Mean atmospheric O2
Geologic Time Scale
Calamites & Drepanophycus
Arborescent (tree-like) horsetails of the genus Calamites of varying size (10 to 50 feet tall) populate lowlands near the brackish waters of an inland sea 390 million years ago. Closer to the ground at about 6 feet tall is a variety of Drepanophycus, a genus of the division Lycopodiophyta, ancient plants that preceded the Calamites by about 20 million years and coexisted with them for 35 million years.
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