Bathmoceras
Encyclopedia
Bathmoceras is a genus of the Ellesmerocerida
, placed in the family Bathmoceratidae, in which Furnish and Glenister 1964 also include Eothinceras. Flower 1964 separates the two genera into their respective families which he included in his suborder, Cyrtocerinina
The shells of Bathmoceras are rather large, straight or faintly exogastric. Sutures are simple except for a sharp mid ventral saddle. The siphuncle
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.
Bathmoceras is of Middle and Late Ordovician
age and has been found in northern and central Europe and in the Macdonnell Ranges
in central Australia.
At one time (Flower 1957) 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. (Flower 1976)
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.
Ellesmerocerida
The Ellesmerocerida is a order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician.-Morphology:...
, placed in the family Bathmoceratidae, in which Furnish and Glenister 1964 also include Eothinceras. Flower 1964 separates the two genera into their respective families which he included in his suborder, Cyrtocerinina
The shells of Bathmoceras are rather large, straight or faintly exogastric. Sutures are simple except for a sharp mid ventral saddle. The siphuncle
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
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.
Bathmoceras is of Middle and Late Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
age and has been found in northern and central Europe and in the Macdonnell Ranges
MacDonnell Ranges
The MacDonnell Ranges of the Northern Territory, are a long series of mountain ranges located in the centre of Australia , and consist of parallel ridges running to the east and west of Alice Springs...
in central Australia.
At one time (Flower 1957) 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. (Flower 1976)
Derivation
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, as indicated in Flower (1964). Eothinoceras differs in that the septal necks are vestigial (Flower 1964) 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 apparetly more slender (Flower 1964).Preservation and cccurrence
Bathmoceras is found in Europe and Australia, mostly as internal molds in sandy sediments (Flower 1964). 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.