172 THE ORIGIN AND EVOLUTION OF LIFE 



living starfishes, sharks are abundant, and arthrodiran fishes are 

 still abundant in Germany. 



It was long believed that the air-and-water-breathing Am- 

 phibia evolved from the Dipnoi, the air-breathing fishes of the 

 inland fresh waters, and this hypothesis was stoutly main- 



y -■-■ o* 



FIN STAGE 



RHIPIDISTIAN FISH 

 (DEVONIAN! 



FOOT STAGE 



AMPHIBIAN 

 (CARBONIFEROUS) 



Fig. 53. Change of Adaptation in the Limbs of Vertebrates. 



The upper figures represent the theoretic mode of metamorphosis of the fringe-fin of the 

 Crossopterygian lish (left) into the foot of an amphibian (right) through loss of the 

 dermal fringe border and rearrangement of the cartilaginous supports of the lobe. 

 After Klaatsch. 



The lower figures represent (left) the theoretic mode of direct original evolution of the 

 bones of the fringe-fin (A, B) of a Crossopterygian tish — the Rhipidistia type of Cope — • 

 into the bony, five-rayed limb (C) of an amphibian of the Carboniferous Epoch (after 

 Gregory); and (right) the secondary, reversed evolution of the five-rayed liml) of a 

 land reptile (.4) into the fin or paddle (B, C) of an ichthyosaur (after Osborn). 



tained by Carl Gegenbaur, who also upheld what he termed 

 the archipterygian theory of the origin of the vertebrate limb, 

 namely, that the prototype of the modern limbed forms of 

 terrestrial vertebrates is to be found in the fin of the modern 

 Australian lung-fish, Ccratodus. This hypothesis of Gegen- 

 baur, which has been warmly supported by a talented group of 

 his students, is memorable as the last of the great hypotheses 

 regarding vertebrate descent to be founded exclusively upon 



