Pohlsepia mazonensis is the earliest described octopod, dated at approximately 296 million years old. The species is known from a single exceptionally preserved fossil discovered in the Pennsylvanian Francis Creek Shale of the Carbondale Formation, north-east Illinois, United States. Pohlsepia mazonensis is named after its discoverer, James Pohl, and the type locality, Mazon Creek. Its habitat was the shallows seawards of a major river delta in what at that time was an inland ocean between the Midwest and the Appalachians.