Dinosaurs | Page 2

deer and of other quadrupeds
large and small which are now extinct; but most of its animals were the
same species as now exist. It was marked by the great episode of the
Ice Age, when considerable parts of the earth's surface were buried
under immense accumulations of ice, remnants of which are still with
us in the icy covering of Greenland and Antarctica.
The Age of Mammals. Before this period was a very much longer

one--at least thirty times as long--during which modern quadrupeds
were slowly evolving from small and primitive ancestors into their
present variety of form and size. This is the Tertiary Period or Age of
Mammals. Through this long period we can trace step by step the
successive stages through which the ancestors of horses, camels,
elephants, rhinoceroses, etc., were gradually converted into their
present form in adaptation to their various habits and environment. And
with them were slowly evolved various kinds of quadrupeds whose
descendants do not now exist, the Titanotheres, Elotheres, Oreodonts,
etc., extinct races which have not survived to our time. Man, as such,
had not yet come into existence, nor are we able to trace any direct and
complete line of ancestry among the fossil species known to us; but his
collateral ancestors were represented by the fossil species of monkeys
and lemurs of the Tertiary period.
[Illustration: Fig. 1.--The Later Ages of Geologic Time.]
The Age of Reptiles. Preceding the Age of Mammals lies a long vista of
geologic periods of which the later ones are marked by the dominance
of Reptiles, and are grouped together as the Age of Reptiles or
Mesozoic Era. This was the reign of the Dinosaurs, and in it we are
introduced to a world of life so different from that of today that we
might well imagine ourselves upon another planet.
None of the ordinary quadrupeds with which we are familiar then
existed, nor any related to nor resembling them. But in their place were
reptiles large and small, carnivorous and herbivorous, walking,
swimming and even flying.
Crocodiles, Turtles and Sea Reptiles. The Crocodiles and Turtles of the
swamps were not so very different from their modern descendants;
there were also sea-crocodiles, sea-turtles, huge marine lizards
(Mosasaurs) with flippers instead of feet; and another group of great
marine reptiles (Plesiosaurs) somewhat like sea-turtles but with long
neck and toothed jaws and without any carapace. These various kinds
of sea-reptiles took the place of the great sea mammals of modern times
(which were evolved during the Age of Mammals); of whales and
dolphins, seals and walruses, and manatees.

Pterodactyls. The flying Reptiles or Pterosaurians, partly took the place
of birds, and most of them were of small size. Strange bat-winged
creatures, the wing membrane stretched on the enormously elongated
fourth finger, they are of all extinct reptiles the least understood, the
most difficult to reconstruct and visualize as they were in life.
Dinosaurs. The land reptiles were chiefly Dinosaurs, a group which
flourished throughout the Age of Reptiles and became extinct at its
close. "Dinosaur" is a general term which covers as wide a variety in
size and appearance as "Quadruped" among modern animals. And the
Dinosaurs in the Age of Reptiles occupied about the same place in
nature as the larger quadrupeds do today. They have been called the
Giant Reptiles, for those we know most about were gigantic in size, but
there were also numerous smaller kinds, the smallest no larger than a
cat. All of them had short, compact bodies, long tails, and long legs for
a reptile, and instead of crawling, they walked or ran, sometimes upon
all fours, more generally upon the hind limbs, like ostriches, the long
tail balancing the weight of the body. Some modern lizards run this
way on occasion, especially if they are in a hurry. But the bodies of
lizards are too long and their limbs too small and slender for this to be
the usual mode of progress, as it seems to have been among the
Dinosaurs.
ANIMALS OF THE AGE OF REPTILES. LAND REPTILES.
DINOSAURS corresponding to the larger quadrupeds or land
mammals of today. CROCODILES, LIZARDS AND TURTLES still
surviving. SEA REPTILES. PLESIOSAURS } corresponding to
whales, dolphins, seals, ICHTHYOSAURS } etc., or sea-mammals of
today. MOSASAURS } FLYING REPTILES OR PTEROSAURS.
BIRDS WITH TEETH (scarce and little known). PRIMITIVE
MAMMALS of minute size (scarce and little known). FISHES and
INVERTEBRATES many of them of extinct races, all more or less
different from modern kinds.
Fishes, large and small, were common in the seas and rivers of the Age
of Reptiles but all of them were more or less different from modern
kinds, and many belonged to ancient races now rare or extinct.

The lower animals or Invertebrates were also different from those of
today, although