• Soft part preservation;
  • cephalopod;
  • Mazon Creek fossils;
  • Upper Carboniferous;
  • Francis Creek Shale;
  • Illinois;
  • USA

A ten armed fossil from the Pennsylvanian Francis Creek Shale and belonging to the famous Mazon Creek biota is described as a cephalopod. Apart from a superficial resemblance to the coleoids, there is little basis for an assessment of the animal's affinities. A mineralized Bask shaped structure preserved in calcite and seen in both part and counterpart in fragmentary form may represent the fossilized remains of an internal organ such as the stomach or ink sac A small, dark circular spot positioned anterior to the appendages could be the animal's eye although mere is no internal structure visible. The extremely rare occurrence of Palaeozoic cephalopods with soft parts has so far been Ended to the Francis Creek Shale and the Devonian Hunsrückschiefer of Germany. The Mazon Creek biota includes many fossils which show a remarkable standard of soft part preservation which in some cases includes the fossilization of eye spots and stomach traces. Previously deserted Mazon Creek cephalopods have included the tentacular impression of a squid complete with arm hooks, and the radulae and shells of both coleoids and nautiloids. The specimen described here is the first from the Palaeozoic to show any hint of organ preservation.