DescriptionOrthocerasBW.jpg English: Orthoceras sp., nautiloid from the middle Ordovician. Digital. Date 24 March 2009 Source Own work Author Nobu Tamura
domain) Geisonoceratidae: File:Orthoceras_BW.jpg - by Nobu Tamura (CC BY 3.0) Pachycormidae: File:Leedsichthys_new1DB.jpg - by Dmitry Bogdanov (CC BY 3
