MESOZOIC ERA: THE AGE OF REPTILES 549 



tection. The toes, five in front and three behind, were provided 

 with hoofs. 



Triceratops, unlike Stegosaurus, faced its enemies, as do cattle 

 to-day. Punctures of the skull and frill over the neck, and broken 

 horn cores are frequently found, showing that Triceratops often had 

 combats with other animals. These creatures had the largest heads 

 and smallest brains for their bulk of any of the reptiles, and were 

 unquestionably extremely stupid, depending upon their size and 

 armor for protection. During the life of the race, the animals in- 

 creased in size and developed longer horns and a more complete frill 

 over the neck. Triceratops had a relatively brief career, beginning 

 in the Cretaceous and disappearing with its close. 



Summary of Dinosaurs. — Dinosaurs are first known from the 

 Triassic, at which time they were numerous and divefsified, as is 

 shown by the great number and variety of footprints in the Triassic 

 sandstone, although few skeletons have been found. This class 

 became more abundant, larger, and more varied in the Jurassic, 

 culminating either in that period or in the Cretaceous. During the 

 Mesozoic, they became more and more specialized, the specialization 

 culminating in Stegosaurus and Triceratops among the herbivores and 

 in Tyrannosaurus among the carnivores. After becoming adapted 

 to widely different conditions of life, assuming many strange forms 

 and spreading over all the continents of the world, they disappeared 

 with the Mesozoic and left no descendants. 



Migration and Extinction of Dinosaurs. — Our knowledge of the 

 reptilian life of the Mesozoic lands is almost entirely confined to that 

 which lived in the delta and coastal swamps of the era : the bronto- 

 saurs, the trachodons, the tyrannosaurs are all dinosaurs that lived 

 either in swamps or on their margins. Of the upland reptiles little is 

 known. At the close of the Jurassic the gigantic dinosaurs were al- 

 most completely wiped out, doubtless because of the draining of the 

 swamps in which they lived and their inability to adapt themselves 

 to other conditions. Early in the Cretaceous, however, the swamps 

 were again populated by other huge dinosaurs as well as many of 

 smaller size. This fauna was a new one and was not descended from 

 that of the previous period. Either it (1) migrated from some region 

 as yet unknown or, more probably, (2) was developed from surviving 

 small, active denizens of the uplands which are as yet practically 

 unknown. Towards the close of the Mesozoic (in the late Cretaceous) 

 the modern type of vegetation was probably associated with the 



