Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass

Nautiloidea Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded specie ...

endemic to what would be

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

, Australia,

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

, North America, and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

during the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

living from about 480–460 mya, existing for approximately .

Taxonomy

Baltoceratidae was named by Kobayashi (1935) and assigned to the Ellesmeroceratida by Flower and Kummel (1950) where it was retained by Unklesbay and Young (1956), again by Flower (1964)Flower 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda), Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM , and by Furnish and Glenister in Teichert et al. (1964).Teichert et al 1964,

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 ...

Part K Mollusca 3, Nautiloidea-Ellesmerocerida by Furnish and Glenister, K129- K153 Flower (1964) included the Baltoceratidae in the ellesmeroceratid suborder Ellesmeroceratina. Further study of baltoceratid interiors, namely regarding the generally thin connecting rings and lack of siphuncular diaphragms, showed they are distinct from the typical ellesmerocerids and belong, as the ancestral group, to the Orthocerida where assigned by Kroger et al. (2007) B. Kröger, M. S. Beresi, and E. Landing. 2007. Early orthoceratoid cephalopods from the Argentine Precordillera (Lower-Middle Ordovician). Journal of Paleontology 81(6):1266-1283

Diagnosis

The Baltorceratidae are characterized by dominantly straight, slender, smooth shells with a moderately large ventral siphuncle composed of orthochoanitic

septal In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatr ...

necks and thin connecting rings, free of diaphragms and which in advanced forms becomes more central in position. Septa are close spaced, resulting in short camerae and may form shallow ventral lobes. Cameral deposits are normal which develop apically and more ventrally. Two stocks are found within the Baltoceratidae, those with a calcareous rod secreted on the lower surface of the inside of the siphuncle known as "rod-bearing" and those without, in which the interior of the siphuncle tube is empty, known as "vacuosiphonate".S.C. Hook & R.H. Flower 1977. Late Canadian (Zones J, K) Cephalopod Faunas from Southwestern United States; Memoir 32, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM Empty siphuncled forms, the vacuosiphonate, gave rise to the Michelinoceratidae, commonly known as the Orthoceratidae, which has its beginning in the lower Cassinian stage in the latter part of the Lower Ordovician. Rod bearing forms gave rise to the Troedsonnellidae with early members, '' Buttsoceras'' and '' Tajaroceras'' found in the upper Cassinian. The Baltoceratidae and Orthoceratidae both have a spherical apex that lacks a cicatrix, and similar, two-layered thin connecting rings which clearly places the Baltoceratidae in the Orthocerida as well. Furthermore, the Baltoceratidae are restricted to forms with a siphuncle that is tubular or slightly expanded within the chambers, excluding genera with a more ellesmeroceratid aspect in which connecting rings thicken inwardly, such as ''Amsleroceras'', '' Cyptendoceras'', and '' Rioceras'' .

References

{{Taxonbar, from=Q4853002 Orthocerida Prehistoric cephalopod families Ordovician cephalopods Prehistoric animals of Asia Prehistoric cephalopods of North America Prehistoric invertebrates of Oceania Prehistoric animals of Europe Paleozoic animals of South America Cephalopods of Asia Molluscs of Oceania Molluscs of Europe Molluscs of North America Cephalopods of South America Ordovician first appearances Middle Ordovician extinctions

Taxonomy

Diagnosis

See also

References