MESOZOIC ERA: THE AGE OF REPTILES 



539 



which brought the Paleo- 

 zoic to a close and spread 

 over three continents, but 

 became extinct before the 

 beginning of the Jurassic. 

 It has been suggested that 

 their rapid development 

 and great variation may 

 have been due to a more 

 oxygenated atmosphere re- 

 sulting from the with- 

 drawal of the carbon di- 

 oxide which was abstracted from the atmosphere to form coal in the 

 Carboniferous. It is possible that their extinction was due to com- 

 petition with the better organized reptiles of the Triassic. 



Fig. 502. — Skull of a large, carnivorous, mammal- 

 like reptile (theromorph), Inostranservia. The skull 

 is nearly two feet long. 



REFERENCES FOR REPTILES WITH MAMMALIAN CHARACTERS 



Broom, R., — South African Fossil Reptiles: Am. Museum. Jour., Vol. 13, 1913, pp. 



335-346, and Vol. 14, 1914, pp. 139-143. 

 Hutchinson, H. N., — Extinct Monsters and Creatures of Other Days, pp. 105-117. 

 Lankester, E. R., — Extinct Animals, pp. 209-222. 



Dinosaurs 



The preeminent land animals of the Mesozoic were the dinosaurs 

 (Greek, deinos, terrible, and saurus, reptile), which occupied the 

 place in nature now held by the land mammals. Some were larger 

 than the largest animals of the present day, with the exception of a 

 few of the whales, while others were as small as a common fowl ; some 

 walked in a more or less erect position, while others moved about on all 

 fours; some had limbs as light as birds, while the limb bones of others 

 were the largest and heaviest known ; some were covered with a bony 

 armor, and others were without such protection ; some were very 

 agile, others were slow-moving ; some were carnivorous, others her- 

 bivorous ; all were alike in having very small brains. All the conti- 

 nents of the world, including Australia, were occupied by them. 



The dinosaurs may be separated into four groups: (1) carnivores 

 (Theropoda), (2) unarmored quadrupeds (Sauropoda), (3) unar- 

 mored bipeds (unarmored Predentata), and (4) armored dinosaurs 

 (armored Predentata). Of these, the first only was carnivorous, 

 the others being herbivorous. 



