670 - Heredity and Evolution 



Fig. 32-40. A lung fish (Dipnoi) being removed from 

 cake of mud in which it was shipped from Africa. 

 (Copyright, General Biological Supply House, Inc.) 



lar connection with the pharynx and dis- 

 plays a lunglike structure. Such "lungs," in 

 fact, are able to carry on respiration during 

 periods when ihese creatures are left stranded 

 in mud at the bottom of a dried-up pond or 

 lake (Fig. 32-40). 



One virtually extinct group of bony fish 

 (the Crossopterygii, or lobe-finned fishes) are 

 of particular interest because they gave rise 

 to the Amphibia. These fish tend to resemble 



Amphibia, especially as to the pattern of the 

 skull bones, the arrangement of the fin bones, 

 and the structure of the teeth. For many years, 

 the lobe-finned fish were considered to be 

 completely extinct. But in 1938, off the coast 

 of South Africa, a five-foot coelacanth (one 

 of the crossopterygian orders) was caught at 

 a depth of about 250 feet by a commercial 

 trawling vessel. And since then the fisher- 

 men of that general region, stimulated by 

 generous rewards offered by museums, have 

 succeeded in catching three or four more 

 specimens (Fig. 32-41). 



The Amphibia. Three groups of modern 

 Amphibia have been evolved: (1) the Uro- 

 dela— salamanders, newts, mud puppies, and 

 other Amphibia having a distinct tail; (2) 

 the Anura — frogs (Fig. 32-39), toads, and 

 other forms that do not have tails; and (3) 

 the Apoda, a very small group of limbless, 

 burrowing Amphibia, with elongate cylin- 

 drical, wormlike bodies. 



The ancient Amphibia became extremely 

 abundant during the Permian and Triassic 

 periods. These early forms, in fact, were the 

 first vertebrates to invade the land environ- 

 ment. The Amphibia, accordingly, display a 



Fig. 32-41. Model of Latimeria, the only surviving representative of the ancient lobe-finned fishes. These cross- 

 opterygians, which were very abundant 75 million years ago, were believed to be extinct, until quite recently. 

 Since 1938, however, several specimens of this fish have been caught in deep water off the coast of South Africa. 

 (Courtesy of the American Museum of Natural History, New York.) 



