Basslerocerida is an order of

nautiloid 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 ...

cephalopods from 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 ...

comprising exogastric longiconic cyrtocones,R. H. Flower and B. Kummel. 1950. A Classification of the Nautiloidea. Journal of Paleontology 24(5):604-616 that is no longer in common use.

Taxonomy

The Order Basslerocerida was established by Flower and Kummel (1950) for forms intermediary between the ancestral

Ellesmerocerida The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that ...

and the more advanced

Tarphycerida The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some, such as ''Aphetoceras'' and ''Estonioceras'', are loosely coiled and gyroconic; ...

and

Oncocerida The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are t ...

. The order, as originally defined, contains two families, the Bassleroceratidae with thick-walled siphuncles which gave rise to the Tarphycerida, and the Graciloceratidae, derived from the former, with thin-walled siphuncles which gave rise to the Onocerida. The speculation in Flower and Kummel (1950) that the Basslerocerida, through the Graciloceratidae, might have given rise to the Barrandeocerida may account for the inclusion of the Barradeocerina in the Basslerocerida in some classifications and the extension of the order to the Devonian. The derivation of barrandeoceroids from within the Tarphycerida is however well established. Basslerocerida has fallen into general disuse, the taxa now being included in either the Ellesmerocerida or in the derived Tarphycerida and Oncocerida, although Sheverev (2006) continued to recognize the order. Furnish and Glenister (1964)Furnish W.M and Glenister, Brian F 1964, Nautiloidea -Ellesmerocerida.

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 ...

, Geol Soc of America and Univ Kansas Press (Teichert & Moore, Eds) included the Bassleroceratidae in the Ellesmerocerida while Sweet (1964)Sweet, Walter C. 1964 Nautiloidea- Oncocerida. Treatise on Invertebrate Paleontology, Geol Soc of America and Univ Kansas Press (Teichert & Moore, Eds) included its derivative, the Graciloceratidae, in the Oncocerida. Flower (e.g. 1976)Flower, R. H. 1976. Ordovician Cephalopod Faunas and Their Role in Correlation, in Bassett, M.C. (Ed); The Ordovician System: Proceedings of a Paleontological Association Symposium; Birmingham, Eng. 1974; Univ of Wales and Welsh Nat’l Mus Press instead included the Bassleroceritidae in the Tarphycerida.

Morphology

Nothing is known about the basslerocerid soft part anatomy, although they may be surmised to have had somewhat squid-like bodies with perhaps 8 or 10 arms. Shells are rather small, reaching lengths of about 12 –15 cm (5 –6 in); elongate with an upward, exogastric, curvature -like a rocker -and subcircular to laterally compressed cross section. The venter on the outer curvature is commonly more sharply rounded, giving it a keel-like form, than the dorsum on the inner curvature. Septa are close spaced, the siphuncle ventral. The siphuncle in the Bassleroceratidae is composed of thick connecting rings as found in the ancestral Ellesmerocerida and in primitive Tarphycerida. Connecting rings in the derived Graciloceratidae are thin, as found in the Oncocerida.

References

Basslerocerida, Paleobiology DB
{{Taxonbar, from=Q4868172 Nautiloids Mollusc orders Ordovician cephalopods Prehistoric cephalopods of North America Prehistoric animals of Europe Prehistoric animals of Asia Obsolete animal taxa