Mean atmospheric O2
Geologic Time Scale
Early Jurassic ammonite
A mollusk of the subclass Ammonoidea in a Jurassic sea 195 million years ago. This specimen's planispiral shell is about six inches in diameter.
Ammonites were plentiful in the Earth's oceans for about 400 million years becoming extinct, along with the dinosaurs, about 66 million years ago during the Cretaceous–Paleogene (K–Pg) extinction event. While resembling modern shelled nautiloids, these once plentiful mollusks are more closely related to living octopuses, squid, and cuttlefish.
Copyright © Walter B. Myers. All rights reserved.
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