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.