THE HABITAT OF THE SAUROPOD DINOSAURS 467. 
g) “Dinosauria.”’ The two great orders of reptiles collectively 
known as “Dinosauria”’ were represented in the Morrison by a 
variety of forms. These were all terrestrial or amphibious, perhaps 
some forms being largely fluviatile or lacustrine. Of the sauris- 
chians there were present, besides the sauropods, several types of 
carnivorous forms. Some of these were small, active, and not very 
formidable. Ornitholestes may be considered as a typical example 
of this group. Probably these small dinosaurs had little impor- 
tance, so far as the Sauropoda were concerned, unless, perhaps, 
they ate sauropod eggs. They were too small and weak to attack 
the sauropods, and by their activity and carnivorous structure 
could obtain food that would not be available for gigantic, largely 
herbivorous swamp dwellers. The larger carnivorous dinosaurs, 
such as Allosaurus, Creosaurus, and Ceratosaurus undoubtedly 
played a very important part in sauropod economy. ‘The asso- 
ciation of carnivore teeth and grooved sauropod bones is in perfect 
accordance with the idea that the sauropods were prey for the large 
carnivores. ‘The large carnivores were unquestionably land-living 
forms. It is not at all likely that they entered the water except 
under unusual circumstances or along the margins. The gigantic 
sauropods, therefore, were less likely to be attacked in the water 
than on land. This may have tended to keep the sauropods in the 
water, and may have had considerable control over the evolution 
of the group. The ornithischian dinosaurs must also have had an 
effect upon the Sauropoda, but as competitors rather than as direct 
enemies. The stegosaurs and the iguanodonts, both large and 
small, existed along with the sauropods. These forms, especially 
the stegosaurs, were probably land animals. They were herbivo- 
rous beyond all doubt. If the sauropods spent a considerable part 
of their time on land they must have come into competition with the 
predentates in the matter of getting food. Perhaps such a competi- 
tion took place early in the history of the Sauropoda, and may have 
been instrumental in forcing the latter to take to the streams, and 
finally to develop some aquatic adaptations and spend the greater 
part of their time in the water. The predentates may have aided 
the sauropods in their struggle for existence by furnishing a con- 
siderable amount of food for the carnivores. If the predentates 
