THE TRIASSIC PERIOD. 43 



the period. Some of the orders came into the record so near the 

 close of the period that they play little part in its f aunal history. Such 

 are the true crocodilians, the flying saurians (Pterosauria) and the scaled 

 reptiles (Squamata) , which include the lizards, clolichosaurs, pythono- 

 morphs and snakes. A true lizard has recently been reported by 

 Broom from South Africa. 



The rise of the dinosaurs. — A foremost feature was the advent 

 and rapid evolution of the reigning reptilian dynasty of the Mesozoic. 

 Arising probably from some of the more primitive forms of the 

 rhynchocephalians, the dinosaurs (terrible saurians) were at first 

 generalized and rhynchocephalian in aspect, but later became more 

 specialized and diverged widely. While some were small and delicate 

 in structure, the more noted forms were gigantic and ungainly to 

 an extreme degree, especially the herbivores of the following periods, 

 when the deployment of the order was at its climax. Only the car- 

 nivorous forms (Theropoda) are known in the Trias, and these were 

 not usually as yet gigantic. Their general form is indicated by the 

 partially restored skeleton shown in Fig 340. The strong develop- 

 ment of the hinder parts, the relative weakness of the fore limbs, and 

 the kangaroo-like attitude, are the most obvious features. The bones 

 of these upright-walking forms were hollow, and certain other struc- 

 tural features resembled those of birds, among them the reduction 

 of the functional toes of the hind feet to four, with one of these much 

 shorter than the others so that their tracks were often three- toed, like 

 the famous "bird tracks" of the Connecticut valley. As the bones 

 of the Anchisaums and allied genera are the only relics found with 

 these "bird tracks," it is supposed that they and their relatives were 

 responsible for them, which is made the more probable by the occa- 

 sional imprint of the fourth toe and of the fore foot. Most of the 

 bird-like characters of the dinosaurs are more probably due to parallel 

 evolution than to any immediate ancestral relationship to birds; more 

 remotely, birds and dinosaurs probably arose from a common stock. 

 The dinosaurs will claim much further attention in the following 

 periods. Even as early as the Triassic, they had a wide and signifi- 

 cant distribution, appearing in the Rocky Mountains, North Carolina, 

 Pennsylvania, Connecticut, Prince Edwards Island, England, Scotland, 

 France, Germany, India, and South Africa. 



The advanced differentiation of the chelonians, — The turtle tribe 



