LIFE IN SECONDARY TIMES 263 



reptilian organization, resumed the life of Fishes in order to 

 hunt them and dispute with them the easy prey presented by 

 the indolent Ammonites found in every sea. 



In the course of passing through the different stages just 

 enumerated, Reptiles naturally developed new characters, 

 used by naturalists to distinguish each group leading the same 

 kind of life. At first the pelvis remained very similar to that 

 of the Crocodiles. Below the iliac bones the two pubes formed 

 a V with the apex directed forward, and the two ischia a V 

 with the apex directed backward. The Reptile could only 

 stand erect under exceptional circumstances, but it could be 

 either plantigrade or digitigrade, that is to say, it could walk 

 on the entire sole of its feet or only on the toes, the sole being 

 raised up off the ground. The Sauropoda exemplify the first, 

 and the Theropoda, with extremely elongated bodies, and the 

 Ceratopsidae with the ponderous form of our Rhinoceros, 

 exemplify the second condition. 



In another series the hind-quarters gradually assume a 

 greater development than the fore-quarters, and it is likely 

 that the animal was able to stand erect. The thigh muscles 

 consequently become larger, and the pubic bones to which 

 they were attached acquire a greater surface, and, above all, 

 present, as in birds, both an anterior and a long posterior 

 branch (post-pubis) for the insertion of the muscles that erect 

 the body ; the pelvis remains open in front as with Birds. 

 These features characterize the Orthopods. Those orthopod 

 Reptiles which continued to walk on all four feet and remained 

 plantigrade form the sub-group of Stegosaurians ; those whose 

 fore limbs are so small that the animal could no longer have 

 supported itself upon them, and must have held itself erect 

 on its hind legs in the manner of a Kangaroo, form the sub- 

 order Ornithopods. All these animals together form the sub- 

 class of Dinosaurs or giant Saurians comprising the biggest 

 and strangest terrestrial creatures that ever lived. 



Sauropods had the aspect of huge Serpents with an elephant's 

 body stuck midway of their length. At the end of a long neck 

 they carried a remarkably small head, which in Brontosaurus 

 excelsus, 1 an animal thirty metres in length, was no bigger than 

 the fourth cervical vertebra of a neck made up of thirteen. Con- 

 temporaneous with it in the Wyoming strata was Atlantosanrus 



1 Of the Upper Jurassic. 



