720 GEOLOGY 



destruction. In the same beds are the remains of many land in- 

 sects, not a few of them being wood-eating beetles. 



In the closing stages of the period, the area of land was extent le< 1 . 

 This should in itself have been favorable to an expansional develop- 

 ment of plants; but extensions of land are so liable to be attended 

 by adverse climatic and topographic changes, that no safe inference 

 can be drawn except from the actual record, which, in this case, is 

 rather scanty. 



Animals. Of the North American land faunas of the Jurassic, 

 except perhaps its latest stages, little is known. But with the close 

 of the period there appeared in the Morrison beds (p. 705) a rich 

 but not varied land fauna, composed chiefly of dinosaurs. These 

 animals attained remarkable size and diversity, and were easily 

 lords of the reptile horde. Some were large, and some were small, 

 and the group, as a whole, developed great diversity in many 

 directions. There were not only carnivorous types, which had ap- 

 peared in the Triassic, but numerous herbivorous forms. Among 

 them all there was not a single type which was distinctively North 

 American. It is therefore concluded that there was freedom of 

 migration between the eastern and western continents at this time. 



Of the carnivores, one of the most typical was Ceratosaurus 

 nasicornis (Fig. 492) . The fore limbs seem to have been used chiefly 

 for seizing and holding prey, rarely for walking. The animal's pose 

 was facilitated by hollow bones. The head was relatively large, 

 an unusual character for a race among which small heads and 

 brains were the fashion of the time. Not all the carnivorous dino- 

 saurs were large. There were small leaping forms (like Comjw)- 

 gnothus) not larger than a rabbit. 



The herbivorous dinosaurs are known first in this system, but 

 their development was so extraordinary that they soon outranked 

 the carnivorous forms in both size and diversity. The sai<r<>/><><l<i 

 were generally massive, with sub-equal limbs and the quadruped 

 habit. Among them, Brontosaurus (Apatosaurus) attained the 

 extraordinary length of 60 feet and possibly more, taking rank as 

 one of the largest of known land animals (Fig. 493) . This enormous 

 creature was characterized by weakness rather than strength, 

 for its general organization was unwieldy, its head <niall, and its 



