208 DINOSAURS OF NORTH AMERICA. 



TRICERATOPS. 



THE SKULL. 



The skull of Triceratops, the best-known genus of the family, has many 

 remarkable features. First of all, its size, in the largest individuals, 

 exceeds that of any land animal hitherto discovered, living or extinct, 

 and is surpassed only by that of some of the cetaceans. The skull rep- 

 resented (one-ninth natural size) on PI. LIX is one of the most perfect 

 yet discovered. Those shown on PI. LX, figs. 1-3, are both of compara- 

 tively young animals, but are about 6 feet in length. The type speci- 

 men of Triceratops horridus was an old individual, and the head, when 

 complete, must have been 7 or 8 feet long. Two other skulls, nearly 

 perfect, from the same horizon, have equal or still greater dimensions. 



Another striking feature of the skull is its armature. This consisted 

 of a sharp, cutting beak in front, a strong horn on the nose, a pair of 

 very large pointed horns on the top of the head, and a row of sharp 

 projections around the margin of the posterior crest. All these had a 

 horny covering of great strength and power. For offense and defense 

 they formed together an armor for the head as complete as any known. 

 This armature dominated the skull, and in a great measure determined 

 its form and structure. In some forms the armature extended over 

 portions of the body. 



The skull itself is wedge-shaped in form, especially when seen from 

 above. The facial portion is very narrow, and much prolonged in front. 

 In the frontal region the skull is massive and greatly strengthened, to 

 support the large and lofty horn cores which formed the central feature 

 of the armature. The huge, expanded, posterior crest, which over- 

 shadowed the back of the skull and neck, was evidently of secondary 

 growth, a practical necessity for the attachment of the powerful liga- 

 ments and muscles that supported the head (PI. LX, figs. 2 and 4). 



THE ItOSTHAL BONE. 



The front part of the skull shows a very high degree of specialization, 

 and the lower jaws have been modified in connection with it. In front 

 of the premaxillaries there is a large, massive bone not before seen in 

 any vertebrate, which the writer has named the rostral bone (os ros- 

 trate). It covers the anterior margin of the premaxillaries, and its 

 sharp inferior edge is continuous with their lower border. This bone 

 is much compressed, and its surface is very rugose, showing that it was 

 covered with a strong, horny beak. It is a cartilage ossification, and 

 corresponds to the predentary bone below. 



. The latter in Triceratops is also sharp and rugose, and likewise was 

 protected by a strong, horny covering. The two together closely resem- 

 ble the beak of some turtles, and as a whole must have formed a most 

 powerful weapon of offense. 



In one skull figured (PI. LX, fig. 1) the rostral bone was free, and was 

 not obtained. This was also true of the predentary bone and the nasal 



