390 \V. D. MATTHEW THE CRETACEOUS-TERTIARY PROBLEM 



Fam. ? Epanorthidae 



Picrodus silberlingi. (Family position doubtful, as this family is 

 unknown outside of South America. Possibly a Multituberculate 

 of undescribed family) 

 Order Insectivora 

 Fam. incert. 



Coriphagus montanus 

 Megapterna minuta 

 Fam. ? Mixodectidse 



f Mixodectes sp. (Not Mixodectidae ; doubtfully Insectivore) 

 Order Oarnivora (Ferse) 

 Fam. Oxyclaenidse 



Protochriacus sp. (Reference questionable) 

 ? Chriacus sp. (Not figured; of no value in correlation) 

 f Tricentes sp. 

 f Deltatherium 

 Order Taeniodonta 



Fam. Stylinodontidae 



Calamodon sp. (Agrees better with Psittacotherlum) 

 Order Condylarthra 



Fam. Phenacodontidae 



Euprotogonia (= Tetraclsenodon) sp. 

 Fam. Mioclaenidse 

 Mioclwnus sp. 

 Order Taligrada 



Fam. Pantolambdidse 



Pantolarnhda sp. 

 Fam. Periptychidae 

 Anisonchus sp. 



Interpretation of the Vertebrate Faunas 



T\\Q evidence of fossil vertebrates in correlation is very valuable, pro- 

 vided it is interpreted correctly. Owing to the complex structure of the 

 liard parts preserved and their capacity for relatively rapid and extreme 

 progressive and adaptive changes in these hard parts, they afford a more 

 precise and exact measure of time than do any other animals. This is 

 peculiarly true of the mammals; dinosaurs, perhaps, rank next; other 

 vertebrates are much less progressive. But as they respond more quickly 

 to the opportunities for evolution afforded by lapse of time, so also they 

 are more sensitive to difference of environment and more subject to 

 (;hange of geographic range and great migration movements, conditioned 

 by great environmental changes in other regions. Moreover, the evidence 

 is often fragmentary, and the reference of recol-ded genera and species 

 doubtful and provisional to a varying degree. Omitting this element of 

 doubt, the difference between two vertebrate faunae may be due to 



