Orthoceras choctawense
Nautiloid
Upper Mississippian (Middle Chesterian)
Delaware Creek Member, Caney Shale Formation
Clarita, Coal County, Oklahoma, USA

85mm orthocerid with 16mm Goniatites choctawensis on 135mm matrix.

Cephalopod. Ammonite. Association.

Orthoceras is a genus of straight-shelled nautiloid with a long chronologic range (Ordovician to Triassic) and a wide paleogeographic range (North America, Europe, China, North Africa, Madagascar, Indonesia).

Orthoceras is perhaps best-known from the huge number of polished specimens sold to tourists and casual collectors at mineral shows and flea markets.  It’s true they are actual nautiloid specimens but researchers have determined that at least most of those specimens actually belong to the genus, Geisonoceras.

Unusual matrix piece with a nautiloid and an ammonite.