Ellesmeroceratidae

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Ellesmeroceratidae
Temporal range: U Cambrian - L Ordovician
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Ellesmerocerida
Family: Ellesmeroceratidae
Kobayashi, 1934

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). [1]

Evolution and phylogeny

The Ellesmeroceratidae have their derivation in the Plectronoceratidae, order Plectronocerida, in Trempealeauan stage of the Late Cambrian from which time 13 genera have been described. [2] [3] The earliest described, assigned to the Ellesmeroceratidae, is the early Trempealeauan Hunuanoceras, which comes from the lower part of the upper Yenchou Member of the Fengshan Formation in China. Hunuanoceras is a small endogastric cyrtocone resembling the anscestral Plectronoceras except for having resistant calcified connecting rings.

Hunuanoceras is followed by Eburoceras, which first appears in the upper part of the upper Yenchou and continues throughout the overlying Wanwankou Member of the Fengshan. The Wanwankou is middle and early upper Trempealeauan. The remaining eleven genera are restricted to the Wanwankou, except for Clarkoceras and Ectenolites , which persist into the Lower Ordovician. [2] Clarkoceras and Ectenolites provide the ancestry for the diverse ellesmerceratitds of the Early Ordovician, Gasconadian, and those that followed.

The Gasconadian was dominated to virtual exclusion by the Ellesmeroceratidae, which diversified during that time into a variety of forms and genera. [1] Some like Ellesmeroceras and Eremoceras were straight shelled, following the example of Ectenolites. Others like Dakeoceras and Burenoceras were endogastric in the sense of Clarkoceras. Gradations are found between elongate (longiconic) and short (breviconic) forms and between straight (orthoconic) and curved (cyrtoconic) forms, and between those with simple open apertures and those with apertures that have contracted.

The Ellesmeroceratidae gave rise within the Ellesmerocerida to the Protocycloceratidae, Bassleroceratidae, and possibly the Cylostomiceratidae in the early Canadian (late Gasconadian (?), Demingian) and to the Bathmoceratidae, and Cyrtocerinidae in the late Canadian (late Jeffersonian or Cassinian). The Ellesmeroceratidae also gave rise at about the close of the Gasconadian to the Endocerida, Tarphycerida, and to the Orthocerida through the ancestral Baltoceratidae, [4] [5] [6] [7] at which time they cease to be the dominant element in cephalopod faunas.

Related Research Articles

Nautiloid Extinct subclass of nautiloids

Nautiloids are a large and diverse group of marine cephalopods (Mollusca) belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and developed an extraordinary diversity of shell shapes and forms. Some 2,500 species of fossil nautiloids are known, but only a handful of species survive to the present day.

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 Extinct order of molluscs

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

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.

Ectenolites is a genus of small, slender, cylindrical Ellesmeroceratids that resemble Ellesmeroceras but are smaller and proportionally narrower. Septa, as typical for ellesmerocerids, are close spaced with shallow lobes on either flank. The body chamber is proportionally long, the shell itself slightly compressed. The dorsal side at the beginning of the shell, opposite the aperture and body chamber, is strongly convex so to produce a sense of endogastric curvature with the apex and siphuncle aligned.

Clarkoceras is a genus of breviconic ellesmerocerid cephalopods, one of only two genera known to have crossed from the Late Cambrian, Trempealeauan, into the Early Ordovician, Gasconadian. ; the other being Ectenolites.

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.

The Gasconadian Stage is the first stage of the Ordovician geologic period in North America and of the Lower Ordovician Canadian Epoch, coming immediately after the Late Cambrian Trempealeauan and preceding the middle Canadian Demingian Stage. The Gasconadian is equivalent to the European Tremadocian and roughly to the Skullrockian of the Ibexian series.

The Reudemannoceratidae are the ancestral and most primitive of the Discosorida, an order of cephalopods from the early Paleozoic. The Reudemannoceratidae produced generally medium-sized endogastric and almost straight shells with the siphuncle slightly ventral from the center.

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

Phragmoceratidae Extinct family of molluscs

The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian.

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

The cephalopods have a long geological history, with the first nautiloids found in late Cambrian strata, and purported stem-group representatives present in the earliest Cambrian lagerstätten.

Jiagouceras is a genus of early primitive cephalopods from the Upper Cambrian of China, assigned to the Plectronoceratidae. The shell is small, nearly straight with a slight endogastric curvature and compressed cross section. The siphuncle is close to the ventral margin, with segments expanded into the chambers.

Plectronoceratoidea is a superorder of primitive nautiloids from the Late Cambrian and Early Ordovician that include the ancestors of subsequent cephalopod orders. Included within are the exclusively Cambrian Plectronocerida, Protactinocerida, and Yanhecentida, and the Cambro-Ordovician Ellesmerocerida.

Paraplectronoceras is a genus of very early nautiloids from the middle Late Cambrian, named by Chen and Qi, 1979, type species Paraplectronoceras pyriforme, for small, endogastrically curved forms found in the upper Yenchou and Wanwankou members of the Fengshan Formation of northeastern China.

Shungtangenoceras is a conical plectronoceratoid cephalopod from the Upper Cambrian of north-eastern China, described by Sun (1937) as a primitive endoceroid. Because of its apparently poor preservation its ordinal and familial position is uncertain. It could be included in either the Plectronocerida, family Plectronoceratidae, or the Ellesmerocerida, family Ellesmeroceratidae. On the other hand, Teichert (1964) included Shungtangendoceras in the Ellesmoerocatidae.

Apocrinoceratidae constitutes a family of Middle Ordovician nautiloid cephalopods characterized by straight or slightly curved, transversely ribbed shells having siphuncles composed of expanded segments, short recurved septal necks, and thick connecting rings. Derivation is from the Protocycloceratidae, a family of ellesmerocerids, which differ in having straight or concave siphuncle segments, but are otherwise similar in form.

Acaroceratidae is family of Upper Cambrian (Trempealeauan) nautiloid cephalopods included in the Ellesmerocerida that contains two known genera, Acaroceras and Weishanuceras, both found in northern China.

Eburoceras is an early nautiloid cephalopod from the Upper Yenchau and Wanwankau, Upper Cambrian Trempealeauan of China, assigned to the Ellesmeroceratidae.

References

  1. 1 2 Flower, R.H. (1964). The Nautiloid Order Ellesmerocerida (Cephalopoda) (PDF). Memoirs. Socorro, NM: New Mexico Bureau of Mines and Mineral Resources. Retrieved 10 November 2011.
  2. 1 2 Chen, J. Y.; Teichert, C. (1983). "Cambrian cephalopods". Geology. 11 (11): 647–650. Bibcode:1983Geo....11..647J. doi:10.1130/0091-7613(1983)11<647:CC>2.0.CO;2. ISSN   0091-7613.
  3. Teichert, Curt (1988). "Main Features of Cephalopod Evolution". In Clarke, M.R.; Trueman, E.R. (eds.). The Mollusca, volume 12. Paleontology and neontology of cephalopods. Academic Press. ISBN   0-12-751412-0.
  4. Teichert, Curt (1964). "Endoceratoidea". In Raymond C. Moore (ed.). Treatise on Invertebrate Paleontology. Part K Mollusca 3. Geological Society of America and University of Kansas Press. ISBN   0-8137-3011-2.
  5. Furnish, W.M.; Glenister, Brian F. (1964). "Nautiloidea - Tarphycerida". In Raymond C. Moore (ed.). Treatise on Invertebrate Paleontology. Part K Mollusca 3. Geological Society of America and University of Kansas Press. ISBN   0-8137-3011-2.
  6. 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; Birmimgham, England, 1974. Cardiff: University of Wales Press and the National Museum of Wales for the Palaeontological Association. pp. 531–537. ISBN   0-7083-0582-2.
  7. Kröger, B. R.; Mutvei, H. (2005). "Nautiloids with Multiple Paired Muscle Scars from Lower-Middle Ordovician of Baltoscandia". Palaeontology. 48 (4): 781. doi:10.1111/j.1475-4983.2005.00478.x.