CHAPTER II. 



CLASSIFICATION AND REPRESENTATION OF THE CERATOPSIA. 



CLASSIFICATION OF THE CERATOPSIA. 



Class: Reptilia. 



Subclass: Dinosauria Owen. 



Order : Predentata Marsh 



Suborder: Ceratopsia Marsh. 



Family: Ceratopsidse Marsh (Agathaumidse Cope). 



In the above scheme of classification I have regarded the Dinosauria as deserving the rank 

 of a subclass, as was proposed by Marsh. While the Dinosauria embraces forms which it 

 appears to the present writer are sufficiently diverse in character to entitle the group to be 

 ranked as a subclass," still, on the other hand, there are a number of important characters 

 common to all dinosaurs which would appear to justify the recognition of the Dinosauria as a 

 natural group, although this has been denied by some authorities, and especially by the late 

 Dr. George Baur, who held that the Dinosauria was not a natural group, but that it was com- 

 posed of three distinct groups having no characters in common and showing no close relation- 

 ships. These three groups were, according to Baur, the Iguanodontia ( = Predentata Marsh), 

 Cetiosauria ( = Sauropoda Marsh), and Megalosauria ( = Theropoda Marsh). 



In the light of our present knowledge concerning the structure of these extinct animals 

 the position taken by Baur does not seem tenable. Without entering upon an extended discus- 

 sion of the classification of dinosaurs, which would be quite out of place in this connection, it 

 may be well to state briefly just what are the views held by the author of this monograph and 

 to set forth some of the more important reasons therefor. 



The following characters, first pointed out by the late Professor Marsh as possessed in 

 common by all dinosaurs, would seem to be of sufficient importance to warrant their being 

 considered as a natural group distinct from all other reptiles. These are: 



1. Teeth with distinct roots, either fixed in more or less distinct sockets or in longitudinal grooves, never ankylosed; no 

 palatal teeth. 



2. Skull with superior and inferior temporal arches. 



3. Double-headed cervical and thoracic ribs. 



4. Sacral vertebrae coossified and more numerous than in other reptilia; seldom less than five. 



5. Ilium extended in front of acetabulum, in the construction of which latter the ilium, ischium, and pubis take part. 



6. Fibula complete. 



7. The reduction in number of digits commences with the fifth. 



On the other hand, since we find within this group great diversity in form, structure, and 

 habit, some of its members being carnivorous while others are herbivorous, some quadrupedal 

 and others functionally bipedal, some unarmored while others are heavily armored, with all 

 the many and diverse anatomical characters shown in their osteology which might reasonably 

 be expected from such diversity of habits, there would seem no good reason why they should 

 not form a subclass of the Reptilia comparable, for example, with the Metatheria among the 

 Mammalia, and divisible into three orders, for each of which several names have been proposed 

 by various authors. Of all these those proposed by Marsh appear the most appropriate. These 

 are: . 



1. The Theropoda, embracing all the carnivorous dinosaurs. 



2 The Sauropoda, embracing all the herbivorous forms in which the predentary is wanting. 



3. The Predentata, embracing all the herbivorous forms in which the predentary is present. 



a Osborn considers the group a superorder within the subclass Diapsida Osborn. — R. S. L. 

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