[Illustration:  FIG. 9.  REPTILES OF JURASSIC PERIOD.]

In this time of the earth’s history we have the first bird-like forms.  They were feathered creatures, with bills carrying true teeth, and with strong wings; but they were reptiles in many features, having long, pointed tails such as none of our existing birds have.  They show us that the birds are the descendants of reptiles, coming off from them as a branch does from the parent tree.  The tortoises began in this series of rocks.  At first they are marine or swimming forms, the box-turtles coming later.  Here too begin many of the higher insects.  Creatures like moths and bees appear, and the forests are enlivened with all the important kinds of insects, though the species were very different from those now living.

In the age of reptiles the plants have made a considerable advance.  Palms are plenty; forms akin to our pines and firs abound, and the old flowerless group of ferns begins to shrink in size, and no longer spreads its feathery foliage over all the land as before.  Still there were none of our common broad-leaved trees; the world had not yet known the oaks, birches, maples, or any of our hard-wood trees that lose their leaves in autumn; nor were the flowering plants, those with gay blossoms, yet on the earth.  The woods and fields were doubtless fresh and green, but they wanted the grace of blossoms, plants, and singing-birds.  None of the animals could have had the social qualities or the finer instincts that are so common among animals of the present day.  There were probably no social animals like our ants and bees, no merry singing creatures; probably no forms that went in herds.  Life was a dull round of uncared-for birth, cruel self-seeking, and of death.  The animals at best were clumsy, poorly-endowed creatures, with hardly more intelligence than our alligators.

The little thread of higher life begun in the Microlestes and Dromatherium, the little insect-eating mammals of the forest, is visible all through this time.  It held in its warm blood the powers of the time to come, but it was an insignificant thing among the mighty cold-blooded reptiles of these ancient lands.  There are several species of them, but they are all small, and have no chance to make headway against the older masters of the earth.

The Jurassic or first part of the reptilian time shades insensibly into the second part, called the Cretaceous, which immediately follows it.  During this period the lands were undergoing perpetual changes; rather deep seas came to cover much of the land surfaces, and there is some reason to believe that the climate of the earth became much colder than it had been, at least in those regions where the great reptiles had flourished.  It may be that it is due to a colder climate that we owe the rapid passing away of this gigantic reptilian life of the previous age.  The reptiles, being cold-blooded, cannot stand even a moderate winter cold, save when they are so small