354 A HISTORY OF FISHES 



over the world, and were represented by a large number of 

 species and individuals. The fact that during the Devonian 

 period these groups were already represented by several diverse 

 forms, suggests that the Pisces had had a long history, even at 

 this time, and had undergone considerable differentiation. 



The earliest members of the Palaeopterygii were a family of 

 fishes known as Palaeoniscids, which had their beginnings in 

 the Lower Devonian, attained their maximum development 

 during the Carboniferous and Permian periods, and finally 

 became extinct towards the end of the Jurassic. They ranged 

 over the major part of the globe, fossil remains having been 

 found in the British Isles, various parts of Europe, South Africa, 

 Australia and North America. The Palaeoniscidae exhibit such 

 a combination of what may be regarded as primitive features 

 that they may be looked upon as the ancestors of all other 

 Bony Fishes, with the exception of the Crossopterygians. They 

 are mostly elongate fishes, fusiform in shape, with a large 

 heterocercal tail and a single dorsal fin (Fig. 127A). The body 

 is ensheathed in a complete armour of small, closely fitting, 

 diamond-shaped, ganoid scales, the shining surfaces of which 

 are often elaborately sculptured; the head is protected by a 

 series of bony plates. The mouth is rather large, and usually 

 armed with sharp, pointed teeth, while above it projects a short 

 and blunt snout. From their general build there can be little 

 doubt that some of these were fast-swimming, predaceous fishes. 



During the Carboniferous period a branch of the Palaeoni- 

 scids gave rise to the Platysomidae, which flourished with them 

 until late Permian times. They are of very diflferent shape, 

 with a deep, compressed body, larger dorsal fin, smaller mouth 

 and blunt, crushing teeth : the scaly covering of the body is still 

 of the ganoid type (Fig. 12 73). These fishes held their own 

 for an enormous period of time, but their record is actually 

 a shorter one than that of the parent stock from which they 

 sprang, and they do not appear to have given rise to any later 

 forms. Another oflfshoot (Catopteridae) from the Palaeoniscids 

 during the Triassic period, are small fishes found in the rocks 

 of North America, Europe, Africa, and Australia. The same 

 ganoid armour still persists, but the upturned end of the tail is 

 very much shorter. The Belonorhynchidae also arose from the 

 main stem during this period, and these are characterised by 

 the very long snout and lower jaw, and by the disappearance 

 of nearly all the ganoid scales, which are replaced by four rows 

 of scutes running along the body, rather like those of the existing 



