Ask A Scientist© Biology Archive

Author:      tamar c
Text:        Why are today's land mammals so much smaller than prehistoric 
mammals?

Response #:  1 of 1
Author:      wizkid
Text:        Well, one possibility is due to competition for food.  Large 
animals need much more food than smaller ones to survive.  So, in times of 
food shortage, the large ones will not have enough to eat or will fight each 
other for what is available and tend to die off faster than the smaller ones 
which need relatively little to survive.  Another possibility:  availability 
of shelter.  Large animals have harder times finding shelter during storms, 
winter freezes, and other natural catastrophes, while smaller animals can hide 
much more easily.