
with a Pterosaurian skeleton, but without teeth ; whilst the un- 
doubtedly feathered Archeopteryx possessed a long tail com- 
posed of separate vertebree. 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. 
The Prerosaurs 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 Prerodactylus itself has the jaws toothed to the ex- 
tremities with equal-sized conical teeth, and its species range 
from the Middle Oolites to the Cretaceous series, in connec- 
tion with which they will be again noticed, together with the 
toothless genus Pteranodon. The genus Dimorphodon is Li- 
assic, 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 por- 
tions 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. With regard to its habits 
and mode of life, Professor Phillips remarks that, “ gifted with 
ample means of flight, able at least to perch on rocks and 
scuffle along the shore, perhaps competent to dive, though not 
so well as a Palmiped bird, many fishes must have yielded to 
the cruel beak and sharp teeth of Rhamphorhynchus. If we 
ask to which of the many families of Birds the analogy of 
