R. S. Lull — Dinosaurian Distrihutio 



n. 



and run with a truly bipedal gait (Say ville-Kent 1898, p. 341). 

 It is significant that the bipedal lizards, so far as my knowl- 

 edge goes, are all found in serai-arid climates — Australia, 

 Southwestern United States. This tendency toward bipedal- 

 ism, with a consequent profound alteration of the hind limbs 

 and pelvis, both in bone and musculature, seems therefore to 

 have developed to meet the need of greater range of move- 

 ment necessitated by increasing aridity, and was the prime factor 

 in the early evolution of the dinosaurian race. 



So strongly was this feature impressed, that the main lines 

 of dinosaurian evolution, whether plant or animal feeders, 

 were cursorial, terrestrial types, though, as new conditions arose, 

 or were met with during their forced migrations, aberrant 

 types of marvelous complexity and range of specialization 

 developed. These aberrant forms, from the fact that their 

 remains were more readily preserved, are the ones best known 

 to us and have colored our whole conception of the dinosaurian 

 race. 



When the plant-feeding Orthopoda arose we do not know. 

 Wanosaurus (v. Huene and Lull 1908) is known from the 

 upper Trias (or lower Jurassic) of Colorado, while in the pos- 

 sibly contemporaneons beds of the Connecticut valley there have 

 been found many footprints which Lull (1904 A, pp. 499-509) 

 has shown to belong to plant-feeding types of general propor- 

 tions not unlike those of their theropod allies, but differing 

 mainly in the feebly prehensile character of the little, blunt- 

 toed manus, the imprint of which is sometimes seen. The 

 Theropoda, on the other, hand, had a strong, grasping hallux, 

 as a rule rotated to the rear of the ,foot so as to be in opposi- 

 tion to the other toes, and a manus with powerful claws, which 

 had already sacrificed fully the function of locomotion to that 

 of prehension. The Orthopoda could give rise to secondarily 

 quadrupedal (Dollo 1905) forms, the Stegosauria, the Ceratop- 

 sia; the TherOpoda, on the other hand, had cast the die in favor 

 of absolute bipedalism and stalked on upon the hind limbs to 

 the end of their career. 



While both small and large forms prevailed at the close of the 

 Trias, the differentiation, if we except the character of the 

 pubis, is largely owing to opposite habits, acquired apparently 

 in the remote Trias, very early in the dinosaurian evolution. 



The carnivores, as has been said, are relatively conservative 

 in their evolution, except for the differentiation into the 

 greater megalosauroid forms and the lesser compsognathoid 

 types. The Theropoda were evidently the most mobile of all 

 dinosaurs, free to migrate wherever other creatures lived 

 which could possibly be utilized for prey, for not only do we 

 find them the world over, with the exception of Asia (vide 



