CHAPTER III. 



OSTEOLOGY OF THE CERATOPSID^. 



The following rather detailed description of the osteology of the Ceratopsidse is for the 

 most part based on the genus Triceratops. I have selected this genus, both because its osteology 

 is more completely represented in the collections at my disposal than that of any of the other 

 genera of the group, and because it is,, on the whole, less divergent and more fairly representa- 

 tive of the family than most of the other genera. While this description of the osteology will 

 in the main be based on remains pertaining to the genus Triceratops, reference will occasionally 

 be made to material pertaining to other genera, more especially where striking and important 

 structural or morphological differences are displayed. 



THE SKUXIi. 



All the more important elements of the reptilian skull are present in the Ceratopsia, though 

 in many instances they are so much modified as to bear little resemblance to their homologues 

 in the skull of most other members of the Reptilia. 



In the Ceratopsia perhaps more than in any other group of reptiles, fossil or recent, the 

 skull has become greatly modified and specialized in certain directions. The chief specializa- 

 tion has been in the direction of affording increased protection and in the development of more 

 efficient organs for procuring food. Specialization along the former line has residted in the 

 development of the powerful armature seen in the nasal and frontal horns, the enormous expan- 

 sion of the parietals and squamosals, and the development of the epijugals and epoccipitals. 

 The development of the predentary and rostral bones doubtless increased the animal's ability 

 to obtain food, while they at the same time served as additional protective organs. The com- 

 pact nature of the skull as a whole is a striking feature in this group of dinosaurs and contrasts 

 strongly with the loose and open structure so characteristic of the theropod and sauropod 

 dinosaurs and of the skulls of most other reptiles, living and extinct, where the different cranial 

 elements are, for the most part, reduced to more or less slender rods, usually separated by large 

 vacuities and loosely attached to one another, the union between the different elements often 

 being only cartilaginous. The inclosed and compact nature of the skull in the Ceratopsidse 

 was of the greatest value as a means of protection. It parallels that seen in most mammals 

 and is shown, though in a less perfect condition, in most of the Chelonia, as also in Pareiasaurus 

 and the anomodont reptiles. 



The more striking features just noticed as being present in the skull are well shown in 

 fig. 5, taken from a photograph of the type of Triceratops prorsus mounted in the Yale Museum. 

 The broad, hood-like parietal crest; the powerful supraorbital horn cores laterally placed and 

 projecting forward and upward; the somewhat less powerful median nasal horn, projecting 

 almost directly forward; the formidable cutting beak formed by the opposing rostral and 

 predentary bones, borne respectively by the premaxillaries and dentaries; the large laterally 

 placed orbits and narial orifices and the comparatively small laterotemporal fontanelles are 

 conspicuous and striking features, at once distinguishing the skull of the Ceratopsidse from 

 that of any other known family of reptiles. Seen from above, the skull appears wedge-shaped 

 with the apex directed anteriorly. 

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