Mean atmospheric O2
Geologic Time Scale
A 40 foot long, seven ton coelurosaurian theropod dinosaur of the species Tyrannosaurus
rex wanders among oak trees and ground ferns 68 million years
ago on a Cretaceous island continent known as Laramidia in what is today the western United States.
On the lower left is a rodent-size proto-primate of the genus Purgatorius, and in the lower middle is an amphibious tetrapod of the family Salamandridae.
Copyright © Walter B. Myers. All rights reserved.
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