228 TEN years' progress in vertebrate paleontology 



marvelously perfect conditioii of preservation is present in special struc- 

 tures, and is most encouraging to the student who wishes to base his 

 conclusions on something more than scales, teeth, and hones. Thus, in the 

 small ganoid Rhadinichthys deani Eastman, from the Lower Carbonif- 

 erous of Kentucky, one. may examine (Parker) "indubitable remains of 

 the actual brain, internal ears, nerve endings and bloodvessels," and from 

 such intimate structures attempt detailed comparisons with modem forms. 



MESOZOIC AND CENOZOIC FISHES 

 BY C. R. EASTMAN 



Among the more important general results that have been gained 

 during the last decade from a study of the several piscine faunas occur- 

 ring throughout the Mesozoic and Cenozoic eras, the following are worthy 

 of attention : 



With the advent of the jMesozoic, that is to sa.}^, in the early Trias, 

 fishes of a higher grade in the scale of progressive evolution make their 

 appearance than those which were dominant during the Paleozoic. 

 Among Actinopterygian fishes the ancient race of Paleoniscids continues, 

 it is true, but the group is marked by degeneracy in the direction of 

 modern sturgeons, and the incoming Protospondvli of the Trias develop 

 a number of series, which in the fullness of time become molded into 

 the characteristic types of Upper Cretaceous and Tertiary fishes, in the 

 end becoming transformed into our present-day fauna. 



These large-mouthed Protospondyli with conical teeth, which are 

 traceable from the Trias onward until they pass almost imperceptibly 

 into modern bony fishes, constitute at least three important families — the 

 Eugnathidge, Amiidne, and Pachycormidae. It is interesting to note that 

 the last mentioned of these is represented in the Alpine Middle Trias by 

 the genus Urolepis, which shows considerable resemblance to the Paleo- 

 niscids. The Pacycormidae in particular show distinct evidence of grad- 

 ual progression as they are traced upward in their geological range. 



During the Jurassic the nexl higher suborder appears, that of the 

 Isospondyli, characterized by a simplified mandible and a more com- 

 pletely ossified internal skeleton. The teleostomes which acquire this 

 new and advanced t3'pe of skeletal frame soon give rise to a varied series 

 of families and begin to predominate in the Cretaceous ichthvic fauna. 

 Until this time, as remarked by one of our foremost authorities on pale- 

 ichthyology, Dr. A. Smith Woodward, "the skull of the Actinopterygii 

 had always been remarkably uniform in tvpe, . . . the pelvic fins 



