Cameroceras, fromAncient Greek καμάρα (kamára), meaning "chamber", and κέρας (kéras), meaning "horn", is anextinct genus ofendoceridcephalopod which lived in equatorial oceans during the entireOrdovician period. Like other endocerids, it was anorthocone, meaning that its shell was fairly straight and pointed. It was particularly abundant and widespread in the Late Ordovician, inhabiting the shallow tropical seas in and aroundLaurentia,Baltica andSiberia (equivalent to modern North America, Europe, and Asia).^[1]

Cameroceras Temporal range:Ordovician PreꞒ Ꞓ O S D C P T J K Pg N
Partial internal mold ofC. inaequabile, Upper Ordovician of northern Kentucky
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	†Endocerida
Family:	†Endoceratidae
Genus:	†Cameroceras Conrad, 1842
Type species
†Cameroceras trentonense Conrad, 1842
Species
See text.

Cameroceras exhibited a broad range of sizes, and some species were fairly large by extinct cephalopod standards. One species,C. turrisoides from theBoda Limestone ofSweden,^[2] is estimated to have shell around 2 metres (6.6 ft) in length,^[3] while that ofC. rowenaense was about 70 centimetres (2.3 ft).^[1] Some books and older scientific papers previously treatedCameroceras as the absolute largestnautiloid-grade cephalopod, with a shell length reaching 5.7 metres (19 ft)^[4][5] or even 9.14 metres (30.0 ft).^[6][4][1] More recent studies have indicated that the largest orthocone fossils do not belong to the genusCameroceras, but ratherEndoceras giganteum. Moreover, the maximum length estimate is based on a highly doubtful field observation.^[5]Cameroceras andEndoceras are indistinguishable in most anatomical aspects, only differing in their shell texture.^[7]

Cameroceras is acephalopod, the same group of molluscs that includes the octopuses, squids and cuttlefish. The only portion of the animal to fossilize is the shell (formally known as the conch). Like other orthoconic nautiloids,Cameroceras had a narrow conical shell with smooth, simple sutures dividing a series ofsepta (internal chambers). In cross-section, the shell may be perfectly circular or slightly depressed (elliptical, wider than tall).^[7]

The position of thesiphuncle varies, but in most species it runs close to the lower edge of the shell. In some species the siphuncle is voluminous, reaching a diameter equal to half of the shell diameter. The siphuncle is filled with stacked funnel-shaped concretions known as endocones, which have a simple conical form inCameroceras.^[7] A thin endosiphuncular tube passes through the apex of each endocone, in the lower part of the siphuncle. The surface of the siphuncle is supported byseptal necks which are holochoanitic, meaning that they fully sheath the siphuncle and extend all the way between each septum. The main difference betweenCameroceras andEndoceras is thatCameroceras lacks annulations (thin concentric rings) on the outer surface of the shell.^[7]

From comparison with living cephalopods, particularly the shellednautilus, some inferences about the biology ofCameroceras can be made. The head of the animal would have been soft muscular tissue situated at the opening of the shell, with themantle (sheath-like body wall) lying within the shell for protection. Tentacles would have grown from the base of the head, and these tentacles would have been used to seize and manipulate prey. At the base of these tentacles within the buccal mass (analogous to the mouth) a hard keratinous beak would have bitten into the bodies of its prey, and is assumed to have been strong enough to breach the prey's exoskeleton or shell. Modern cephalopods beaks contain aradula, or 'toothed' tongue, which is used to rasp out soft tissue from within the prey's shell.

Cameroceras has historically been utilized as a "wastebasket taxon" in which species of large orthoconic endocerids such asEndoceras,Vaginoceras, andMeniscoceras were originally placed. This poses difficulty for describingCameroceras as a distinct genus. The type speciesCameroceras trentonense was named by Conrad in 1842, based on fossils from theTrenton Limestone of western New York state.^[8] The original specimen ofC. trentonense is apparently lost, which complicates comparisons to other endocerids.^[6]

Hall, who named and describedEndoceras annulatum in 1847, recognizedC. trentonense as a valid combination, but usedEndoceras for other specimens of large endocerids from the Trenton Limestone. Sardeson (1925/1930) suggested thatCameroceras andEndoceras are potentially different growth stages of the same genus,^[9][10] though other authors have doubted this perspective.^[6]

For many historical studies,Cameroceras was considered to take precedence overEndoceras whenever the two refer to the same species, according to theprinciple of priority.^{[11][9][10][1]}Cameroceras' vague early descriptions have led other authors to preferEndoceras or other better-described genera when the nomenclature is in question.^[6] Recent studies generally accept bothCameroceras andEndoceras as valid genera, even some species are in an unstable state between the two.^{[7][2][3][12]}

Fossils assigned toCameroceras have been found in North America, Asia, and Europe throughout the Ordovician, though most species occur in theKatian stage of the Late Ordovician. Reports ofCameroceras fossils from theWenlock epoch of the Silurian are based onRossicoceras hudsonicum,^[13] anOntarian endocerid species sometimes placed withinCameroceras.^[7] Species which are currently referred toCameroceras rather than to other endocerids include:

• Cephalopod size

• Sweet, Walter C. Cephalopoda—General Features inTreatise on Invertebrate Paleontology, Part K, Mollusca 3. Geological Society of America, and University of Kansas Press. Page K5.