80 Evolution 



parrot-like beak; the Plesiosaurus, with its long lizard- 

 like body, the Deinosaurus, and many another formidable 

 reptile. The climate is still warm, food abounds, and 

 the reptile lords it over creation and grows to a 

 prodigious size. As time goes on we get the voracious 

 Ichthyosaurus, more than twenty feet long, with (some- 

 times) two hundred teeth, and eyes fifteen inches across: 

 the Iguanodon, thirty feet long; the Megalosaurus, 

 thirty feet long; the Ceteosaurus, fifty feet long; the 

 Atlantosaurus, one hundred feet long ; and the Bronto- 

 saurus, sixty-seven feet long and weighing probably 

 ninety tons, which has left "on the sands of time" — or 

 the Jurassic mud-flats — footprints that cover about a 

 square yard. And overhead are grotesque flying lizards 

 that have taken refuge in the air in the increasingly 

 bloody struggle for life. 



How all these giants came to perish, and the reptile 

 world fell from its high estate to become a collection of 

 skulking serpents and lizards and crocodiles would take 

 us too far afield to consider. One word will suffice. 

 Imagine the climate of the earth sinking considerably, 

 so that the cold-blooded egg-laying reptile must move to 

 the restricted regions where it is still warm enough for 

 his life. Food will grow scarce, the little reptiles that 

 need least food will survive, and the colossal creatures 

 die out. If on top of this we assume the advent of a 

 race of higher intelligence and greater speed, the ex- 

 planation will be complete enough. And this is pre- 

 cisely what happened in the Cretaceous period. 



The emergence of the continents in the Devonian, 

 and the lowering of the temperature in the Cretaceous, 

 stand out as critical points in the story of the earth. 

 Towards the end of the Jurassic began that lowering of 

 the temperature which culminated in the local glaciers 

 and the deciduous trees of the Cretaceous. The change 



