104 SECULAR TINGREASE IN SIZE CHAP. IV 
have left a dwarfish offspring; that. there were giants of 
old, and that there is a puny race to-day. As a matter of 
fact, the study of the gradual evolution of the early Tertiary 
Mammalia into their descendants of later times shows very 
plainly the truth of this interesting generalisation: That the 
primitive types were all small creatures, and that in those 
instances where we can trace a pedigree, there was a gradual 
increase in size up to a point where greater increase led to 
extinction. We point out later on a number of facts illus- 
trating this matter in detail. It has been ascertained, for 
instance, that the pedigree of the Horses, the Camels, the Rhino- 
ceroses, and many other groups, commences with small forms 
and culminates in large ones. It may be urged that such 
animals as the Tapir are to-day smallish forms, and that related 
to them in the past were the gigantic Titanotheres; but in this 
and similar cases it will be found that the extinct giants were 
not in the direct line of pedigree, but represented side-branches 
which waxed huge on their own account and then disappeared. 
