Bajkaloceras is a straight-shelled orthoceroid, and possibly a member of the Intejocerida

Intejocerida

Intejocerida is the name given to a group of generally straight shelled nautiloid cephalopods originally found in Lower and Middle Ordovician sediments in the Angara River basin in Russia; defined in the Treatise as an order, and combined there with the Endocerida in the...

, from the Angara River

Angara River

The Angara River is a long river in Irkutsk Oblast and Krasnoyarsk Krai, south-east Siberia, Russia. It is the only river flowing out of Lake Baikal, and is the headwater tributary of the Yenisei River....

 basin in central Russia, named by Balashov in 1962. Its age, as given in the Treatise on Invertebrate Paleontology

Treatise on Invertebrate Paleontology

The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...

 is Arenigian.

Description

Bajkaloceras is characterized by an orthonic shell with an elliptical cross section and short camerae and a large, central to subctral siphuncle composed of moderately concave segments with short septal necks and apparently thin connecting rings. In the early growth stage, the interior of the siphuncle, is lined with calcareous deposits that seem to be outgrowths of the connecting rings, which are divided into numerous cells by longitudinal and transverse partitions.

Taxonomic position

Bajkaloceras is the sole member and representative of the Bajkaloceratidae, proposed by Balashov, 1962, and given ordinal rank by Sheveyrev, 2006. Teichert (1964), in the Treatise, Pt K, included Bajkaloceras, and Bajkaloceratidae, along with Intejoceras, Evencoceras, and Padunoceras in the Intejocerida which he joined with the Endocerida in the Endoceratoidea. Flower (1976) separated these into two groups, calling attention to differences in siphuncle morphology and location. Thin connecting rings and the central or subcentral siphuncle separate Bajkaloceras form the endoceroids and suggest a close relationship with the 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...

 or the Troedssonellidae

Troedssonellidae

Troedssonellidae is a family of orthoceroid cephalopods from the Ordovician, derived from rod-bearing Baltoceratidae, that have a continuous lining within the siphuncle that resembles very thin and slender endocones. Shells are generally slender and orthoconic. The siphuncle is central or...