Discosorus , a genus of the Discosorida

Discosorida

Discosorida is a unique order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the chambers in cephalopods, which unlike...

 and member of the family Discosoratidae. Not to be confused with Discoceras

Discoceras

Discoceras, a member of the Trocholitidae in the Tarphycerida, not to be confused with Discosorus.Discoceras is characterized by closely coiled, gradually expanding shells with a subquadrate cross section, that may be ribbed or smooth. The sides are broadly rounded; the venter wide and slightly...

. Discosorus consists of rapidly expanding endogastric brevicones, mostly known from isolated 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...

s composed of broadly expanded segments that increase rapidly in size. Septal necks are recumbent, connecting rings thin, bullettes small. The siphuncle interior is occupied by endocones produced by layered annular deposits expanded back toward the apex, leaving a central tube running down the middle. The short phragmocone is poorly known.

Discosorus is found in the Middle Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 of eastern and arctic North America and as part of the Discosoratidae is derived from the Lowoceratidae

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...

 which forms a link in the Early Silurian from the 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...

 exogastric Faberoceras

Faberoceras

Faberoceras is an extinct genus of prehistoric nautiloid. The nautiloids are a subclass of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species.-References:...

of the Westonoceratidae

Westonoceratidae

Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian.The siphuncle is typically close to the convexly curved outer margin of the phragmocone -the chambered part of the shell- taken to be ventral but may be more central in...

.