518 THE JURASSIC PERIOD 



measured about 30 feet in length, and 18 in height in the walking 

 posture. 



The stegosaurs were quadrupedal in habit, and had solid bones. 

 Though not so large as some of the preceding, they were curiously 

 armored, and formed a very remarkable group that frequented 

 England and Western America. The Stegosaurus of Colorado and 

 Wyoming (Morrison beds) was one of the most unique (Fig. 441). 

 Its diminutive head and brain imply a sluggish, stupid creature, de- 

 pending for protection on its bulk and armor. 



A unique feature of the period was the development of pterosaurs, 

 or flying reptiles. Appearing at the close of the Trias in a few yet 

 imperfectly known forms, they were at the opening of this period, 



Fig. 442. Rhamphorhynchus phyllurus, a flying saurian. (Restored by Marsh.) 



fully developed flying animals, and later formed a diversified group 

 which included long-tailed (Fig. 442) and short-tailed forms (Fig. 

 443). With little doubt they sprang from some agile, hollow- 

 boned saurian, more or less akin to the slender, leaping dinosaurs. 

 Between the ponderous forms (Figs. 440, 441) and the pterosaurs 

 (Fig. 442), the Jurassic saurians present strange contrasts. 



Jurassic pterosaurs were small, but their successors attained 

 a wing-spread of nearly a score of feet. They were curiously com- 

 posite in structure and adaptation. Their bones were hollow, their 

 fore limbs modified for flight, their heads bird-like, and their jaws 

 set with teeth, though toothless forms appeared later. They were 

 provided with membranes stretched, bat-like, from the fore limbs 

 to the body and hind limbs, which served as organs of flight (Fig. 

 442). The fifth, or as some paleontologists believe, the fourth front 

 digit was greatly extended, and supported the wing-membrane. 

 The sternum was greatly developed, implying true powers of flight, 



