THE DINOSAURS OF NORTH AMERICA. 



By O. G. Marsh. 



ENTRODUCTIOZST. 



Among the many extinct animals that lived iu this country in past 

 ages, none were more remarkable than the dinosauriau reptiles which 

 were so abundant during Mesozoic time. This group was then repre- 

 sented by many and various forms, including among them the largest 

 land animals known, and some, also, very diminutive. In shape and 

 structure, moreover, they showed great variety, and in many other 

 respects they were among the most wonderful creatures yet discovered. 



The true place of these reptiles in the animal kingdom has beeu a 

 matter of much discussion among auatomists, but the best authorities 

 now regard them as constituting a distinct subclass of the Eeptilia. 

 Some of the large, earlier forms are apparently related to the Croco- 

 dilia, while some of the later, small, specialized ones have various 

 points of resemblance to birds. These diversified characters make it 

 difficult to classify the dinosaurs among themselves, and have led some 

 writers to assert that these reptiles do not form a natural group, but 

 belong to divisions remotely connected and not derived from a common 

 ancestry. 



It is not within the province of the present article to discuss in 

 detail the classification of this group, nor to treat fully the various 

 questions relating to the genealogy of dinosaurs, about which little is 

 really known. It may, however, be stated in few words that three 

 great divisions of the Diuosauria are now generally recognized, which 

 may be properly regarded as distinct orders. For these groups the 

 writer has proposed the names Theropoda, for the one including the 

 carnivorous forms, and Sauropoda and Predentata, for the two herbiv- 

 orous groups, the last order being made up of three separate suborders ; 

 namely, the Stegosauria, the Ceratopsia, and the typical Ornithopoda. 

 The first of these suborders contains large dinosaurs more or less pro- 

 tected by a dermal covering of bony plates; the second group includes 

 the huge horned dinosaurs ; and the third is made up of the forms that 

 in shape and structure most nearly resemble birds. 



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