1 8 OLIVER P. HAY 



birds, but the remains of such are found in the Triassic no more than 

 those of birds. 



If now such Theropoda as Anchisaurus colurus, more advanced 

 probably in every respect than the Sauropoda ever were, did not walk 

 habitually erect, like mammals, on either two or four legs, but pro- 

 gressed either in more or less crocodilian manner on all fours or in a 

 straddling way on the hind legs, is, it probable that the sauropods ever 

 walked high up on four legs in the jaunty manner in which they have 

 been represented ? It is to be considered that these great herbivorous 

 reptiles possessed a huge abdomen, deep and probably broad, which 

 extended backward and merged into the tail, necessitating the diver- 

 gence of the relatively long femora. The outer surfaces of the pubic 

 and ischiadic bones were clothed with great masses of muscles, as 

 were too the insides of the femora. Assuming that the legs were as 

 straight as they have been represented, the feet could have been hardly 

 closer together than the knees, probably considerably farther apart. 

 A bulky animal walking thus could preserve its equilibrium only by 

 either swaying the body from side to side, to throw it over the ad- 

 vanced foot, or throwing the tail toward that side. In the case of the 

 fore foot the long neck might be used to preserve the balance. One 

 might amuse and instruct himself by working out the movements of 

 the animal according as it was walking, trotting, pacing, or per- 

 chance galloping. 



The writer is not willing to assert that Diplodocus and its relatives 

 never straightened out their legs, thus lifting themselves well above 

 the ground, and never walked thus. Even the crocodiles have been 

 known to do this, as a rare occurrence. 10 In the U. S. National 

 Museum there is a specimen of the Florida crocodile mounted in this 

 position. The femora are directed forward and outward, the tibiae 

 downward. The feet are widely separated as a mechanical neces- 

 sity. What is disputed by the present writer, is that this was the cus- 

 tomary attitude of the sauropods; and their great bulk makes it 

 doubtful if it was ever assumed. 



The writer is of the opinion that the feet of the primitive dinosaurs 

 had the inner digits somewhat more strongly developed than the 

 median and outer ones; that is, they were entaxonic, not mesaxonic, 



10 Hornaday, Two Years in the Jungle, pp. 55, 266. 



