Troedssonellidae is a family of orthoceroid cephalopods from the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

, derived from rod-bearing

Baltoceratidae Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, exist ...

, that have a continuous lining within the

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

that resembles very thin and slender endocones. Shells are generally slender and orthoconic. The siphuncle is central or subcentral, composed of straight or slightly expanded segments. Septal necks generally short and connecting rings are thin. Thin cameral deposits (lining the chambers) are known, which along with the position of the siphuncle and thin connecting rings distinguishes them from the endocerids in which they have been included.Flower 1976. Ordovician Cephalopod Faunas and Their Role in Correlation, in The Ordovician System: proceedings of a Palaeontological Association symposium, Sept 1974 Troedsonnellids first appear high in Lower Ordovician ( Cassinian) strata, beginning with ''

Tajaroceras ''Tajaroceras'' is an extinct slender cephalopod from the uppermost Lower Ordovician of western North America, belonging to the Orthocerid family Troedssonellidae. Background The shell of ''Tajaroceras'' is smooth and straight. The siphuncle w ...

'' and extend at least through the Whiterock Stage of the Middle Ordovician.Hook and Flower 1977. Late Canadian (Zones J,K) Cephalopod Faunas from Southwestern United States: Memoir 32, New Mexico Bureau of Mines and Mineral Resources. They also may have given rise to the Striatoceratidae and to the Narthecoceratidae of the Middle and Late Ordovician.

Genera

*''

'' *'' Buttsoceras'' *'' Oxfordoceras'' *'' Ctenoceras'' *'' Troedsonnella'' Genera of dubious placement: *'' Glenisteroceras'' *'' Wolungoceras''

References

{{Taxonbar, from=Q7844939 Orthoceratoidea