X 



LUNG-FISHES 



1. Classification 



Class Crossopterygii 

 Order i. Rhipidistia. Devonian-Recent. 



Suborder i. *Osteolepidoti. Devonian-Carboniferous 



*Osteolepis; *Sauripterus; *Diplopterax; *Eiisthenopteron 

 Suborder 2. Coelacanthini (= Actinistia). Devonian-Recent 

 *Coelacanthus; *Undina; Latimeria 

 Order 2. Dipnoi. Devonian-Recent. 



*Dipterus; *Ceratodns; Neoceratodas; Protopterus; Lepidosiren 



2. Crossopterygians 



Although the lung-fishes and their allies are here considered last of 

 all the groups of fishes, because they lead on to the amphibia, it is 

 important to realize that in many features they stand close to the 

 ancestral stock of gnathostomes. It is a mistake to consider them as 

 'higher' animals than, say, the elasmobranchs or actinopterygians. 

 Only four genera belonging to this group are found at the present 

 time, Neoceratodus, Lepidosiren, Protopterus, the lung-fishes of Aus- 

 tralia, South America, and Africa respectively, and Latimeria, recently 

 discovered off the east coast of South Africa and the Comoro Islands 

 off Madagascar. These are relics of a group that can be traced back 

 with relatively little change to the Devonian, and there is little doubt 

 that at about that period the first amphibia arose from some similar 

 line. The characters of the modern crossopterygians are therefore of 

 extraordinary interest, because they show an approach to the condition 

 of the ancestors of all tetrapods. 



3. Osteolepids 



Osteolepis itself (Fig. 161), from the middle Devonian, was the 

 earliest and most primitive member of the group. In appearance it 

 shows an obvious similarity both to palaeoniscids and to early Dipnoi 

 and it was probably close to the line of descent from some placoderm 

 ancestor to both of these groups and to the amphibia. The body was 

 long and the tail heterocercal. A feature distinguishing all early Cros- 

 sopterygii from early Actinoptergyii was the presence of two dorsal 



