MODIFIED HOMOCERCAL 



FIERASPIS 

 GEPHYROCERCAL 



Figure 6-42. Evolution of toil fins in fishes. 



of the originally heterocercal tail; this is also an abbrevi- 

 ated homocercal type. 



In the dipnoans the tail ranges from that of the living 

 lungfishes, a protocercal type ( prolos — first, primary) in 

 which the ray-supported part of the fin is limited to the 



margins, back in time to the heterocercal tail of Dipterus or 

 the protocercal tail of Phaneropleuron, which has a separate 

 anal, or Uronemus. Among crossopterygians there are those 

 which are diphycercal {diphyes — double) or modified diphy- 

 cercal (Eusthenopteron), but most are heterocercal. Actinis- 



MEDIAN FINS 



169 



