438 



The Evolution of Fishes 



proaching the garpike and sturgeon. The Crossopterygians 

 rapidly decline. The Dipnoans are less varied and fewer m 

 number; the primitive sharks, with the exception of certain 

 Cestracionts, all disappear, only the family of Orodoniidw remain- 

 ing Here are found the first true bony fishes, doubtless derived 

 from Ganoid stock, the allies and predecessors of the great group 

 of herrings. Hernng-like forms become more numerous in the 

 Jurassic, and with them appear other forms which give the fish- 

 fauna of this period something of a modem appearance. In the 

 Jurassic the sharks become divided into several groups, Nottdani, 

 Scyllioid sharks, Lamnoid sharks, angel-fishes, skates, and finally 

 Carcharioid sharks being now well differentiated. Chimaeras are 

 still numerous. The Acanthodei have passed away, as well as the 

 mailed Ostrachopores and Arthrodires. The Dipnoans and 



Fig. 249. — Hoplopteryx lewesiensis (Mantell), restored, English Cretaceous. Family 

 Berycidce. (Aiter Woodward.) 



Crossopterygians are few. The early Ganoids have given place to 

 more modern types, still in great abundance and variety. This 

 condition continues in the Cretaceous period. Here the rays 

 and modern sharks increase in number, the Ganoids hold 

 their own, and the other groups of soft-rayed fishes, as the 

 smelts, the lantern-fishes, the pikes, the fiying-fishes, the berycoids 

 and the mackerels join the group of herring-like forms which 

 represent the modern bony fishes. In the Cretaceous appear 

 the first spiny-rayed fishes, derived probably from herring-like 

 forms. These are allies or ancestors of the living genus Bcrvx. 



