Oncoceratidae

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Oncoceratidae
Temporal range: M Ord- U Sil
Oocerina plebeia.JPG
Oonocerina plebeia, Barrande from Slivenec, Prague, Czech Republic at the National Museum (Prague)
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order:† Oncocerida
Family:†Oncoceratidae
Hyatt, 1884

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.

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.

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.

The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.

Contents

Diagnosis

Oncoceratidae are characterized by generally compressed, cyrtoconic, and breviconic shells with an exogastric curvature such that the ventral profile is convex or more so than dorsal, and in which the siphuncle is generally empty and located ventral of the center. In primitive forms, the siphuncle in early growth stages is composed of tubular segments with almost straight suborthochoanitic septal necks, but becomes cyrtochoanitic with expanded segments in the later growth stages, and is expanded and cyrtochoanitic throughout in advanced forms. In a few advanced forms, the siphuncle is actinosiphonate. (Flower 1950, Sweet 1964)

Siphuncle Strand of tissue passing longitudinally through the shell of a cephalopod mollusk

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the walls dividing the chambers.

Evolution

The Oncoceratidae first appeared early in the Middle Ordovician (Sweet 1964) simultaneously with the Graciloceratidae, Tripteroceratidae, and Valcouroceratidae, derived from the Gracilocertidae.(Flower 1950, 1976)

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.

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 an oncocerid family from the middle and upper Ordovician, mainly of North America, consisting of genera characterized by exogastricly curved cyrtoconic and breviconic shells that change ontogeneticially from compressed to depressed or subtriangular and in which the siphuncle in ventral and actinosiphonate.

Some Middle Ordovician oncoceratids such as Richardsonoceras and Oonoceras are, however, externally more similar to Bassleroceras than to Graciloceras. Moreover, Richardsonoceras has been reported from the upper Lower Ordovician (Arenigian) of China, bringing its first appearance before the earliest known graciloceratids. Other oncoceratids such as Rhizoceras and Miamoceras show a greater affinity to the Graciloceratidae.

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.

The Oncoceratidae through Oncoceras is thought to be the most likely source for the slightly endogastric Ordovician Diestoceratidae (Sweet 1964) and through the Early Silurian Amphycertoceras, for the Acleistoceratidae. The Oncoceratidae also gave rise to the dominantly Devonian Brevicoceratidae and Siluro-devonian Nothoceratidae though Oonoceras and to the largely Devonian Polyelasmoceratidae through either Oonoceras or Oocerina.(Sweet 1964)

Oncoceras is a genus of oncocerids, family Oncoceratidae from the middle and upper Ordovician of North America and Europe.

The Acleistoceratidae is a family of oncocerids that contains genera characterized by depressed exogastric brevicones and cyrtocones that range from the Middle Silurian to the Middle Devonian. The siphuncle is broadly expanded, and in some actinosiphonate.

The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, England, where rocks from this period were first studied.

Subgroups

The Oncoceratidae can be subdivided into arbitrary and convenient subgroups based on morphologic similarity, based on illustrations in the Treatise K 1964 (figs 200–203, pp K285-K288). One comprising elongate slender forms is referred to as the Slender Oncoceratidae. The other, comprising generally short, breviconic forms is referred to as the Breviconic Oncoceratidae .

The Treatise on Invertebrate Paleontology 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 covering every phylum, class, order, family, and genus of fossil and extant invertebrate animals. The prehistoric invertebrates are described as to their taxonomy, morphology, paleoecology, stratigraphic and paleogeographic range. However, genera with no fossil record whatsoever have just a very brief listing.

Slender Oncoceratidae

Slender Oncoceratidae are those in the family Oncoceratidae, which have slender, commonly curved, shells. Some like Oocerina are gently curved, almost straight, and with only slight expansion. Others like Dunleithoceras are strongly curved with a more notable rate of expansion. Inclusion in this somewhat arbitrary category is based on illustrations in the Treatise Part K, 1964.

Breviconic Oncoceratidae

Breviconic Oncoceratidae comprise genera included in the family Oncoceratidae known from generally short, i.e. breviconic and often exogastrically curved shells. They are considered oncoceratids (nautiloid order Oncocerida) on the basis of having typically empty siphuncles ventral of the center that may be suborthochoanitic and tubular in the early growth stage and cyrtochoantic with expanded segments in later growth stages or entirely. Connecting rings are thin. Breviconic oncoceratids differ from slender oncoeratids only in the matter of relative length. Inclusion is based on descriptions and illustrations in Sweet 1964 on the Oncerida in the Treatise on Invertebrate Paleontology, Park K.

Included genera

Breviconic oncoceratid genera include:

Oncoceras ; compressed, curved brevicones, M-U Ord, N Am., Eu.
Beloitoceras ; compressed, curved brevicones, like Oncoceras, M-U Ord, N Am., Eu.
Metarizoceras ; slightly curved, compressed, rapidly expanding brevicons, M Sil. N Am.
Neumatoceras ; compressed brevicones with maximum height behind posterior end of body chamber, M-U Ord., N Am., Eu.
? Vaupella ; depressed, cyrtoconic brevicones with large ventral cytrochoanitic siphuncle, otherwise with characters of the family.

Related Research Articles

Ascocerida order of molluscs

The Ascocerida are comparatively small, bizarre Orthoceratoids known only from Ordovician and Silurian sediments in Europe and North America, uniquely characterized by a deciduous conch consisting of a longiconic juvenile portion and an inflated breviconic adult portion that separate sometime in maturity.

The Brevicoceratidae is a family of oncocerids that contains genera characterized by exogastric gyrocones, brevicones, and torticones. that tend to develop vestigial actinosiphonate deposits and subtriangular transverse sections. The Brevicoceratidae are derived from Oonoceras (Oncoceratidae) and range from the mid-Silurian to the Upper Devonian.

Osbornoceras is a genus of Lower Silurian cyrtoconic nautiloid cephalopods known from Ohio and possibly Manitoba, one of five general currently included in the oncocerid family Karoceratidae.

Acleistoceras is a genus of the oncocerid, nautiloid family Acleistoceratidae that lived in the shallow seas that covered much of North America during the Devonian; living from 409—383.7 mya, existing for approximately 25.3 million years.

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

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

Nothoceratidae is a family of nautiloid cephalopods in the orthoceratoid order Oncocerida in which shells are exogastrically or endogastrically breviconic, planospiral, or torticonic; often with a constricted or visored aperture; and a siphuncle commonly composed of concave segments and occupied by actinosiphonate deposits. Some ten genera have been described which lived during the time between the Early Silurian and Late Devonian. The ancestral form is probably Perimecoceras which is known from the Upper Silurian of central Europe and which is similar in external form the Oonoceras from the Oncoceratidae.


Blakeoceras is a nautiloid cephalopod from the Oncocerida family Nothoceratidae with a curved shell that lived in shallow seas from the Silurian to the Middle Devonian in what has become Europe.

<i>Oocerina</i> genus of molluscs

Oocerina is an extinct genus of nautiloid cephalopods that lived during the Late Silurian of Europe, Russia, and North America.

Kentlandoceras is a genus of middle Ordovician Oncocerids. Its shell is curved exogastrically, such that the ventral margin is longitudinally convex, but less so than in Loganoceras, and with a submarginal ventral siphuncle instead. The siphuncle in Loganoceras is subcentral. The related Romingoceras is more curved, also with a ventral siphuncle.

Danaoceras is a nautiloid cephalopod from the middle Silurian of central Europe included in the oncoceroid family Polyelasmoceratidae. Similar specimens from the middle Devonian of North America may belong.

Maelonoceras is a Late Ordovician - early Silurian oncocerid found in Ontario.

References

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