258 EXTINCT MONSTERS 



succulent vegetation round the great lake. Geological evidence 

 points to their sudden extinction before the close of the Eocene 

 period ; but it is difficult to understand this. 



In the museum at Yale College are collected the spoils of 

 numerous expeditions to the West, and the many tons of bones 

 lying there are believed to represent the remains of no less than 

 two hundred individuals of the Dinocerata. So perfectly have 

 these bones been preserved by Nature that, even if the creatures 

 had been living now, the material for studying their skeletons 

 could hardly be more complete. Professor Marsh recognises 

 three distinct types in this strange group of quadrupeds, on each 

 of which a genus has been founded. The first and oldest form 

 is the Uintatherium, which takes its name from the Uinta 

 Mountains. This, as might be expected, is the most primitive 

 or least specialised form, and comes from lower strata. The most 

 highly developed or specialised form is the Tinoceras, and this 

 is found at the highest geological level or " horizon." 



Between these two extremes, and from an intermediate horizon, 

 comes the Dinoceras, 1 so that in tracing these animals through 

 the strata in which they occur the geologist finds that he is 

 following for a while the course of their evolution. Doubtless 

 there were many slight differences presented by the members of 

 this group, but at present it has not been found possible to 

 determine the number of species, although about thirty forms 

 more or less distinct have been recognised. Professor Marsh 

 says that the specimen of the skull of Dinoceras mirabile, on 

 which the whole order Dinocerata was founded, is, fortunately, 

 in a very perfect state of preservation, and that it belonged to 

 a fully adult animal. Moreover, it was embedded in so soft a 



1 The Dincoeras of Marsh is the same form as Eobasileus of Cope. Uinta- 

 therium was discovered by Leidy. 



