848 



THK AMKh'JC.W X Air h'A LIST 



[\ OL. XL 



climatic change modifying even a comparatively limited area 

 would suffice to sweep them out of existence." 



In the summary of the tooth characters of the Titanotheres 

 we have shown how Nature was ai)parently making an effort 

 to develop a long or hypsodoiit crown by the elongation of the 

 ectoloph on the outer side of the superior grinding teeth, and 

 secondly how this effort was apparently futile })ecause of the 



and the al)scnce of a transverse crest. Such a tooth is half hy|)so- 

 dont and half brachyodont. It does not favor longevity l)ecause 

 it is soon worn off. 



A cul de sac in evolution is an avenue from which thei'c is no 

 escape. This was reached in the teeth of the I'itanotheres not, 

 as in many other animals by a great sacrifice of numbers in the 

 specialization of the teeth, but by a sacrifice of part.s-\ tiie inter- 

 mediate tni)er( les were lost and the internal tubercles were isolated. 

 It is noteworthy that every animal ex[)erimenting with teeth of 

 this kind u\nopl(.rl.eriida>. Anthracotherii.hv, ( "lialicotherii(he) 

 became extinct; tluM'c was no further mechanical iH-oo-ress or 



list record the 

 assed through 



walevsky's 



