A HISTORY OF VERTEBRATES: AMPHIBIANS AND REPTILES 467 



Their mammalian descendants remained a rather inconspicuous part 

 of the fauna until the disappearance of the dinosaurs. 



Questions 



1. List five differences in physical conditions between the aquatic and terrestrial en- 

 vironments to which terrestrial vertebrates had to adapt. 



2. In what ways were crossopterygians preadapted to a terrestrial life? What other con- 

 ditions favored crossopterygians in making the adaptive shift from water to land? 



3. In what ways have aijiphibians successfully adapted to the terrestrial environment? 

 In what ways are they poorly adapted for life on land? 



4. List and give the distinguishing characters of the orders of living amphibians. 



5. Which salamanders do not have lungs? How do these salamanders respire? 



6. What features of toads enable them to li\e in drier environments than frogs? 



7. In what ways are the embryos modified in frogs that have a direct development? 



8. Under what environmental conditions have the larval stages of frogs been suppressed? 

 Is it possible that similar conditions played a role in the evolution of terrestrial re- 

 production in the ancestors of reptiles? 



9. In what ways are reptiles better adapted for terrestrial life than amphibians? 



10. List the extraembryonic membranes of a reptile einbryo and briefly state the func- 

 tion of each. 



11. Define a cleidoic egg. 



12. Which groups of vertebrates are amniotes; which are anamniotes? 



13. What were the earliest reptiles? 



14. Name two groups of Mesozoic reptiles that returned to the sea and l)ecame very 

 well adapted to the marine environment. 



15. How can one distinguish a legless lizard from a snake? How can one distinguish a 

 lizard from a salamander? 



16. Which group of living reptiles is most closely related to the dinosaurs? 



17. Which group of reptiles gave rise to the mammals? 



Supplementary Reading 



A great deal of interesting information on amphibians and reptiles can be found in 

 the general references for vertebrates cited at the end of Chapter 22. An invaluable addi- 

 tional reference on the classification, anatomy, physiology and habits of amphibians is 

 Noble's Biology of the Amphibia. The many fascinating adaptations of amphibians and 

 reptiles have been discussed by Barbour, Reptiles and Amphibians. There are many good 

 accounts of the United States species of amphibians and reptiles and their natural his- 

 tory. Among those of value to specialist and general reader alike are: Wright and Wright, 

 Handbook of Frogs: Bishop, Handbook of Salamanders; Carr, Handbook of Turtles; 

 Smith, Handbook of Lizards; Schmidt and Davis, Field Book of Snakes. 



