Discosoridae comprise a family of endogastric discosorids, (Cephalopoda, Nautiloidea), with endocones in the siphuncle, ranging from the Middle Silurian to Middle Devonian.

Shell morphology

The shell in the Discosoridae is conical, expanding variably with respect to genus. Curvature tends to be slight with the ventral or siphuncular side slightly concave in profile (the endogastric condition), and the opposite dorsal side arched or convex in profile (another endogastric condition). 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 composed of broadly rounded segments the increase rapidly in size toward the aperture, with growth. Expansion is commonly greater than that of the shell itself, and lies ventral of the center. Septal necks are short, brims long and recumbent. Connecting rings are thin and poorly known. Bullettes at the apical end of the connecting rings, which grasp the periphery of the previous septal foramina and connect to the inside of the previous septal necks, are never swollen. Endocones are formed by overlapping parietal deposits that line in inner side of the siphuncle in the apical part of the shell. The internal contour is wavy, in contrast to the straight conical contours of the endocerid endocones, following the general configuration of the siphuncle. The narrow endosiphotube, left within the adapical portion, may contain diaphragms. Complete shells are rare. Most of the information regarding comes from isolated siphuncles

Origin

The Discosoridae are thought to be derived from the

Lowoceratidae The Lowoceratidae is a small family of discosorids, early nautiloid cephalopods, from the Middle Silurian in which the characteristic bullette is found only in early growth stages. Lowoceratids were first found in Southampton Island in the Ca ...

, a small family of variably exograstric discosorids, probably from ''Lowoceras'' the straighter of the two.

Genera

Genera belonging to the Discosoridae include: :''

Discosorus ''Discosorus'', a genus of the Discosorida and member of the family Discosoridae. Not to be confused with ''Discoceras''. ''Discosorus'' consists of rapidly expanding endogastric brevicones, mostly known from isolated siphuncles composed of broad ...

'', type :'' Alpeboceras'' :'' Endodiscosorus'' :''

Kayoceras ''Kayoceras'' is a genus of middle Silurian nautiloid cephalopods, known from Iowa and Illinois, belonging to the Discosoridae. Related genera include ''Discosorus'', '' Endodiscosorus'', and '' Stokesoceras''. ''Kayoceras'' has a short, brevicon ...

'' :'' Stokesovers'' : and possibly ''

Konglungenoceras ''Konglungenoceras'' is a discorid from the lower Silurian of Europe (Norway) included in the Cyrtogomphoceratidae that lacks the septal foramina grasping bullettes at the adapical end of the connecting rings. shells are endogastric and strongly ...

'' unless

Cyrtogomphoceratidae The Cyrtogomphoceratidae are a family in the cephalopod order Discosorida that comprises genera commonly with compressed, endogastrically curved shells. Siphuncles lie close to the ventral side, segments are broadly inflated, connecting rings th ...

References

* Flower, R.H.and Curt Teichert 1957. The Cephalopod Order Discosorida. University of Kansas Paleontological Contributions, Mollusca, Article 6. July 1957 * Teichert, C 1964. Nautiloidea -Discosorida. Treatise on Invertebrate Paleontology Part K. Geological Soc of America and Univ. Kansas Press {{Taxonbar, from=Q16981386 Discosorida Silurian animals Devonian animals Silurian first appearances Middle Devonian extinctions Prehistoric nautiloid families