AMERICAN ZOOLOGISTS AND EVOLUTION. in 



" On Critical Periods in the History of the Earth and their Relation 

 to Evolution : and on the Quaternary as such a Period," may be 

 found an excellent rejoinder of Professor Clai-ence King's lecture be- 

 fore the Sheffield Scientific School on the subject of " Catastrophisra 

 and Evolution." 



Among the most interesting discoveries connected with these 

 creatures is the determination by Professor Marsh * that these early 

 mammals, birds, and reptiles had brains of diminutive proportions. 

 He says in regard to the order Dinocerata, a group of gigantic mam- 

 mals whose remains have been found in the tertiary deposits of the 

 Rocky Mountain region, that they are the most remarkable of the 

 many remarkable forms brought to light. The brain of these creat- 

 ures was remarkable for its diminutive proportion. So small, indeed, 

 was the brain of Dinoceras mirahile, that it could " apparently have 

 been drawn through the neural canal of all the presacral vertebra." 

 In alluding to the successive disappearance of the large brutes, the 

 cause is not difficult to find : " The small brain, highly specialized 

 characters, and huge bulk, render them incapable of adapting them- 

 selves to new conditions, and a change of surroundings brought ex- 

 tinction. The existing proboscidians must soon disappear, for similar 

 reasons. Smaller mammals, with larger brains, and more plastic 

 structure, readily adapt themselves to their environment, and survive, 

 or even send off new and vigorous lines. The Dinocerata, with their 

 very diminutive brain, fixed characters, and massive frames, flourished 

 as long as the conditions were especially favorable ; but, with the first 

 geological change, they perished, and left no descendants." Professor 

 Marsh says that the brain of Dinoceras was in fact the most reptilian 

 brain in any known mammal. 



Professor Cope,f in describing the brain of Coryphodon from the 

 deposits of New Mexico, says : " The large size of the middle brain 

 and olfactory lobes gives the brain as much the appearance of that of 

 a lizard as of a mammal." This is one of the lowest mammalian 

 brains known. There are others from the Lower Eocene with equally 

 low brains as Arctocyon of Gervais and Uintatherium of Marsh. Cope 

 believes that the type of brain of these early creatures is so distinct 

 as to necessitate the erection of a third sub-class of equal rank with 

 the groups Gyrencephala and Lycencephala, which he would define as 

 the Protencephala. He shows their approximation to reptiles. 



Cope J refers to Gratiolet as showing that a great development of 

 the olfactoiy is a character of an inferior type ; in fact, the more we 

 ascend into paleontological antiquity, the more we find that the olfac- 

 tory lobes display a greater development in comparison with the cere- 

 bral hemispheres. Dr. B. G. Wilder* has shown that in the lamprey 



* "American Journal of Science and Arts," vol. xxix, p. 173. 



f "American Naturalist," vol. xv, p. 312. % "National Academy of Sciences," 1876. 



* " American Journal of Science and Arts." 



