Oncoceratidae is a family of nauatiloid cephalopods in the order

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 ...

established by Hyatt, 1884, that range from the Middle

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

to the Upper

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

Diagnosis

Oncoceratidae are characterized by generally compressed, cyrtoconic, and breviconic shells with an exogastric curvature such that the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

profile is convex or more so than

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

, and in which the

siphuncle 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 ...

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 In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatr ...

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)

Evolution

The Oncoceratidae first appeared early in the

Middle 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. The ...

(Sweet 1964) simultaneously with the Graciloceratidae, Tripteroceratidae, and Valcouroceratidae, derived from the Gracilocertidae.(Flower 1950, 1976) Some Middle Ordovician oncoceratids such as ''Richardsonoceras'' and ''Oonoceras'' are, however, externally more similar to ''

Bassleroceras ''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 ring ...

'' than to '' Graciloceras.'' Moreover, ''Richardsonoceras'' has been reported from the upper

Lower 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. The ...

(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. The Oncoceratidae through ''

Oncoceras ''Oncoceras'' is a genus of oncocerids, family Oncoceratidae from the middle and upper Ordovician of North America and Europe. The shell, or conch, of ''Oncoceras'' is relatively short, a curved, compressed brevicone with a maximum width in the ...

'' 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 Acleistoceratidae is a family of oncocerids that contains genera characterized by depressed (or rarely compressed) exogastric brevicones and cyrtocones (Sweet, 1964 K398) that range from the Middle Silurian to the Middle Devonian. The siphu ...

. The Oncoceratidae also gave rise to the dominantly

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

Brevicoceratidae and Siluro-devonian Nothoceratidae through ''Oonoceras'' and to the largely Devonian Polyelasmoceratidae through either ''Oonoceras'' or ''Oocerina''.(Sweet 1964)

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 {{Taxobox , name = Slender Oncoceratidae , fossil_range = M Ord- U Sil , image = Oocerina plebeia.JPG , image_caption = ''Oonocerina plebeia'', Barrande from Slivenec, Prague, (Czech Republic) at the National Museum (Prague) , regnum = Anima ...

. The other, comprising generally short, breviconic forms is referred to as the Breviconic Oncoceratidae .

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

) on the basis of having typically empty

s ventral of the center that may be suborthochoanitic and tubular in the early growth stage and cyrtochoanitic 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: ''

''; 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.

References

*Flower 1950, in Flower & Kümmel, A Classification of the Nautiloidea, Journal of Paleontology 243 Sept 1950 *Flower 1976, Ordovician Cephalopod Faunas and Their Role in Correlation; The Ordovician System; proceedings of a palaeonotlogical Association symposium, Birmingham U.K. 1974. *Sweet, W.C. 1964. Nautiloidea -Oncocerida.

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 ...

Part K Nautiloidea, Teichert & Moore eds {{Taxonbar, from=Q7092083 Nautiloids Middle Ordovician first appearances Silurian extinctions