16 HOMOIOTHERMISM 



spelled the doom of the overgrown and specialized Rep- 

 tilia of the Mesozoic/' A giant dinosaur required tons 

 of plant food, while a small mammal subsisting on seeds 

 and fruits could remain active at all seasons. The de- 

 velopment of seeds and fruits greatly increased the food 

 resources of early mammals. Berry stresses the fact 

 that differentiation among the flowering plants was soon 

 followed by the great differentiation of mammals, be- 

 ginning in the Eocene Period. 



