''Beekmanoceras'' is a small

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

from the Middle

Canadian Epoch The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century. However it has no official recognition by the International Commission on Stratigraphy ( ...

of New York with a loosely coiled, gyroconic, shell in which the whorls are not in contact and the

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 ...

is on the inner or concave side of the whorl. Furnish and Glenister (1964) placed ''Beekmanoceras'' in the Trocholitidae (

Tarphycerida The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some, such as '' Aphetoceras'' and '' Estonioceras'', are loosely coiled and gyroconi ...

), interpreting the curvature to be ventral side convex, i.e. exogastastric and the

to be dorsal.

Flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

(1964) included ''Beekmanoceras'' in the

Ellesmeroceratidae The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the do ...

believing the siphuncle to be ventral and the curvature to be endogastric with the ventral side concave. Structural details of the

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

''Beekmanoceras priscum'' the only species known, are obscure, allowing for different interpretations (ibid). A few things can be said however. No other trocholitids are known to have an openly coiled gyroconic shell which casts doubt on that placement. On the other hand, no endogastric forms are known for sure to have developed the kind of gyroconic coiling found in ''Beekmanoceras''.

References

* Flower, Rousseau H, 1964; The Nautiloid Order Ellesmeroceratida (Cephalopoda); New Mexico Bureau of Mines and Mineral Resources, Mem 12, p. 96 *Furnish, W.M & Glenister, Brian F.; Nautiloidea—Tarphycerida, in the ''

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

'', Vol K, Teichert and Moore Eds, Pub GSA and Univ Kansas; p. K360. {{Taxonbar, from=Q4879836 Nautiloids