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Comparative Morphology of Chordates 



Fig. 394. Diagrams showing types of temporal openings in reptiles. (A) Anapsid. 

 (B) Synapsid. (C) Parapsid. (D) Diapsid. (j) Jugal; (p) parietal; (po) postorbital; 

 (sq) squamosal. (Courtesy, Romer: "The Vertebrate Body," Philadelphia, \\ . B. 

 Saunders Co.) 



During the Cretaceous Period the reptiles went into a decline so 

 rapid — that is, in terms of geologic time — as to be fairly called cata- 

 clysmic. By the end of the period, the reptilian masters of the Mesozoic 

 world had become entirely extinct. Nothing survived of the Class but 

 the five Orders which have come down to the present. The causes of 

 reptilian decline are obscure. Probably changes in configuration of 

 lands and waters were accompanied by climatic changes which upset 

 the biologic balance of vegetation and animal life. Reptiles of today 

 are not only a small remnant of a once mighty group, but a dwindling 

 remnant, for many of them seem fated for early extinction. Their 

 greatest enemy is the human mammal with his liking for terrapin, 

 turtle soup, and alligator leather, and his unreasonable antipathy 

 toward harmless snakes and lizards. 



