Earliest known octopus
Pohlsepia mazonensis
First first
United States ()

The earliest known octopus is Pohlsepia mazonensis, dating back some 296 million years to the Carboniferous Period. Its only known fossil was found in northeastern Illinois, USA, and has been variously described as resembling a flattened cow pat or a globular splat, but it possesses eight tentacles, two eyes, and what may be an ink sac – all features characterizing octopuses of today. It was formally described and named in 2000, and its sole pecimen is housed in Chicago's Field Museum of Natural History.

Pohlsepia mazonensis is named after its discoverer, James Pohl, who donated it to the Field Museum; and its provenance, Mazon Creek, which is a major fossil locality close to Morris in Grundy County, Illinois.

It lived in what were then the shallows seaward of a major river delta.