THE DEVONIAN PERIOD 



465 



predaceous creatures, but it is more probable that they lived on the 

 ocean bottom and subsisted largely on shellfish, using their powerful 

 jaws for crushing. With their heavy armor and clumsy shape they 

 were probably sluggish in their movements. 



(2) Unarmored Lungfish. — Another abundant group of lung- 

 fishes whose descendants have succeeded in living to the present 

 were unhampered by armor but were covered with thin scales (Fig. 

 442). A modern representative (Ceratodus) lives in Australian 

 waters, and two other genera are known, one in Australia and one in 

 South America. 



Ganoids. — (1) Fringed- finned Ganoids (Crossopterygians). — Evo- 

 lutionary, this is the most important of the Devonian fishes, since it 



Fig. 443. — A fringe-finned ganoid, Holoptychius. Some of these were four feet long. 



possessed so many characters in common with early amphibians 

 (p. 485) that it is probable that the latter arose from this order. 

 The fringe-finned ganoids had conical teeth generally fluted, were 

 covered with scales which were rhomboidal in some species and 

 rounded in others, and had limblike fins (Fig. 443) which were jointed 

 to the skeleton within the body. 



(2) Another order of ganoids (Actinopteri) may, for convenience, 

 be called typical ganoids to distinguish them from the fringe-finned 

 ganoids. These fishes, for the most part, had thick, rhomboidal 

 scales, such as those of their modern representative, the gar pike 



Fig. 444. — A typical ganoid, the modern gar pike. 



