Though today's living reptiles are highly diverse and hold a wide range of niches, the reptilia of yesteryear were even more prolific. The Mesozoic wasn't dubbed the age of reptiles for nothing. They lived in the air and the sea, on land, in trees and underground. Not only did they occupy most of the niches that they do today, but most of the niches that mammals and birds hold now, along with a few niches that are left totally empty today. Click on the link below to see the reptile group of your choice.