No. .)2o] 



THE SACROPODOUS DINOSAURS 



555 



lighter and smaller dinosaurs of the upland visited to a 

 greater or less degree. 



Dr. Hay makes considerable use in his discussion of 

 Marsh's restoration of Aiicliisaurus, as in this reconstruc- 

 tion the limbs appear relatively shorter and the pro- 

 portions more lizard-like than in most Theropoda. But 

 while this is true to some extent of Anchisaurus and ap- 

 parently of most Triassic Theropoda, it is exaggerated 

 in Marsh's reconstruction by insertion of several addi- 

 tional dorsal vertebra? which are probably not warranted. 3 

 The restoration is a composite from two or three partial 

 skeletons ; the number of vertebrae is really uncertain. If 

 the body be shortened to the proportions of the more 

 completely known dinosaurs, there is less difficulty in 

 -apposing the animal to have been habitually bipedal, and 

 bird-like in gait. The general contention that the dino- 

 saurs evolved from a crawling lizard-like gait to a bipedal 

 bird-like gait without passing through a quadrupedal 

 walking mammal-like gait appears probable enough. But 

 the Sauropoda seem to be most easily explained by the 

 hypothesis that they acquired secondarily a quadrupedal 

 elephantine gait, that they were at first more or less 

 amphibious and finally exclusively aquatic waders. 



Whether we state, as does von Huene, that the Sauro- 

 poda are derived from Theropoda, or, as Dr. Hay will 

 have it, that the Theropoda are derived from Sauropoda 

 seems to be largely a question of terms and definitions. 

 Both are derivable from a common ancestral group, but 

 the Sauropoda have specialized fully as much in one 

 direction as the Theropoda in another. In fact, in the 

 present writer's opinion, the Sauropoda are decidedly 

 more specialized, although their specialization is in part 

 degenerative and a re-adaptation to the aquatic environ- 

 ment of the remote ancestors of the Reptilia. 



