Systematic Paleontology Class: Cephalopoda Subclass: Ammonoidea Order: Ammonitida Family: Acanthoceratidae Subfamily: Acanthoceratinae Genus: Acanthoceras Acanthoceras is the type genus for the Ammonitida family Acanthoceratidae which lived during the Cenomanian stage of the Cretaceous period. The shell is evolute, all whorls exposed. Ribbing is strong, tubercles distinct. The whorl section may be round or squarish. Romaniceras, also assigned to the Acanthoceratinae, is similar in overall form.