''Megadisocosorus'' is a genus of

actinocerid The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposit ...

cephalopods similar to ''

Armenoceras ''Armenoceras'' is a genus of actinocerida, actinocerid nautiloid cephalopods whose fossils ranged from the late Whiterockian Stage in the early Middle Ordovician, through the remainder of the period and on into the Upper Silurian. It is the typ ...

'' but with a short, slightly curved, breviconic shell. The siphuncle is in contact with the ventral wall, unlike that of ''Armenoceras'' in which the siphuncle is close to the center. ''Megadisocosorus'' is known from the Middle

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

of North America. According to Teichert, 1964, ''Megadisocosorus'' is a member of one of the two branches of the

Armenoceratidae The Armenoceratidae are a family of early Paleozoic nautiloid cephalopods belonging to the order Actinocerida.Flower 1957.Studies of the Actinoceratida.; Memoir 2; New Mexico Bureau of Mines and Mineral Resources, Socorro, NM Teichert 1964. Act ...

that also includes ''

Nybyoceras ''Nybyoceras'' is an actinocerid genus assigned to the Armenoceratidae and similar to ''Armenoceras'' except for having a siphuncle close to the ventral side of the shell. Morphology As with ''Armenoceras'', ''Nybyoceras'' has a medium to large ...

'' and ''

Selkirkoceras ''Selkirkoceras'' is a genus of armonoceratid cephalopods similar to ''Kochoceras'' of the Actinoceratidae, but with recumbent septal necks. The first siphuncular segment is large, broad, and blunt. ''Selkirkoceras'', which is known from the Mid ...

''.

References

* Curt Teichert, 1964. Actinoceratoidea,

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

, Part K. Geological Society of America and University of Kansas Press. Prehistoric nautiloid genera Actinocerida {{paleo-nautiloidea-stub