Actinoceratidae

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Actinoceratidae
Temporal range: Middle Ordovician - Lower Silurian
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Actinocerida
Family: Actinoceratidae
Saemann (1853)
Genera

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The Actinoceriatidae are a family of actinocerids named by Saemann in 1853 for those that grew to have large shells with blunt apices and large siphuncles with widely expanded segments and a generally arcuate endosiphucular canal system. [1] Their range is from the upper Middle Ordovician to the Lower Silurian. Actinocerids are generally straight-shelled nautiloid cephalopods with a siphuncle composed of expanded segments, typically with thin connecting rings, in which the internal deposits are penetrated by a system of canals

Actinoceratids are derived from Wutinoceras , possibly through an early Armenoceras or through Nybyoceras [2] and give rise to Lambeoceras and to the Huroniidae. [ citation needed ]

Seven genera are included in the Actinoceratidae, Actinoceras , Floweroceras , Kochoceras , Leurorthoceras , Paractinoceras , Saffordoceras , and Troostoceras . [1] Actinoceras is the earliest but with a range that carries it into the Lower Silurian. Troostoceras followed by Saffordoceras are later Middle Ordovician genera related to early Actinoceras. Kochoceras followed by Floweroceras are Upper Ordovian genera related to later Actinoceras. Leurothoceras and Paractinoceras, both from the Upper Ordovician, are shown to have their source in Middle Ordovician actinoceratids.

Paractinoceras is probably the most distinct actinoceratid from Actinoceras. Paractinoceras has a long, straight, slender shell and a siphuncle that starts off like that in Actinoceras, but becomes narrow like that in Ormoceras in the anterior part of the phragmocone. [1] Kochoceras has a large blunt shell that expands more rapidly than Actinoceras and is strongly flattened on the ventral side causing possible confusion with Lambeoceras to casual observation. Floweroceras is doubtfully distinct from Kochoceras. [2]

Leurothoceras is synonymous with Actinoceras ; Saffordoceras and Troostoceras are closely related. [2]

Related Research Articles

Bactritida Fossil order of cephalopods

The Bactritida are a small order of more or less straight-shelled (orthoconic) cephalopods that first appeared during the Emsian stage of the Devonian period with questionable origins in Pragian stage before 409 million years ago, and persisted until Carnian pluvial event in the upper middle Carnian stage of the Triassic period. They are considered ancestors of the ammonoids, as well as of the coleoids.

Huronia is an actinocerid genus included in the Huroniidae along with Discoactinoceras and Huroniella,(Teichert 1964). Huronia is characterized by long siphuncle segments with the free part of the connecting rings only slightly inflated and by a narrow central canal and strongly curved radial canals located in the anterior part of each siphuncle segment

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.

Actinoceras is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician. It is an extinct genus of nautiloid cephalopod that thrived in the warm waters of the United States during the Paleozoic era.

<i>Ormoceras</i> Extinct genus of molluscs

Ormoceras is an actinocerid nautiloid genus and type for the family Ormoceratidae, found in North America from the late Chazyan through the early Cincinnatian of the Middle and Upper Ordovician, but which continued through the Devonian worldwide.

Lambeoceras is a genus of large actinocerids with a convexly lenticular cross section from the Upper Ordovician of North America and the sole representative of the family Lambeoceratidae.

Armenoceras is a genus of actinocerid nautiloid cephalopods whose fossils ranged from the late Whiterockian Stage in the early Middle Ordovician, through the remainder of the period and on into the Upper Silurian. It is the type genus of the family Armenoceratidae.

Oncocerida Extinct order of nautiloids

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.

Bathmoceras is a primitive cephalopod genus from the Middle and Upper Ordovician. It is a member of the order Cyrtocerinida and is the only genus in the family Bathmoceratidae.

The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial canals and a narrow space along the inner side of the connecting ring known as a paraspatium. Septal necks are generally short and cyrtochoanitic, some being recumbent, some hook shaped. Most grew to lengths of about 60 to 90 cm but some, like the Huroniidae of the Silurian grew significantly larger.

Slender Oncoceratidae Group of nautiloids

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.

Sactoceras is an extinct nautiloid cephalopod that lived during the Ordovician and Silurian in what would become North America, Europe, and Asia.

Oncoceratidae Extinct family of nautiloids

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.

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.

The Wutinoceratidae are a family of early actinocerids defined by Shimazu and Obata in 1938 for actinocerids with thick connecting rings and a complex irregular canal system. Actinocerids are generally straight shelled nautiloid cephalopods with a siphuncle composed of expanded segments, typically with thin connecting rings, in which the internal deposits are penetrated by a system of canals.

Armenoceratidae Extinct family of molluscs

The Armenoceratidae are a family of early Paleozoic nautiloid cephalopods belonging to the order Actinocerida.

Wutinoceras is a genus of now extinct nautiloid cephalopods of the Wutinoceratidae family. It exhibits orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments.

Nybyoceras is an actinocerid genus assigned to the Armenoceratidae and similar to Armenoceras except for having a siphuncle close to the ventral side of the shell.

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

Kochoceras is an extinct nautiloid genus from the later Ordovician belonging to the family Actinoceratidae and found in North America.

References

  1. 1 2 3 Teichert 1964. Actinoceratoidea, Treatise on Invertebrate Paleontology, part K.(Nautiloidea)
  2. 1 2 3 Flower 1957.Studies of the Actinoceratida; Memoir 2; New Mexico Bureau of Mines and Mineral Resources, Socorro, NM