40 THE ORIGIN OF MAN 



were also many bryozoans, but the crinids were 

 far less abundant. The blastids and starfishes 

 were also abundant, likewise the trilobites, but 

 which were very greatly reduced in variety. The 

 fishes of this time were primitive in that they 

 did not have well developed internal skeletons 

 and in that they were more cartilaginous than 

 bony. The median fins were often continuous, 

 or a series of fins, extending along the dorsal and 

 ventral surfaces and meeting around the end of 

 the tail. The vertebral column often extended 

 to the end of the tail, with the continuous fin all 

 around it, a type of tail (diphycercal), nearly 

 always present in the earliest stages of modern 

 fishes. Of vertebrates higher than the fishes it is 

 thought that there existed a salamander-like ani- 

 mal with a probable length of nearly three feet. 

 As we are about to enter the Late Paleozoic 

 era it will be best for us to make a brief resume of 

 fishes, as fishes are very important in the evolu- 

 tion of animal life being the first vertebrates. 



