The Evolution of Fishes 



439 



Dr. Woodward observes: 



"As soon as fishes with a completely osseous endoskeleton 

 began to predominate at the dawn of the Cretaceous period, 

 specializations of an entirely new kind were rapidly acquired. 

 Until this time the skull of the Actinopterygii had always been 

 remarkably uniform in type. The otic region of the cranium 

 often remained incompletely ossified and was never prominent 



Fig. 2.50. — A living Berycoid fish, Paratrachichthys ■proathemuis Jordan & 

 Fowler. Missiki, Japan. Family Berycidcc. 



or projecting beyond the roof bones; the supraoccipital bone 

 was always small and covered with the superficial plates; the 

 maxilla invariably formed the greater part of the upper jaw, 

 the cheek-plates were large and usually thick; while none of 

 the head or opercular bones were provided with spines or ridges. 

 The pelvic fins always retained their primitive remote situation, 

 and the fin-rays never became spines. During the Cretaceous 

 period the majority of the bony fishes began to exhibit modifi- 

 cations in all these characters, and the changes occurred so 

 rapidl}^ that by the dawn of the Eocene period the diversity 

 observable in the dominant fish-fauna was much greater than 

 it had ever been before. At this remote period, indeed, nearly 

 all the great groups of bony fishes, as represented in the exist- 

 ing world, were already differentiated, and their subsequent 

 modifications have been quite of a minor character." 



