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Carboniferous · 358.9 – 298.9 Ma

Carboniferous fossil sites

Carboniferous coal swamps preserved entire forests of giant clubmosses and tree ferns, alongside the world's largest-ever insects and the first true reptiles. Marine Carboniferous sites include the iconic Mazon Creek lagerstätte and the limestone coral reefs of the British Mid- and Upper-Carboniferous.

A cast of Lepidodendron bark, its surface covered in the diamond pattern left by fallen leaves
Photo: Daderot, CC0, via Wikimedia Commons

The Carboniferous split into two worlds. Warm shallow seas laid down thick limestone across what is now Britain and the American Midwest. Vast coastal swamps grew the forests that later became coal. Oxygen levels rose higher than at any other time in Earth history, and arthropods reached sizes never repeated since.

Which fossils you find depends on which of those worlds you stand in. Limestone yields crinoids, brachiopods, corals, and bryozoans. Crinoid stems break into small discs that litter some bedding planes. Coal measure shales instead yield plants. Lepidodendron bark carries a diamond pattern of leaf scars, and ferns preserve as dark films on grey shale.

Of the eighteen Carboniferous entries here, thirteen allow free collecting. That is the highest proportion of any period covered. Six sit in the United Kingdom. Joggins in Nova Scotia stands apart from the rest of them. There the Bay of Fundy tides erode fossil trees still standing in growth position, exactly where they grew.

18 fossil sites

Updated 4 August 2026

Life of the period

Three to know from the Carboniferous

You will not find all of these yourself. They are the animals and plants that make the period worth reading about.

  • A life-size model of a giant millipede crossing damp sand.
    Giant millipedeArthropleura

    The largest land arthropod known, with estimates around 2.5 metres. It left trackways as wide as a footpath. High oxygen levels in Carboniferous air allowed arthropods to reach sizes impossible today.

    Prehistorica CM, CC BY 4.0

  • A reconstruction of a giant dragonfly in flight above water.
    Giant dragonflyMeganeura

    A wingspan near 70 centimetres, comparable to a large gull. Insects breathe through tubes rather than lungs, and that system only scales up in oxygen-rich air, which the Carboniferous had.

    Michael Barera, CC BY-SA 4.0

  • A diorama of a Carboniferous forest floor with the scaly base of a lycopsid trunk.
    Scale treeLepidodendron

    Grew over 30 metres in a few years, reproduced once, then died. It was closer to a giant clubmoss than to any modern tree. Its bark carries the diamond leaf scars you find in coal measure shale.

    James St. John, CC BY 2.0

All Carboniferous sites

Frequently asked questions

What is the difference between coal measure and limestone fossils?
Coal measures formed in freshwater swamps and yield plants, with occasional insects and amphibians. Limestone formed in clear marine water and yields crinoids, brachiopods, and corals. The two assemblages rarely occur in the same bed.
How do I identify a Lepidodendron?
Look for a regular diamond pattern across the surface of a bark cast. Each diamond is a leaf scar. The pattern spirals around the trunk and looks like nothing on a modern tree.
What are the small discs in Carboniferous limestone?
Crinoid ossicles, the stacked segments of a crinoid stem. Each disc has a central hole and often a star-shaped or fluted outline. Complete crowns are rare because the stems fell apart soon after death.