THE POSE AND LOCOMOTION OF DIPLODOCUS 5 



crocodiles, little and great, are curved; as were too those of their prede- 

 cessors, Aetosaurus, of the Triassic, and of Alligalorellus, of the Juras- 

 sic, the former with femora hardly four inches long, the latter with 

 these bones about an inch in length. 



Diplodocus has been erected on column-like legs partly because it 

 has been supposed that the great weight of its body required this. 

 However, the legs of animals are not straight in proportion to the 

 the weight of their bodies. The legs of the largest camels seem not to 

 be straighter than the legs of the llamas. Some rhinoceroses and 

 some oxen have very heavy bodies; nevertheless, their femora lack 

 much of being in line with their tibia and these much of being in line 

 with the metapodials. Certainly it is not because of the immense 

 weight of the body that the legs of a man are straight. 



There must, of course, be a limit to the size of an animal that can 

 move itself about on land, in whatever position; but it may be sug- 

 gested that a reptile that could not walk about as crocodiles do, rest- 

 ing at least now and then, its body on the ground, could not well 

 have erected itself when once it had lain down. That the largest 

 crocodiles are far from the limit of active movement on the land may 

 be judged from the following extract taken from W. Saville-Kent.* 



The celerity with which a huge 25-footer, as witnessed by the writer in 

 the Norman River, North Queensland, will make tracks for and hurl itself 

 into the water, if disturbed during its midday siesta by the near impact of 

 a rifle bullet, is a revelation. 



It must be further taken into consideration that the weight of a 

 crocodile 25 feet long, with short, thick neck, large head, long body, 

 and heavy tail, would be much greater than that of a sauropod of the 

 same length, in which most of the length is composed of slender neck 

 and comparatively slender tail. 



It is generally conceded that such carnivorous dinosaurs as Allo- 

 saurus, Dryptosaurus, and Tyrannosaurus, and such herbivorous 

 forms as Trachodon and Campiosaurus walked bipedally erect. If 

 now comparison be made of the femora of any of these with those of 

 the sauropods great differences will be noted. The shaft of the former 

 appears to be more elaborately modeled and to consist of finer and 

 harder bone; all the articular surfaces are smooth and they carry the 



* Living Animals of the World, p. 547. 



