No. 480] 



EXTINCTION or MAMMALIA 



857 



In 1884 Marsh briefly considered tlie brain question in relation 

 to the extinction of the Titanotheres or Brontotheriidae. He ob- 

 serves (p. 190): "The small brain, highly specialized characters, 

 and huge bulk, rendered them incapable of adapting themselves 

 to new conditions, and a change of surroundings hrought extinc- 

 tion/" Again ip. !<)()): "The Dinocerata, with their vcrv (hniinu- 

 tive brain, fixed characters, and massive frames, tlonri^hed as 

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

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

 discussing the brain, especially after referring to the general law 

 of brain growth (?, e., evolution) during the Tertiary period, he 



"To this general law of brain growth two additions may now be 

 made, which briefly stated are as follows: (1.) The brain of a 

 mammal belonging to a vigorous race, fitted for a long survival, 

 is larger than the average brain, of that period, in the same gionj). 

 (2.) The brain of a mammal of a declining race is sniaUer than 

 the average of its contemporaries of the same group." ^ 



As above noted the chief advantages of brain capacity are un- 

 doubtedly in relation to adaptability of habit, resourcefulness in 

 times of exposure, alertness in avoiding new dangers to which the 

 young may be exposed, enterprise in seeking new habitat, quali- 

 ties which should be more fully consichM'ed undtM- (he law of adap- 



