The warm and humid Carboniferous period (286-363 MYA) saw the global explosion of a new kind of ecosystem. Great swamps spread over much of the land and giant trees towered over the dense vegetation. Dead plants formed a layer of wet peat, which eventually became coal.

Carboniferous coal often contains the fossils of leaves, trunks, roots and fruit. Many of these come from a tree called Lepidodendron, which could grow as high as 50 metres in just a few years. Different parts of the tree have different latin names because they were originally thought to belong to different species. The cones are called Lepidostrobus and the thick root-bearing branches at the base are called Stigmaria. The trees' great height enabled them to catch sunlight way above the shorter plants, but also made them rather precarious. Fully grown trees toppled over and added to the swamp.

Arthropods like Acantherpestes, the giant millipede, fed on the decomposing plant debris. Some of its relatives also reached gigantic size - 90cm(inch)-long scorpions and enormous dragonflies also lived in the forests.