444 VERTEBRATE LIFE AND ORGANIZATION 



v*^ 





Figure 22.14. Laliineria, a living coelacanth found off the coast of the Comoro 

 Islands. (From Millet.) 



Both crossopterygians and lungfishes were successful in the fresh 

 waters of the Devonian, but have dwindled to a few relict species today. 

 Lungfishes retained their lungs and have survived in the unstable fresh- 

 water environments of tropical South America, Africa and Australia. It 

 was long believed that all crossopterygians had become extinct, as indeed 

 the primitive fresh-water ones have. However, a few specimens of a 

 soinewhat specialized side branch (the coelacanths) have been found in 

 recent years near the Comoro Islands between Africa and Madagascar 

 (Fig. 22.14). Their internal anatomy is being studied carefully by Pro- 

 fessor Millot of Paris, who has several well preserved specimens at his 

 disposal, and we should soon know more about the structure of these 

 interesting creatures. 



Questions 



1. How do homologous organs differ from analogous organs? Can it be assumed that 

 organisms having homologous organs are closely related? 



2. What factors prevent the fossil record from giving us a complete and unbiased picture 

 of the life of the past? 



3. Briefly describe the general nature and mode of life of the ostracoderms. What 

 living vertebrates are most closely related to them? 



4. What were the major evolutionary advances of the placoderms? 



5. How do members of the class Chondrichthyes differ from members of the class 

 Ostcichthyes? 



6. How have a typical shark, a whale shark, a skate and a sawfish diverged in their 

 method of feeding? 



7. Under what conditions did lungs probably evolve? Is the swim bladder more primi- 

 tive than lungs? 



8. How do actinopterygians differ from sarcopterygian fishes? 



9. What morphologic changes occurred during actinopterygian evolution? 



10. From which group of fishes did tetrapods evolve? 



11. Define and give an example of adaptive radiation. 



12. Define and give an example of convergent evolution. 



