Basslerocerida

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Basslerocerida
Temporal range: Ordovician
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order:Basslerocerida
Flower & Kummel, 1950

Basslerocerida is an order of nautiloid cephalopods from the Ordovician comprising exogastric longiconic cyrtocones, [1] that is no longer in common use.

The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.

Contents

Taxonomy

The Order Basslerocerida was established by Flower and Kummel (1950) for forms intermediary between the ancestral Ellesmerocerida and the more advanced Tarphycerida and Oncocerida. [1] 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) [1] 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.

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.

The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician to the Middle Devonian. Some, such as Aphetoceras and Estonioceras, are loosely coiled and gyroconic; others, such as Campbelloceras, Tarphyceras, and Trocholites, are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular, as much as half the length of the containing whorl in most, greater than in the Silurian Ophidioceratidae. The Tarphycerida evolved from the elongated, compressed, exogastric Bassleroceratidae, probably Bassleroceras, around the end of the Gasconadian through forms like Aphetoceras. Close coiling developed rather quickly, and both gyroconic and evolute forms are found in the early middle Canadian.

Oncocerida order of molluscs

The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian, in which the connecting rings are thin and siphuncle segments are variably expanded. At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three.

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) [2] continued to recognize the order. Furnish and Glenister (1964) [3] included the Bassleroceratidae in the Ellesmerocerida while Sweet (1964) [4] included its derivative, the Graciloceratidae, in the Oncocerida. Flower (e.g. 1976) [5] 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. [3] [4]

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.

Related Research Articles

The Discosorida are an order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the camerae (chambers) in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally. Siphuncle structure indicated that the Discosorida evolved directly from the Plectronoceratida rather than through the more developed Ellesmerocerida, as did the other orders. Finally and most diagnostic, discosorids developed a reinforcing, grommet-like structure in the septal opening of the siphuncle known as the bullette, formed by a thickening of the connecting ring as it draped around the folded back septal neck.

Plectronocerida order of molluscs

Plectronocerida is a primitive order from which subsequent cephalopod orders are ultimately derived.

Beekmanoceras is a small cephalopod from the Middle Canadian Epoch of New York with a loosely coiled, gyroconic, shell in which the whorls are not in contact and the siphuncle is on the inner or concave side of the whorl. Furnish and Glenister (1964) placed Beekmanoceras in the Trocholitidae (Tarphycerida), interpreting the curvature to be ventral side convex, i.e. exogastastric and the siphuncle to be dorsal. Flower (1964) included Beekmanoceras in the Ellesmeroceratidae believing the siphuncle to be ventral and the curvature to be endogastric with the ventral side concave.

The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the dorso-ventral dimension is slightly greater than the lateral, with close spaced sutures having shallow lateral lobes and a generally large tubular ventro-marginal siphuncle with concave segments and irregularly spaced diaphragms. Connecting rings are thick and layered, externally straight but thickening inwardly with the maximum near the middle of the segment so as to leave concave depressions on internal siphuncle molds. Septal necks are typically orthochoanitic but vary in length from almost absent (achoanitic) to reaching halfway to the previous septum (hemichoanitic) and may even slope inwardly (loxochoanitic).

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 20 million years.

Orthoceratoidea is a subclass, formerly considered an infraclass or a superorder, that comprises Cephalopoda orders that have orthoconic to slightly cyrtoconic shells and central to subcentral siphuncles in which there may be internal deposits. Currently, Orthoceratoidea comprises the orders Dissidocerida, Ascocerida, Pseudorthocerida, Lituitida and Orthocerida.

The Graciloceratidae is a family of nautiloid cephalopods from the Middle and Upper Ordovician belonging to the Oncocerida, characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled, orthochoantic marginal or subventral, tubular siphuncles.

Oncoceratidae family of molluscs

Oncoceratidae is a family of nauatiloid cephalopods in the order Oncocerida established by Hyatt, 1884, that range from the Middle Ordovician to the Upper Silurian.

The Bassleroceratidae is a family of gradually expanding, smooth ellesmerocerids with a slight to moderate exogastric curvature, subcircular to strongly compressed cross section, and ventral orthochaonitc siphuncle. The ventral side is typically more sharply rounded than the dorsal side and septa are close spaced. Connecting rings are thick and slightly expanded into the siphuncle, making the segments slightly concave; characteristic of the Ellesmerocerida.

The Tripteroceratidae is a family of depressed, straight to slightly curved nautiloid cephalopods from the middle and upper Ordovician with generally flattened venters and empty siphuncles with straight to inflated sedments included in the Oncocerida.

The Valcouroceratidae is a family within the Oncocerida, nautiloid cephalopods from the middle and upper Ordovician, established by Rousseau Flower in 1945.

Protcycloceratidae is an extinct family of slender, commonly annulate, members of the cephalopod order Ellesmerocerida that lived during the Early Ordovician.

The Lituitidae are a family of evolved tarphycerids characterized by a long orthoconic section that follows a coiled juvenile portion at the apex, along with a generally tubular siphuncle, which like that of the barrandeocerids is composed of thin connecting rings.

Bassleroceras is an elongate upwardly curved, exogastric, genus with the venter on the under side more sharply rounded than the dorsum on the upper. The siphuncle is ventral, composed of thick-walled tubular segments in which connection rings thicken in towardly as in both the Ellesmerocerida and primitive Tarphycerida.

Estonioceratidae family of molluscs

The Estonioceratidae are a family of loosely coiled tarphycerids in which the inner side of the whorls, which forms the dorsum, is rounded or flat with no impression, and in which the siphuncle, composed of thick tubular segments, is located ventrally. The Estonioceratidae seem to form a link between the ancestral Bassleroceratidae and the more tightly coiled Tarphyceratidae.

The Nautilitoidea is a superorder within the subclass Nautiloidea, comprising the phylogenetically related Nautilida, Oncocerida, and Tarphycerida.

Ellesmeroceras is the type genus for the Ellesmeroceratidae, a family of primitive nautiloid cephalopods, that is characterized by its small, generally compressed, gradually expanded, orthoconic shell, found in Lower Ordovician marine sediments. The septa are close spaced and the siphuncle is ventral, about 0.2 the diameter of the shell. Septal necks are typically orthochoanitic but may slant inwardly (loxochoanitic) or reach halfway to the previous septum (hemichoanitic). Connecting rings are thick. As common for the Ellesmerocerida, Ellesmeroceras has diaphragms within the siphuncle tube.

References

  1. 1 2 3 R. H. Flower and B. Kummel. 1950. A Classification of the Nautiloidea. Journal of Paleontology 24(5):604-616
  2. ↑ A. A. Shevyrev. 2006. The Cephalopod Macrosystem: A Historical Review, the Present State of Knowledge, and Unsolved Problems: 2. Classification of Nautiloid Cephalopods. Paleontological Journal 40(1)
  3. 1 2 Furnish W.M and Glenister, Brian F 1964, Nautiloidea -Ellesmerocerida. Treatise on Invertebrate Paleontology, Geol Soc of America and Univ Kansas Press (Teichert & Moore, Eds)
  4. 1 2 Sweet, Walter C. 1964 Nautiloidea- Oncocerida. Treatise on Invertebrate Paleontology , Geol Soc of America and Univ Kansas Press (Teichert & Moore, Eds)
  5. ↑ 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
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