526 Evolution and Distribution of Fishes 



Detailed attention is given to the family Serranidae, 

 as being one that in part continued in freshwater, in con- 

 siderable part became marine; also to the Cichlidae that 

 attained to a special wealth of species and of structural 

 detail in Brazil. Then migrating across the S. Atlantis 

 land bridge into Africa, the latter evolved into the numer- 

 ous species that now inhabit the central African lake region. 

 Having reviewed the graded connections and evolutionary 

 sequence of the Percopsidae, Aphredoderidae, Percidae, 

 Centrarchidae, Serranidae, Cichlidae, Nandidae and deriva- 

 tive acanthopterous families, that largely remained in fresh- 

 water, or that sent small derivative outliers into the sea, 

 attention is next given to important families that became 

 wholly marine. Perhaps the most striking series is that 

 which, starting with Centrogenys of the Centrarchidae, or 

 possibly Etheostoma of the Percidae, underwent graded 

 condensation in body and mouth parts, also modification 

 and condensation with ultimate flattening in the teeth. So 

 through such families as the Pomacentridae, Labridae, and 

 Scaridae a transition is effected in marine types that exactly 

 simulates the change effected in the ganoid Pycnodonts al- 

 ready studied. The stages in their marine geographic 

 distribution are next traced, and thus a connected sequence 

 is established that parallels the morphological changes. 



The families Embiotocidae, Cobiidae, Echeneididae, also 

 the larger groups Scleroparei and Jugulares are then treated 

 of in their affinities, structure, and distribution, while the 

 aberrant Plectognathi are shortly studied. 



Chapter 14. Past Geographic and Geologic Conditions 

 in relation to the Distribution of fishes. 



Consideration is first given to possible changes that might 

 fundamentally affect groups of plants and animals. Fishes 

 are regarded as the most sensitive, responsive, and indi- 

 cative organisms for registration of such changes. So be- 

 ginning with existing conditions a graded backward review 

 is attempted. 



The relatively recent and evolved Acanthopterygii, sug- 

 gest in their marine, and still more fundamentally in their 

 freshwater distribution, the existence of a wide land bridge 



