Fine Mazon Creek Acanthodian Fossil Fish Acanthodes

Description: The Mazon Creek deposits of the region near Braidwood, Illinois rival the other famous Lagerstatten of the Burgess Shale, Solnhofen, and Liaoning for the variety of detailed life preserved. Many exquisitely-preserved specimens are found in the ironstone nodules that make up the deposits. The majority of collecting areas are the spoil heaps of abandoned coal mines, the most famous of which is Peabody Coal Pit 11. Pit 11 now serves as a cooling pond for the Braidwood nuclear power plant, but with over 100 other localities, specimens still come to light. This one is of the fossil fish Acanthodes, preserved here in dorsolateral aspect. The Acanthodians are jaw-bearing fish who still are the subject of dispute over their systematic position. They possess highly-advanced, spindle-shaped bodies thought to have made them swift swimmers. The body was covered in small mosaic-like scales. They possessed small teeth which were typically confined to the lower jaw; some were toothless. The feature they all share in common is the fact that all fins other than the caudal are supported by massive spines formed of dentine. Indeed, the name Acanthodii is derived from the Greek word for spine. Note the spibnes preserved here. The oldest acanthodian lived during the late Ordovician. They reached their peak during the Devonian, and became extinct during the Great Dying of the end-Permian extinction..