1 66 



TELEOSTOMES 



what seem to have been their primitive structural condi- 

 tions. Their skeleton has become highly calcified, its ele- 

 ments multiplying, fusing, and specializing. The notochord 

 has practically disappeared, owing to the complete formation 

 of bony vertebrae. The derm bones of the head, which in 



Ancestral 

 Teleostome 



(TABLE IV) 



Palaeozoic 



CROSSOPTERV^IAN 



PAUAeozoic 

 palaeoniscoio 



Mesozoic 



Ganoid 



_— Mesozoic 



Caturio 



Sturgeon. \ i w \ \ \\\\\\\\ 



LEPIDOSTEUS SlLUROlD I Physostome WWWW ^°P"°Branch 



POL.YPTERUS AmiA AcANTHOPTERYGIAN 



Fig. 171 A. — The Phylogeny of the Teleostomes. 



Syngnath 



the ancestral Ganoid were at the surface, enamel-coated,* 

 are now deep-seated in the head, resembling true cartilage 

 bones ; their surfaces are usually deeply furrowed or ridged, 



* The enamel of Ganoid plates (ganoine) appears to be derived from the 

 underlying bony tissue, not deposited by the overlying epidermis (enamel 

 organ). 



