4 R. S. Lull — Dinosaurian Distribution. 



These relationships are expressed in the table (figure 1), 

 which is largely compiled from lesser ones by v. Huene (1907- 

 1908, pp. 340/375, 377; 1909, p. 22). 



III. Habitats and Adaptations. 



In order to comprehend the remarkable geographical distri- 

 bution of the dinosaurs, it is necessary to investigate the 

 character of their various habitats, the conditions they were 

 forced to meet and the marvelous degree of adaptation to the 

 environment which they underwent. 



I imagine the conditions which gave to the dinosaurs their 

 initial evolutionary trend were such as are thought to have 

 prevailed, beginning in the Permian, throughout Triassic 

 time. This is well shown in the region now known as the 

 Connecticut valley. The older notion of the estnarine origin 

 of these deposits has been abandoned in favor of the idea that 

 they were of terrestrial origin, the climatic conditions being 

 those of semi-aridity with areas here and there which were 

 subject to inundations occurring in times of torrential rains 

 such as are observed to-day under similar climatic conditions 

 in different portions of our globe. This lends color to the 

 view that the early dinosaurs were truly terrestrial types, with 

 marked cursorial adaptation, indicated in the free, bipedal 

 stride and compact, bird-like foot which is shown by the fossil 

 footprints. 



Y. Huene (1907-1909, pp. 396-401) derives the Theropoda 

 and Parasuchia from one stem, the supposition being that the 

 distinguishing characteristics were developed during the oldest 

 Trias through adaptation. Increasing aridity of climate would 

 render it necessary for an animal to go farther afield for water and 

 possibly for food and thereby place a premium on good powers 

 of locomotion, so that selection would be very active in weed- 

 ing out the unfit or inadaptable lines. This locomotor adapta- 

 tion in the quadrupedal stage is beautifully shown in the 

 Parasuchian genus Stegomus (Lull 1904 B, pp. 147-148) from 

 the Connecticut valley Trias (Rhsetic), evidently a persistent 

 type which, possibly because of the retention of armor, 

 remained a quadruped though long of limb and with the 

 greater portion of the weight borne on the hinder extremities. 

 Stegomus, I imagine, though belonging, morphologically, to a 

 very different race, represents a stage in the adaptation of the 

 dinosaurs which was reached early in the Trias. 



Many modern lizards are amazingly swift of movement, but 

 their journeys are brief and the rapidly moving types are 

 small. It is a well known fact that a number of lizards, nota- 

 ably Chlamydosaurus, when startled, rise on the hinder limbs 



