Biographical Sketch 9 



taught this subject at Bellevue Medical College and it is known that many years later 

 he still took a lively interest in it. 



RESEARCHES AT COLUMBIA UNIVERSITY 

 1890-1912 



We do not know under what circumstances this eager brilliant youth came under 

 the influence of the famous geologist, Professor John Strong Newberry. But it is a matter 

 of record that after entering Columbia University as a graduate student in geology and 

 biology, he became at first instructor in geology and was soon associated with Pro- 

 fessor Newberry in the latter's studies on the fossil fishes of the Devonian of Ohio. 



STUDIES ON THE DEVONIAN PLACODERMS 

 1890-1909 



His doctor's dissertation, 'Tmeal Fontanelle of Placoderm and Catfish" (1891), was 

 richly illustrated with his own drawings; in it the histology and anatomy of the pineal 

 organ in recent vertebrates were thoroughly explored, and much new light was shed 

 upon the probable function of the so-called pineal funnel in the top of the skull of 

 Dinichthys and other armored fishes of the Devonian period. The long prevalent but 

 erroneous view that the catfishes were somehow an extraordinarily ancient offshoot from 

 near the base of the true fishes was accepted in this paper for what seemed to be at the 

 time good and sufficient reasons. 



His subsequent papers on the structure and classification of these enigmatical placo- 

 derms and their allies numbered a dozen or more and ranged from 1893 to 1909. They 

 contributed greatly to the necessary facts of the case and led him to the interesting view 

 that the arthrodires and their allies were neither peculiarly specialized dipnoans as held 

 by Eastman and others, nor modified crossopterygians as suggested by Tate Regan, but 

 that they were a wholly independent class of chordates that merely paralleled the other 

 fishes without being nearly related to them. On the other hand, both Dean and his 

 assistant Dr. L. Hussakof believed that the arthrodires might be an offshoot from the base 

 of the stem leading to Ptenchthys. While studies by Stensio, on the distribution of the 

 vascular and neural canals and on brain casts of early arthrodires, indicate a somewhat 

 nearer relationship to the elasmobranch stock than Dean suspected, the other connection, 

 with the stem of Ptenchthys still appears highly probable. 



STUDIES ON DEVONIAN SHARKS AND THE ORIGIN OF PAIRED FINS 



1893-1909 



Dean's studies on the Devonian sharks, also beginning while he was an assistant to 

 Professor Newberry, led to a far reaching contribution to the problem of the origin and 

 evolution of the paired appendages of vertebrates. In 1893 when 26 years of age he con- 

 tributed his first "Note on the Mode of Origin of the Paired Fins"; he dealt also with 

 various phases of this topic in many subsequent papers. His Devonian Cladodont shark, 

 Cladoselache newberryi which he first described in 1893, showed that the paired fins were 



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