Cameroceras ("chambered horn") was a genus of giant orthocone cephalopod that lived in the Ordovician period.
The partial shell of one giant Cameroceras yielded a total length estimated at the time at nearly 30 feet (9 m). (This estimate has since been revised downward quite a bit.) Regardless of this estimate's degree of accuracy, this gargantuan cephalopod was one of the largest animals ever to live during the Paleozoic Era, if not the largest. Judging from its huge size, it was likely an apex predator that lived in deeper water (it would possibly have been unable to maneuver in shallow water), and probably fed on eurypterids such as Megalograptus, large trilobites, and smaller cephalopods.