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HISTORICAL GEOLOGY 



REFERENCES FOR TURTLES 



Hay, O. P., — The Fossil Turtles of North America: Carnegie Institution of Wash- 

 ington, Pub. No. 75, 1908. 

 Wieland, G. R., — Archelon, etc.: Am. Jour. Sci., Vol. 2, 1896, pp. 401-412. 

 Williston, S. W., — Water Reptiles of the Past and Present, pp. 216-241. 



Flying Reptiles (Pterosaurs). — Either because of the overcrowd- 

 ing of the land, or for some other reason, a race of flying reptiles was 



developed during the Jurassic and 

 Lower Cretaceous, and occupied the 

 realm of the air, in which there was 

 no competition. 



The pterosaurs (Figs. 518, 519, 

 520) are as extraordinary, in many 

 ways, as any animal that ever lived. 

 They had a short body, hollow 

 bones, a rather large but light head, 

 and jaws which at the beginning of 

 the race were provided with slender 

 teeth, but which in some highly 

 specialized later genera were tooth- 

 less and sheathed with horn, as in 

 modern birds. The most remark- 

 able and characteristic features, how- 

 ever, were the large, membranous 

 wings, supported by one greatly 

 elongated finger, the fourth. The 

 breastbone, to which the muscles of 

 flight were attached, was large and 

 keeled, and the shoulder girdle was 

 strong. Some had long tails with a 

 kind of rudder at the extremity, and 

 others were" tailless. The pterosaurs 

 varied greatly in size ; some were as 

 small as sparrows, some were the size of partridges, while others were 

 the largest flying creatures that ever lived, the wings measuring 

 over 20 feet from tip to tip (Fig. 520). 



One of the best known and least specialized genera of the Jurassic 

 pterosaurs (Dimorphodon ; Greek, dimorphos, two-formed, and odont-, 

 tooth) (Fig. 519) had, as the name implies, two kinds of teeth, those 

 in front of the jaw being sharp and strong and fitted for tearing, while 



Fig. 518. — A Jurassic pterosaur 

 (Rhamphorynchus). (After Von Rei- 

 chenbach.) Length about twenty 

 inches. 



