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

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 w ...

, from the

Angara River The Angara ( Buryat and mn, Ангар, ''Angar'', "Cleft"; russian: Ангара́, ''Angará'') is a major river in Siberia, which traces a course through Russia's Irkutsk Oblast and Krasnoyarsk Krai. It drains out of Lake Baikal and is ...

basin in central Russia, named by Balashov in 1962. Its age, as given in the

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') 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 co ...

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 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, exi ...

or the

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 slend ...

References

*Flower, R.H. 1976. Some Whiterock and Chazy Endoceroids. Part II, Mem.28; New Mexico Bureau of Mines and Mineral Resources, 1976. *Teichert, C, 1964. Endoceratoidea. Treatise on Invertebrate Paleontology, Part K. Teichert & Moore, (eds). Geological Society of America and Univ. Kansas Press. {{Taxonbar, from=Q4848895 Nautiloids