2 GUIDE TO THE FOSSIL REPTILES, AMPHIBIANS, FISHES. 
limbs as effective as those of an elephant or of an ostrich. 
Some of these were massive vegetable-feeders as ponderous 
as ground-sloths; others were slim carnivores as agile as 
cats; while a few were clearly adapted for hopping or 
jumping. There were also sea-reptiles with paddles formed 
solely for swimming, and some of these animals had the 
outward shape of dolphins or porpoises, while others were of 
unique proportions, and a few might have passed for the 
traditional sea-serpent. Moreover, there were numerous 
true flying reptiles with well-developed wings supported 
by bones of a texture and construction now peculiar to 
birds. 
The Secondary period was, therefore, the “ Age of Reptiles,” 
just as the Tertiary period is the “Age of Mammals and 
Birds.” Indeed, the casual, observer on entering the Gallery 
of Fossil Reptiles may be pardoned for asking the reason 
why many of them are actually placed in the cold-blooded 
Reptilian Class and not among the warm-blooded mammals 
or birds. The brief explanation is, that they show a combi¬ 
nation of peculiarities in the skeleton which is exclusively 
characteristic of reptiles in the existing world. Although 
some of the huge Dinosaurs bear an outward resemblance to 
mammals, they cannot be associated with those quadrupeds, 
because their lower jaw consists of several pieces and is 
hinged to the skull by a large separate bone (the “ quadrate ”), 
while their ankle-joint is not at the root of the toes but 
between the two rows of ankle-bones. The Ichthyosaurs are 
not fishes, because their nose-passages and their chest-bones 
show that they breathed by lungs; while they are not 
porpoise-like mammals, because their lower jaw consists of 
several pieces and their cheek is covered with separate 
bones which encircle the peculiar “quadrate” bone. The 
Pterodactyls are not birds, because well-preserved fossils 
prove that they had no feathers, while their wings were 
arranged on a different pattern; and they are not flying, 
mammals, or bats, because they exhibit the complexity of 
the lower jaw and its connections already mentioned as 
characteristic of walking and swimming reptiles. 
In short, the modern snakes, lizards, crocodiles, turtles 
and tortoises are merely the degenerate survivors of a race 
which no longer occupies foremost rank. They give very 
little idea of the Class Reptilia as it was at its most 
flourishing period. 
