SOME AMERICAN MONSTERS. 153 



In fact, it was a decidedly reptilian kind of brain. Perhaps it 

 may seem hardly credible, but so small was the brain of Dino- 

 ceras mirabile, that it could have been pulled through the 

 apertures (neural canals) of all the neck vertebra ! In certain 

 marsupials of the present day we find an approach to this kind 

 of brain. It seems to be an established fact, according to 

 Professor Marsh, that all the Eocene or earlier Tertiary mammals 

 had small brains. His researches among fossil mammals have 

 led him to the important conclusion that, as time went on, the 

 brains of mammals grew larger ; and thus he has been able to 

 establish his law of brain-growth during the Tertiary period, a 

 law which appears to be plainly recorded in the fossil skulls of 

 succeeding races of ancient mammals. The importance of a 

 discovery such as this cannot fail to strike the imagination of 

 even the most unlearned in geology as being singularly suggestive 

 and instructive. It is not difficult to picture these dull, heavy, 

 slow-moving creatures haunting the forests and palm jungles 

 around the margin of the great Eocene lake, into the waters of 

 which their carcases from time to time found their way — perhaps 

 swept down by floods. No footprints have been discovered 

 as yet. 



The Dinocerata were very abundant for a long time during the 

 middle of the Eocene period. The position of their remains 

 suggests that they lived together in herds, as cattle do now, and 

 they probably found an abundance of food in the shape of succu- 

 lent 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. Professor Marsh thinks that 

 from their sluggish nature they were incapable of adapting them- 

 selves with sufficient rapidity and readiness to new conditions, 

 such as may have been brought about by geographical changes. 

 It must be admitted, however, that the geological record in this 

 region does not give evidence of any sudden change. Possibly 

 they may only have migrated to some other region, where their 



