PRE-CAMBRIAN AND PALEOZOIC ERAS 161 



"It is plain that the fish can crawl about, in the water at least" (Smith, 

 1956). 



The Crossopterygii gave rise to the first amphibians, the labyrinthodonts. 

 A few remains indicate that the transition occurred in the Devonian. 

 These first amphibians were long-bodied, weak-limbed creatures, some- 

 what "lizardlike" in appearance (Fig. 8.19). The lobe fins inherited from 

 their crossopterygian ancestors had been transformed to serve as supports 

 for the body in a medium, air, which did not buoy up the body as had 



cleiihrum 

 /Scapula 



scapula 



FIG. 8.18. Skeletal elements in the fin of the crossopterygian fish, Eusfhenopteron (left), 

 and in the limb of the Paleozoic amphibian, Eryops (right). H, humerus. R, radius. U, 

 ulna. (After Gregory; by permission from General Zoology, by Storer, p. 201. Copyright, 

 1943. McGraw-Hill Book Company, Inc.) 



the water of the old environment. Fig. 8.18 shows the skeletal elements 

 in a typical crossopterygian fin and in the hmb of an early amphibian. 



We may note in passing that the idea that Devonian Crossopterygii 

 used their fins to crawl out on land does not seem improbable in view of 

 the nature of the coelacanth fins and the fact that in certain parts of the 

 world today some fishes (e.g., "climbing perch") use their fins in just this 

 manner, even climbing trees in search of insects. 



The air bladder, inherited by amphibians from crossopterygian ances- 

 tors, served as simple lungs, and, as we have seen, the nostrils were ar- 

 ranged to permit breathing with the mouth closed. 



The labyrinthodonts retained many features of their crossopterygian an- 

 cestors. Their name refers to a complicated pattern of infolding which char- 

 acterized the arrangement of the enamel of the teeth. A similar arrange- 

 ment characterized the enamel patterns of crossopterygian teeth. The 



