move faster through the soft soil, they improved upon their legs and their size

increased until the world was populated with gigantic forms (which the

hand-books of biology list under the names of Ichthyosaurus and Megalosaurus and

Brontosaurus) who grew to be thirty to forty feet long and who could have played

with elephants as a full grown cat plays with her kittens.

 

Some of the members of this reptilian family began to live in the tops of the

trees, which were then often more than a hundred feet high.

 

They no longer needed their legs for the purpose of walking, but it was

necessary for them to move quickly from branch to branch. And so they changed a

part of their skin into a sort of parachute, which stretched between the sides

of their bodies and the small toes of their fore-feet, and gradually they

covered this skinny parachute with feathers and made their tails into a steering

gear and flew from tree to tree and developed into true birds.

 

Then a strange thing happened. All the gigantic reptiles died within a short

time. We do not know the reason. Perhaps it was due to a sudden change in

climate. Perhaps they had grown so large that they could neither swim nor walk

nor crawl, and they starved to death within sight but not within reach of the

big ferns and trees. Whatever the cause, the million year old world-empire of

the big reptiles was over.

 

The world now began to be occupied by very different creatures. They were the

descendants of the reptiles but they were quite unlike these because they fed