Acompsoceras is an extinct genus of cephalopod belonging to the Ammonite

Ammonite

Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

 subclass. It grew to a large size compared to most ammonites. Its shell reached 18 inches (45.7 cm) in diameter when the animal reached adulthood. Acompsoceras appears in the fossil record during the early portion of the Cretaceous Cenomanian

Cenomanian

The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...

 stage and goes extinct around the middle of that same stage.

Classification

Acompsoceras is in the same family as Acanthoceras, the Acanthoceratidae

Acanthoceratidae

Acanthoceratidae is an extinct family of cephalopods belonging to the Ammonite subclass. The Type genus is Acanthoceras.-Referenceas:*http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=95294&is_real_user=1...