372 Evolution and Distribution of Fishes 



CHAPTER XIII. 



The Evolution of Fishes. 

 (5) The Spine-Finned Teleostei. 



The observations already made (p. 348) as to our 

 preponderant knowledge regarding the occurrence and pre- 

 servation of marine over freshwater organisms during the 

 Cretaceous, applies also to a large extent, when we start 

 to trace the earliest reported occurrences of the spiny-rayed 

 teleosts or Acanthopterygii. But the writer trusts that, 

 by adoption of a process of comparison and elimination, he 

 may be able to set forth the correct main lines of their evo- 

 lution, and at least approximately when such took place. 



As a biological and ecological feature of great interest 

 also, he would recall Jordan's statement (p. 366) as to the 

 production of an increasing number of fin-spines in species 

 of Stickleback, as these pass from a freshwater to a marine 

 environment. For in this connection it may at once be said, 

 no matter how we may explain the fact, that in contrast to 

 the soft-rayed teleosts, which are largely freshwater, the 

 species of Acanthopterygii are largely marine. Further the 

 pelvic fins are subthoracic, thoracic to jugular in position, 

 and the air-bladder becomes usually a closed sac — specially 

 in types that remain freshwater, — or undergoes reduction 

 to final absorption as is largely true of marine types. 



Now, if the Teleostei are derived from a "ganoid" 

 or holostean ancestry, some connecting types must have 

 lived, or even may survive now, that are annectant in struc- 

 ture between the ganoids and typical Acanthopterygii, and 

 especially that show in combined relation, progressive for- 

 ward movement of the ventral or pelvic fins, gradually in- 

 creasing hardening of the dorsal and it may be the pelvic 

 and anal fin-rays, closure and even absorption of the air- 

 bladder, and gradual absorption of the mesocoracoid arch. 

 All of these requirements are satisfied in a set of living 

 fishes that comprise in progressive relation the Salmonldae, 

 the Percopsidae that Is made up of the two living genera 

 Percopsis and Columbia^ Aphredoderits that has been varl- 



