xtinct 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 kind