Mean atmospheric O2
Geologic Time Scale
A massive, 30-ton ichthyosaur of the genus Shonisaurus, the largest known marine reptile, attempts to make a meal of a school of squid-like order of cephalopods known as belemnites 230 million years ago. On the far right is a prehistoric shark, and further below is an ancient Ammonite, another squid-like animal with a nautilus-like hard shell.
Panthalassa, the vast global ocean that surrounded the supercontinent Pangaea, was home to the ichthyosaurs, giant air-breathing reptiles that resembled fish and dolphins. Like modern day cetaceans, ichthyosaurs are believed to have evolved from land reptiles that moved back into the water. Ichthyosaurs are notable for having the largest eyes of any land or sea animal. The eye socket of one fossil Shonisaurus skull is over 3 feet in diameter.
Copyright © Walter B. Myers. All rights reserved.
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