Fossil Plants are generally Carboniferous in age or younger. Some of the most common types of fossil plants include ferns, horsetails, and club mosses. At the end of the Carboniferous, the tree-shaped clubmosses and horsetails declined, mainly because the swamps were disappearing and because it became colder on Earth. Still, there were some coal swamps in the earliest part of the Permian. In that region coal seams combined with plant layers and root, layers have been formed in the same way as the Carboniferous.