214 



THE ORIGIN AND EVOLUTION OF LIFE 



Recently restored skeleton of the light-limbed, 

 bird-like, toothless "ostrich'' dinosaur, Slriith- 

 iomimus {Ornithomimus), after Osborn. 



its toothless jaw sheathed in horn. In this animal the car- 

 nivorous habit is completely lost; it is secondarily herbivorous. 



Its limbs are adapted to 

 very rapid motion. 



In the meantime the 

 true carnivorous dinosaur 

 line was evolving over 

 the entire northern hemis- 

 phere stage by stage with 

 the evolution of the varied 

 herbivorous group of the 

 dinosaurs. These animals 

 preserved perfect me- 

 chanical unity in the evo- 

 lution of the very swift 

 motions of the hind limb 

 and prehensile powers 

 both of the jaws and of 

 the hind feet, adapted to 

 seizing and rapidly over- 

 coming a struggling 

 powerful prey. This series 

 reaches an astounding 

 climax in the gigantic 

 Tyrannosaurus rex, de- 

 scribed by Osborn from 

 the Upper Cretaceous of 

 Montana (see frontis- 

 piece). This "king of the tyrant saurians" is in respect to 

 speed, size, power, and ferocity the most destructive life 

 engine which has ever evolved. The excessively small size of 

 the brain, probably weighing less than a pound, which is less 



Lateral view of the "tyrant" dinosaur, Tyran- 

 nosaurus (left), and the "ostrich" dinosaur, 

 Slruthiomimus (right), to the same scale. 



Fig. 92. Extremes of Adaptation in the 

 "Tyrant" and the "Ostrich" Dinosaurs. 



Skeletons mounted in the American Museum of 

 Natural History. 



