The Montceau-les-Mines Lagerstätte (Late Carboniferous, France)

The Montceau-les-Mines Lagerstätte (Late Stephanian, Late Carboniferous) is located northeast of the French Massif Central. Situated at equatorial latitudes during the Pennsylvanian, this Lagerstätte, probably a freshwater environment, preserves a rich and diverse flora (lycopsids, sphenopsids, ferns, pteridosperms, and cordaites) and fauna (bivalves, annelids, crustaceans, myriapods, insects, chelicerates, myxinoids, actinopterygians, sarcopterygians and tetrapods). These exceptionally preserved fossils can be found either flattened in shales or three-dimensionally preserved in sideritic nodules. The fossils from the nodules are exceptional for at least two reasons: the absence of major disarticulation of their body structure and the preservation of soft parts and extremely fragile cuticular structures. Such preservation was made possible by the combination of several factors: rapid burial in fine anoxic mud, early siderite precipitation (inducing the nodule formation) and phosphatization of cuticles and soft-bodied features.