THE ALLIES OF THE PERCH: PISCES 325 



to the latter part of the Age of Invertebrates, are represen- 

 tatives of the sharks and rays, lung-fishes, and, among the 

 bony fishes, forms related to the garpikes of to-day. Thus 

 all the great groups of fishes were in existence very early, 

 with the single exception of the most specialized bony fishes, 

 of which the perch is an example. Fig. 162 shows two spe- 

 cies of Devonian fishes. 



The earliest fossil remains of the sharks and rays are frag- 

 ments of teeth and spines, for the skeleton was not fully 

 ossified and no coat of mail was developed. The shark-like 

 forms rose to great prominence in the course of the Age 

 of Fishes, a little later becoming the predominant type of 

 fishes, of which our species to-day are but the scattered rem- 

 nants. The sharks are especially interesting in that they 

 probably represent most nearly the ancestral condition of 

 all fishes, and hence of all animals with a back-bone. The 

 rays are more modern descendants of the group, adapted to 

 life on the bottom. 



The lung-fishes were also a dominant group very early in 

 the period. By the end of the next succeeding age they had 

 practically disappeared, leaving, as has been noted, but few 

 descendants to-day. Some of them, which have been found 

 in the rocks of Ohio, were giants among fishes ; they were 

 covered with great plates, at least anteriorly, and ranged in 

 length from ten to twenty-five feet. 



Among the gar-forms there are many well-preserved speci- 

 mens, owing to the fact that these fishes were incased in a 

 complete coat of mail formed of closely interlocking bony 

 plates, such as those found in the gaipike and, in vestigial 

 form, in the sturgeon of to-day. 



The other bony fishes, forming ninety-five per cent of all 

 the species of fishes to-day, may well be called modern fishes, 

 since they did not make their appearance till long afterwards, 

 in the Age of Reptiles. 



