Cameroceras

Cameroceras ("chambered horn") is a genus of extinct, giant orthoconic cephalopod that lived mainly during the Ordovician period. It first appears during the middle Ordovician, around 470 million years ago, and was a fairly common component of the fauna in some places during the period, inhabiting the shallow seas of Laurentia, Baltica and Siberia.[1]  Its diversity and abundance became severely reduced following the Ordovician–Silurian extinction events, and the last remnants of the genus went extinct sometime during the Wenlock.[1]