Sactoceras
Encyclopedia
Sactoceras is an extinct nautiloid cephalopod
that lived during the Ordovician
and Silurian
in what would become North America
, Europe
, and Asia
.
is Orthoceras richteri Barrande, 1874, which comes from the Upper Silurian Ludlow Series of the Prague Basin, Czech Republic. Hyatt named Sactoceras for actinocerid species in which siphuncle
segments were much reduced in diameter relative to the diameter of the shell, noting that the "siphon becomes approximately reduced . . . with age", which he interpreted as a "degradational senile shrinking". Barrande (according to Foord (1888)) considered this to indicate a reverson to the simple siphuncle of the Orthoceratidae
, which might be taken to indicate a relationship to the Proteoceratidae
.
Evans (2000) considered Sactoceras to be an orthocerid, placing it in the Pseudorthoceratoidea (originally Pseudorthoceratacea) of Flower and Caster, 1935, and in the family Sactoceratidae of Troedsson, 1926. The Pseudorthocerataceae is now generally regarded as a separate order, the Pseuorthocerida, within the superorder Orthoceratoidea of Wade, 1988.
Chambers (camerae) are moderately long with septal spacing on the order of one-third (1/3) the shell diameter. Sutures are straight, transvese. Septal concavity varies from species to species.
The siphuncle is central to subcentral in the early part of the phragmocone, but may diverge away from the center in later growth stages. Segments are expanded, increasing from diameters of around 3 to 4 mm at the septal foremina to a maximum width of around 12 to 14 mm. Septal necks are cyrtochoanitic, outwardly curved and recumbent. Siphuncle segments, in some, are faintly tear-shaped in outline with the narrow end pointing back toward the apex.
Deposits of organic calcite form at the septal formina which project forward into the subsequent chamber and line the inside of the siphuncle. These are more continuous on the ventral side of the siphuncle. Cameral deposits are also more extensive in the ventral half of the pragmocone.
to Europe
and Asia
.
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
that lived during the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
and Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
in what would become North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
.
Taxonomy
The genus Sactoceras was named by Hyatt (1884). The type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is Orthoceras richteri Barrande, 1874, which comes from the Upper Silurian Ludlow Series of the Prague Basin, Czech Republic. Hyatt named Sactoceras for actinocerid species in which siphuncle
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 Spirula...
segments were much reduced in diameter relative to the diameter of the shell, noting that the "siphon becomes approximately reduced . . . with age", which he interpreted as a "degradational senile shrinking". Barrande (according to Foord (1888)) considered this to indicate a reverson to the simple siphuncle of the Orthoceratidae
Orthoceratidae
Orthoceratidae, is an extinct family of actively mobile carnivorous cephalapods, subclass Nautiloidea, that lived in what would be North America, Europe, Asia, Africa, and Australia from the Ordovician through Triassic from 490—203.7 mya, existing for approximately .-Taxonomy:Orthoceratidae was...
, which might be taken to indicate a relationship to the Proteoceratidae
Proteoceratidae
Proteoceratidae is an extinct family of actively mobile aquatic carnivorous cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, South America and North America during the Ordovician living from 490—445.6 Ma, existing for approximately...
.
Evans (2000) considered Sactoceras to be an orthocerid, placing it in the Pseudorthoceratoidea (originally Pseudorthoceratacea) of Flower and Caster, 1935, and in the family Sactoceratidae of Troedsson, 1926. The Pseudorthocerataceae is now generally regarded as a separate order, the Pseuorthocerida, within the superorder Orthoceratoidea of Wade, 1988.
Morphology
Sactoceras is orthoconic, essentially straight-shelled. The cross section of the shell (or conch) and that of the siphuncle are essentially circular. The shell is moderate in size, reaching diameters of 35mm or so, and expanding at a rate of around 6 to 9 degrees.Chambers (camerae) are moderately long with septal spacing on the order of one-third (1/3) the shell diameter. Sutures are straight, transvese. Septal concavity varies from species to species.
The siphuncle is central to subcentral in the early part of the phragmocone, but may diverge away from the center in later growth stages. Segments are expanded, increasing from diameters of around 3 to 4 mm at the septal foremina to a maximum width of around 12 to 14 mm. Septal necks are cyrtochoanitic, outwardly curved and recumbent. Siphuncle segments, in some, are faintly tear-shaped in outline with the narrow end pointing back toward the apex.
Deposits of organic calcite form at the septal formina which project forward into the subsequent chamber and line the inside of the siphuncle. These are more continuous on the ventral side of the siphuncle. Cameral deposits are also more extensive in the ventral half of the pragmocone.
Fossil distribution
Fossil distribution is found from North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
to Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
.