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Oncocerida

January 01, 1970

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[1]), in which the connecting rings are thin and siphuncle segments are variably expanded (Flower, 1950). 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 (Sweet, 1964).

Oncocerida
Temporal range: Middle Ordovician–Lower Carboniferous
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: †Oncocerida
Flower, 1950
Life reconstruction of Cyrtoceras sp

Physical characteristics edit

The shells of oncocerids are primarily somewhat compressed cyrtoconic brevicones. More advanced forms include gyrocones, serpenticones, torticones, and elongate orthocones and cyrtocones, reflective of the different families and genera (Flower, 1950; Sweet, 1964).

The siphuncle in the Oncocerida is commonly located at or near the ventral margin. Connecting rings are most commonly thin and structureless but in certain derived forms may become actinosiphonate with inwardly projecting radial lamellae. The juvenile segments in early genera are straight and tubular, with short orthochoanitic septal necks inherited from the Bassleroceratidae. Later in the mature stages of early forms and throughout in the more advanced the connecting rings are inflated with cyrtochoanitic septal necks, giving what can be described as a "beaded" or "ellipsoidal" appearance (Sweet, 1964).

Evolution and diversity edit

The Oncocerida are thought to be derived from the Bassleroceratidae through Graciloceras as a result of a thinning of the connecting rings in the siphuncle (Flower, 1976).

Oncocerids reached their greatest generic diversity in the Middle Silurian with some 43 genera representing nine families (Sweet, 1964), the most at any time. Of these 43 or so genera, about 38 were new, a recovery from a precipitous decline in the Late Ordovician and Early Silurian. A second period of greater diversity occurred in the Middle Devonian with eight families represented by some 37 genera, following a second decline after the Middle Silurian. After this the order declined until its extinction in the Early Carboniferous (Mississippian).

Near the beginning of the Devonian and well before its end, the Oncocerida gave rise to the Rutoceratidae (Flower, 1976; Kümmel, 1964), which form the root stock of the Nautilida, which among its members includes the modern Nautilus and Allonautilus.

Distribution and range edit

Oncocerids are well known as fossils from the later Ordovician, Silurian, and Devonian in North America, Europe, and Australia, and to a lesser extent from parts of Asia, after which the order declined into the Mississippian and reached its end by the Pennsylvanian (late Carboniferous) (Flower, 1976; Sweet, 1964).

Taxonomy edit

Families in the Oncocerida, according to the Treatise on Invertebrate Paleontology, follow with the number of genera in each shown in parentheses, along with the stratigraphic range.

Descendants edit

According to more current thinking, e.g. Flower, Teichert, and Kümmel, the Oncocerida gave rise to the Rutoceratidae which form the root stock of the Nautilida, which after a number of iterations, ends up with the modern Nautilus and Allonautilus.

References edit

  1. ^ T. B. Leonova; A. Yu. Shchedukhin (2020). "Asselian-Sakmarian nautiloids of the Shakh-Tau reef (Bashkortostan)". Paleontological Journal. 54 (10): 1113–1134. doi:10.1134/S0031030120100044.
  • Flower, R.H. in Flower and Kümmel Jr 1950; A Classification of the Nautiloidea; Journal of Paleontology, Vol 24, no 5, pp 604–616, Sept 1950
  • Flower, R.H. 1976; Ordovician Cephalopod Faunas and Their Role in Correlation, pp 523–552 in The Ordovician System: proceedings of a Paleontological Association symposium; Bassett, M.G. Ed.
  • Kümmel,B. 1964; Nautiloidea -Nautilida; Treatise on Invertebrate Paleontology, PartK, R.C. Moore Ed.
  • Sweet, W.C. 1964; Nautiloidea -Oncocerida; Treatise on Invertebrate Paleontology, PartK, R.C. Moore Ed.

January 01, 1970
oncocerida, comprise, diverse, group, generally, small, nautiloid, cephalopods, known, from, middle, ordovician, mississippian, early, carboniferous, possible, member, known, from, early, permian, which, connecting, rings, thin, siphuncle, segments, variably, . 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 1 in which the connecting rings are thin and siphuncle segments are variably expanded Flower 1950 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 Sweet 1964 OncoceridaTemporal range Middle Ordovician Lower Carboniferous PreꞒ Ꞓ O S D C P T J K Pg N Scientific classification Domain Eukaryota Kingdom Animalia Phylum Mollusca Class Cephalopoda Subclass Nautiloidea Order OncoceridaFlower 1950 Life reconstruction of Cyrtoceras sp Contents 1 Physical characteristics 2 Evolution and diversity 3 Distribution and range 4 Taxonomy 5 Descendants 6 ReferencesPhysical characteristics editThe shells of oncocerids are primarily somewhat compressed cyrtoconic brevicones More advanced forms include gyrocones serpenticones torticones and elongate orthocones and cyrtocones reflective of the different families and genera Flower 1950 Sweet 1964 The siphuncle in the Oncocerida is commonly located at or near the ventral margin Connecting rings are most commonly thin and structureless but in certain derived forms may become actinosiphonate with inwardly projecting radial lamellae The juvenile segments in early genera are straight and tubular with short orthochoanitic septal necks inherited from the Bassleroceratidae Later in the mature stages of early forms and throughout in the more advanced the connecting rings are inflated with cyrtochoanitic septal necks giving what can be described as a beaded or ellipsoidal appearance Sweet 1964 Evolution and diversity editThe Oncocerida are thought to be derived from the Bassleroceratidae through Graciloceras as a result of a thinning of the connecting rings in the siphuncle Flower 1976 Oncocerids reached their greatest generic diversity in the Middle Silurian with some 43 genera representing nine families Sweet 1964 the most at any time Of these 43 or so genera about 38 were new a recovery from a precipitous decline in the Late Ordovician and Early Silurian A second period of greater diversity occurred in the Middle Devonian with eight families represented by some 37 genera following a second decline after the Middle Silurian After this the order declined until its extinction in the Early Carboniferous Mississippian Near the beginning of the Devonian and well before its end the Oncocerida gave rise to the Rutoceratidae Flower 1976 Kummel 1964 which form the root stock of the Nautilida which among its members includes the modern Nautilus and Allonautilus Distribution and range editOncocerids are well known as fossils from the later Ordovician Silurian and Devonian in North America Europe and Australia and to a lesser extent from parts of Asia after which the order declined into the Mississippian and reached its end by the Pennsylvanian late Carboniferous Flower 1976 Sweet 1964 Taxonomy editFamilies in the Oncocerida according to the Treatise on Invertebrate Paleontology follow with the number of genera in each shown in parentheses along with the stratigraphic range Graciloceratidae 4 M U Ord Tripteroceratidae 5 M U Ord Valcouroceratidae 8 M U Ord Diestoceratidae 5 M U Ord Oncoceratidae 24 M Ord U Sil Jovellaniidae 5 U Ord M Sil L Dev Nothoceratidae 10 L Sil U Dev Karoceratidae 3 L M Sil L Dev Hemiphragmoceratidae 5 M U Sil M Dev Acleistoceratidae 22 M Sil M Dev Polyelasmoceratidae 13 M Sil U Dev Brevicoceratidae 17 M Sil U Dev Poterioceratidae 7 L Dev L Carb Tripleuroceratidae 2 L Dev M Dev L Carb Archiacoceratidae 3 M Dev Descendants editAccording to more current thinking e g Flower Teichert and Kummel the Oncocerida gave rise to the Rutoceratidae which form the root stock of the Nautilida which after a number of iterations ends up with the modern Nautilus and Allonautilus References edit T B Leonova A Yu Shchedukhin 2020 Asselian Sakmarian nautiloids of the Shakh Tau reef Bashkortostan Paleontological Journal 54 10 1113 1134 doi 10 1134 S0031030120100044 Flower R H in Flower and Kummel Jr 1950 A Classification of the Nautiloidea Journal of Paleontology Vol 24 no 5 pp 604 616 Sept 1950 Flower R H 1976 Ordovician Cephalopod Faunas and Their Role in Correlation pp 523 552 in The Ordovician System proceedings of a Paleontological Association symposium Bassett M G Ed Kummel B 1964 Nautiloidea Nautilida Treatise on Invertebrate Paleontology PartK R C Moore Ed Sweet W C 1964 Nautiloidea Oncocerida Treatise on Invertebrate Paleontology PartK R C Moore Ed Retrieved from https en wikipedia org w index php title Oncocerida amp oldid 1057839885, wikipedia, wiki, book, books, library,

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