''Bathmoceras'' is a primitive

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

genus from the Middle and Upper Ordovician. It is a member of the order

Cyrtocerinida Cyrtocerinida is an order of Ordovician nautiloid cephalopods. The order includes the families Cyrtocerinidae and Eothinoceratidae, as well as the genera '' Bathmoceras'' and '' Rummoceras''. Cyrtocerinids can be characterized by a broad siphu ...

and is the only genus in the family Bathmoceratidae.

Derivation

At one time ''Bathmoceras'' was thought to have possibly given rise to ''Polydesmia'', once thought to have been the ancestral actinocerid. Since then revision of actinocerid phylogeny and of Ordovician stratigraphy in east Asia have cast doubts on this hypothesis. ''Bathmoceras'' is most likely derived from ''Eothinoceras'' through lengthening of the septal necks and of the inward projections of the connecting rings in a forward direction. ''Eothinoceras'' differs in that the septal necks are vestigial rather than being somewhat long as in ''Bathmoceras'' and that the inward projections of the connecting rings point straight in rather than projecting forward. Both are straight shelled or slightly exogastric. Eothinoceras is also apparently more slender. Furnish and Glenister also included '' Eothinceras'' in the family

Bathmoceratidae ''Bathmoceras'' is a primitive cephalopod genus from the Middle and Upper Ordovician. It is a member of the order Cyrtocerinida and is the only genus in the family Bathmoceratidae. Derivation At one time ''Bathmoceras'' was thought to have pos ...

. R.H. Flower, 1964, separates the two genera into their respective families within the ellesmerocerid suborder Cyrtocerinina, now known as the order Cyrtocerinida.

Preservation and occurrence

''Bathmoceras'' is of Middle and Late

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

age and has been found in northern and central Europe and in the

Macdonnell Ranges The MacDonnell Ranges, or Tjoritja in Arrernte language, Arrernte, is a mountain range located in southern Northern Territory. MacDonnell Ranges is also the name given to an Interim Biogeographic Regionalisation for Australia, interim Australia ...

in central Australia. The genus is found in Europe and Australia, mostly as internal molds in sandy sediments. One species ''B. linnarsoni'' was found in limestone in Sweden which allowed Holms to conduct thin section studies.

Paleoecology and lifestyle

The common occurrence in sandy sediments indicates that ''Bathmoceras'' lived over sandy bottom, although some species obviously did spend time over carbonate shelves. The straight or slightly upwardly curved, exogastric shells with weighted ventral siphuncles indicate a normal horizontal orientation with the aperture facing forward. They were apparently active predators with some degree of mobility. As for the peculiar internal structure of the siphuncle, beyond providing ballast, no reason has been given.

Description

The shells of ''Bathmoceras'' are rather large, straight or faintly exogastric. Sutures are simple except for a sharp mid ventral saddle. The

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

is large and near the venter, in which the segments have a slightly sinuous outline. Septal necks are rather long. Most diagnostically, the connecting rings are thickened into forward projecting lobes that may extend internally two or three segments within the siphuncle.

References

{{Taxonbar, from=Q4869043 Ellesmerocerida Ordovician cephalopods Ordovician cephalopods of Europe Middle Ordovician first appearances Late Ordovician extinctions