Mean atmospheric O2
Geologic Time Scale
Calamites & Asteroxylon
This is how a forest of arborescent (tree-like) horsetails of the genus Calamites and Asteroxylon, a genus of the division Lycopodiophyta, may have appeared just about anywhere on the Earth 390 million years ago. The Calamites are the slender "Christmas tree" shaped plants. They grew as tall as modern conifers, though they are the ancient ancestors today's much smaller horsetails. The snake-like curlicue plants in the foreground are the now-extinct Asteroxylon, which emerged at the beginning of the Devonian period about 417 million years ago.
Copyright © Walter B. Myers. All rights reserved.
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