434 ELEMENTARY GEOLOGY 
Age of Mammals. The lower types, which began in 
the Mesozoic, little by little diminished in variety and 
Fig. 253. 
Marsh’s restoration of flying reptile. 
importance, and their place is taken by the higher 
forms of mammals. At first these were large species 
(Plate 21); but as time pro- 
gressed, the size diminished, 
until at present large mam- 
mals are the exception. 
During the Tertiary, many 
species as large as the ele- 
phant were in existence. 
If we could have had a 
view of the land during the 
mid-Tertiary time, we would 
have seen very little differ- 
ence between the life of 
that period and the present. 
Fic, 254. 
Ichthyornis victor. A bird with teeth. There would be many trees, 
(Cretaceous. ) flowers, insects, birds, and 
mammals which were strange to us, but the general 
