THE DEVONIAN PERIOD 



367 



FIG. 382. Unsymmetrical tail of 

 the sturgeon, in which the body 

 axis follows the upper blade of 

 the fin. 



on the other hand, had fully 



vertebrated fins (Figs. 381 and 



382). Again, there are some 



very peculiar things about the 



teeth of these ancient members 



of the finny tribe. Unlike the 



sharp, spikelike teeth of modern 



fishes (Fig. 385), many of them 



were rounded or corrugated 



plates (Fig. 384) adapted for grinding 

 food rather than for seizing live prey. 



Altogether the De- 

 vonian fishes were 

 massive and clumsy. 

 As in the arthropods, 

 their skeletons were FlG . 384 . _ A single 

 chiefly on the outside 

 in the form of bony 

 armor, for the limb 



tail fin characteristic bones and Spinal Col- 

 of the higher types of umn were often little 



than cartilage. 



corrugated tooth of 

 a Devonian shark- 

 like fish. 



FIG. 383. Fan-shaped 



fishes. 



more 



As time went on, the advantage of speed -p IQ 335. Pointed 

 over armor seems to have led to the tooth of an extinct 

 strengthening of the internal skeleton with 

 bone, and to the development of a more flexible body. 



FIG. 386. A modern lung fish from Australia, not unlike certain Devo- 

 nian fishes. 



LIFE ON LAND 



For the first time we have among the Devonian fossils a 

 fair representation of the animals and plants of the lands. 



