The Cyrtogomphoceratidae is a family in the cephalopod order 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...

 that comprises genera commonly with compressed, endogastrically curved shells. Siphuncles lie close to the venral side, segments are broadly inflated, connecting rings thick and apically expanded thick bullettes. Chambers are short, separated by shallow, dish shaped septa. Apertures are generally simple.

The Cyrtogomphoceratidae are derived from the discosorid family Reudemannoceratidae

Reudemannoceratidae

The Reudemannoceratidae are the ancestral and most primitive of the Discosorida, an order of cephalopods from the early Paleozoic. The Reudemannoceratidae produced generally medium sized endogastric and almost straight shells with the siphuncle slightly ventral from the center.-Derivation:The...

, probably from Reudemannoceras, through the ancestral genus Ulrichoceras

Ulrichoceras

Ulrichoceras is recognised as the basal cyrtogomphoceratid genus, which is the source for the rest of the Cyrtogomphoceratidae as well as for the Westonoceratidae...

, and have a range from the Middle Ordovician to the Lower Silurian.

The family includes the following genera.

• Cyrtogomphoceras
• Kiaeroceras
• Konglungenoceras
• Landeroceras
  Landeroceras
  Landeroceras is a straight shelled cyrtogomphoceratid from the Middle Ordovician Big Horn dolomite of Wyoming.The shell of Landeroceras is a subcylindrical brevicone with the siphuncle on one side, determined as ventral. Siphuncle segments are short and well expanded into the chambers...
  
  
• Parryoceras
• Strandoceras
  Strandoceras
  Strandoceras is a stronly curved cyrtogomphoceratid with a laterally compressed cross section from the middle and upper Ordovician of Northern Europe; Estonia, Norway, the U.K....
  
  
• Ulrichoceras
  Ulrichoceras
  Ulrichoceras is recognised as the basal cyrtogomphoceratid genus, which is the source for the rest of the Cyrtogomphoceratidae as well as for the Westonoceratidae...
  
  

Ulrichoceras is also considered the source for the exogastric Westooceratidae. The Cyrtogomphoceratidae, through Strandoceras

Strandoceras

Strandoceras is a stronly curved cyrtogomphoceratid with a laterally compressed cross section from the middle and upper Ordovician of Northern Europe; Estonia, Norway, the U.K....

, gave rise to the Silurian - L Devonian Phragmoceratidae

Phragmoceratidae

The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian...

which differ primarily in having thin connecting rings and variably modified, strongly contracted apertures.

References

• Flower, R H and Teichert, C; 1957. The Cephalopod Order Discosorida. University of Kansas Paleontological Contributions. Mollusca, Article 6, pp 1-144.
• Teicher, C. 1964. Nautiloidea-Discosorida. Treatise on Invertebrate Paleontology, Part K. Teichert and Moore, eds.