10 B. 8. Lull — Dinosaur ian Distribution. 



Orthopoda. 



The Orthopod dinosaurs were adapted to a very different 

 kind of food from that of the Sauropoda, developing in the 

 course of their evolution a more and more perfect dental 

 mechanism for chopping into short lengths the relatively firm 

 terrestrial vegetation. The toothless anterior part of the 

 mouth was sheathed in a leathery or horny beak which reached 

 its highest perfection in the Ceratopsia and which constituted 

 the prehensile, while the teeth, borne in the posterior portion 

 of the jaws, formed the masticatory part of the mouth; best 

 developed in the Ceratopsia (Hatcher 1907, pp. 43-46) on the 

 one hand and the Trachodontidae (Brown 1908, pp. 52-53) on 

 the other. 



The Sauropoda and Theropoda- had only prehensile teeth 

 and did not masticate their food at all. This shows quite 

 clearly that, so far as feeding habits go, none of the three 

 great groups of dinosaurs came into competition with each 

 other, except that the carnivores did occasionally devour the 

 others, and that, in so far as the Sauropoda and Orthopoda 

 were concerned, the habitat was necessarily different; the 

 latter being in the main terrestrial, the former amphibious. 

 In no other way can we account for the marked differences in 

 distribution of the two orders which, reduced to its final analy- 

 sis, has gone so far that the two groups are rarely found in the 

 same quarry even within the same region and geological forma- 

 tion. For example, " Quarry 13 " (Gilmore, 1909, p. 299) 

 in Como Bluff, Wyoming, from which several of Professor 

 Marsh's more important type specimens came, contains almost 

 entirely the remains of Orthopoda, Camptosaurus, Dryosati- 

 rus, Stegosaurus ; of Carnivores, Allosaurus and Cmlurus, 

 while but a single Sauropod, the type of Morosaurus lentus, an 

 extremely young individual, was found in association. On the 

 other hand, the famous Bone Cabin Quarry, situated but a few 

 miles distant, had yielded up to 1904 (Osborn, 1904, p. 694) 

 sauropods, 44 ; stegosaurs, 3 ; smaller herbivorous dinosaurs, 4 ; 

 large carnivorous dinosaurs, 6 ; small carnivorous dinosaurs, 3 ; 

 showing the Sauropoda to be vastly more numerous than the 

 other plant-feeding varieties, and evidently implying a distinct 

 habitat from that represented by " Quarry 13." 



Within the Orthopoda the marked differentiation into 

 Ornithopoda, or unarmored types, and the Stegosauria and 

 Ceratopsia, or armored forms, seems to have been due to their 

 different modes of defence, presumably against the omnipresent 

 carnivores, though the existence of enemies other than dinosaurs, 

 such as the crocodile Goniopholis, is not unlikely. The 

 Ornithopoda, which were the most conservative in their evolu- 



