Acompsoceras

Acompsoceras is a genus of cephalopod belonging to the Ammonite subclass. It grew to a large size compared to most ammonites. Its shell reached 18 inches (46 cm) in diameter when the animal reached adulthood. Acompsocerasappears in the fossil record during the early portion of the Cretaceous Cenomanian stage and goes extinct around the middle of that same stage.