Troedssonellidae is a family of orthoceroid

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

 cephalopods from the 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...

, derived from rod-bearing Baltoceratidae

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, existing for approximately .-Taxonomy:Baltoceratidae was...

, that have a continuous lining within the 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...

 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.

Troedsonnellids first appear high in Lower Ordovician (Cassinian

Cassinian

The Cassinian is the latest age of the Canadian Epoch when thought of temporally and the uppermost stage of the Canadian Series when thought of stratigraphically...

) strata, beginning with Tajaroceras

Tajaroceras

Tejaroceras is an extinct slender cephalopod from the uppermost Lower Ordovician of western North America, belonging to the Orthocerid family Troedssonellidae....

and extend at least through the Whiterock Stage

Whiterock Stage

The Whiterockian, often referred to simply as the Whiterock, is a earliest or lowermost stage of the Middle Ordovician.. Although the Whiterockian or Whiterock Stage refers mainly to the early Middle Ordovician in North America, it is often used in the older literature in a global sense.The...

 of the Middle Ordovician. They also may have given rise to the Striatoceratidae and to the Narthecoceratidae

Narthecoceratidae

Narthecoceratidae is an extinct genus of actively mobile carnivorous cephalapod, essentially a Nautiloid, that lived in what would be North America during the Ordovician from 460.5—449 mya, existing for approximately .-Taxonomy:...

of the Middle and Late Ordovician.

Gerera include Tajaroceras, Buttsoceras, Oxfordoceras, Ctenoceras, Troedsonnella and the possible Glenisteroceras and Wolungoceras