Actinocerida

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(revised general description as morphologic description, include siphuncle details there in)
(Moved classification to near the top, included list of families.)
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'''Actinocrids''' are generally straight shelled cephalopods with siphuncles composed of expanded segments in which internal deposits formed contain a canal system which connect to a seam along the inner side of the connecting rings known as a parispatium. Siphuncles vary in position from resting on the ventral margin to slightly below the center. Connecting rings are typically thin and septal necks are cytrochoanitic (outwardly curved) to recumbent. Shells vary is cross section from almost circular to very broad with acutly angles lateral edges. Cameral deposits, especially in the apical portion, are common.(Flower 1957, Teichert 1964)   
'''Actinocrids''' are generally straight shelled cephalopods with siphuncles composed of expanded segments in which internal deposits formed contain a canal system which connect to a seam along the inner side of the connecting rings known as a parispatium. Siphuncles vary in position from resting on the ventral margin to slightly below the center. Connecting rings are typically thin and septal necks are cytrochoanitic (outwardly curved) to recumbent. Shells vary is cross section from almost circular to very broad with acutly angles lateral edges. Cameral deposits, especially in the apical portion, are common.(Flower 1957, Teichert 1964)   
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=== Siphuncle Details ===
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==== Siphuncle Details ====
The internal deposits found in the siphuncle form at the septal foramina and grow forward and back to meet about halfway in each segment but in the mid portion do not attach to connecting ring, leaving instead a space or seam which is the parispatium. The parispatium is connected to a central canal system that runs the length of the siphuncle by a system of radial canals. The radial canals are found in different configurations that have been used in determining different families and genera. Parispatia have not been identified for sure in all actinocerid specimens and have also been noted in some pseudorthocerids. (Flower 1957, Teichert 1964)  
The internal deposits found in the siphuncle form at the septal foramina and grow forward and back to meet about halfway in each segment but in the mid portion do not attach to connecting ring, leaving instead a space or seam which is the parispatium. The parispatium is connected to a central canal system that runs the length of the siphuncle by a system of radial canals. The radial canals are found in different configurations that have been used in determining different families and genera. Parispatia have not been identified for sure in all actinocerid specimens and have also been noted in some pseudorthocerids. (Flower 1957, Teichert 1964)  
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== Classification ==
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'''Taxonomic position of the Actinocerida''' <br/>
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Russeau Flower (1957) considered the Actinocerida to be part of the [[Nautiloidea]], and no more uniquely distinct than any other order in the subclass. This perspective is followed here. This differs from the view of Curt Teichert (1964)  in which the actinocerids and endocerids are placed  in their own respective subclasses, Actinoceratoidea and Endoceratoidea.
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''' Taxonomy''' <br/>
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The Actinocerida includes nine families, shown hare, along with some 28 genera and numerous species. Included families are: <br/>
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:[[Wutinoceratidae]], ancestral <br/>
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::[[Actinoceratidae]], with derivatives <br/>
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:::[[Lambeoceratidae]] <br/>
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:::[[Huroniidae]] <br/>
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::[[Armenoceratidae]], with derivative<br/>     
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:::[[Gonioceratidae]] <br/>
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::[[Ormoceratidae]], with possible derivative <br/>
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::: [[Carbactinoceratidae]], and <br/>
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::Polydesmiadae. Position uncertain <br/>
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For a run down of all published subtaxa included in the Actinocerida see [[Actinocerid dendrogram]] page.
==Origin and Range==
==Origin and Range==
Actinocerids have their beginning near the end of the Canadian epoch (late Arenigian) and became plentiful during the Whiterockian epoch (early Middle Ordovician ). They diversified quickly and were at their greatest abundance during the Middle and Late Ordovician, then declined in the early Silurian and became a minor constituent of cephalopod faunas through the Devonian. Carboniferous forms previously identified as actinocerids have been reassigned to the Pseudorthocerida. (Flower 1857, 1968, 1976, Teichert 1964) As such, it is doubtful that they survived the extinction event at the transition from the Devonian to the Carboniferous.
Actinocerids have their beginning near the end of the Canadian epoch (late Arenigian) and became plentiful during the Whiterockian epoch (early Middle Ordovician ). They diversified quickly and were at their greatest abundance during the Middle and Late Ordovician, then declined in the early Silurian and became a minor constituent of cephalopod faunas through the Devonian. Carboniferous forms previously identified as actinocerids have been reassigned to the Pseudorthocerida. (Flower 1857, 1968, 1976, Teichert 1964) As such, it is doubtful that they survived the extinction event at the transition from the Devonian to the Carboniferous.
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The origin of the actinocerids remains uncertain. The Georginidae found in Northern Australia in the Cassinian Coolbah Formation and in China are the earliest known and may be the ancestral stock for the rest of the order. Their derivation remains a mystery. ''[[Bathmoceras]]'', a late Canadian ellesmerocerid and only representative of the Bathmoceratidae, has been suggested as ancestral based on the lobate inward projections of the connecting rings. An origin in the Trempealeauan (Late Cambrian) [[Protactinocerida]] has been suggested, but since no Protactinocerida are known to have crossed into the Ordovician, this seems unlikely. (Flower 1968, 1976; Wade 1988)
The origin of the actinocerids remains uncertain. The Georginidae found in Northern Australia in the Cassinian Coolbah Formation and in China are the earliest known and may be the ancestral stock for the rest of the order. Their derivation remains a mystery. ''[[Bathmoceras]]'', a late Canadian ellesmerocerid and only representative of the Bathmoceratidae, has been suggested as ancestral based on the lobate inward projections of the connecting rings. An origin in the Trempealeauan (Late Cambrian) [[Protactinocerida]] has been suggested, but since no Protactinocerida are known to have crossed into the Ordovician, this seems unlikely. (Flower 1968, 1976; Wade 1988)
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Nothing is known of their soft part anatomy, although some conjecture can be made based on their being cephalopods. They probably had a hyponome (funnel) for jet swimming. Their central nervous system was probably fairly well developed as were their senses. But whether their eyes had lenses like modern squid and octopus or were like the pin-hole-camera eyes of ''Nautilus'' is unknown. They probably had 10 arms, like ''Michelinoceras'', but no direct evidence has yet been found.
Nothing is known of their soft part anatomy, although some conjecture can be made based on their being cephalopods. They probably had a hyponome (funnel) for jet swimming. Their central nervous system was probably fairly well developed as were their senses. But whether their eyes had lenses like modern squid and octopus or were like the pin-hole-camera eyes of ''Nautilus'' is unknown. They probably had 10 arms, like ''Michelinoceras'', but no direct evidence has yet been found.
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== Classification ==
 
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Flower (Rousseau H) considered the Actinocerida to be part of the Nautiloidea, and did not consider them any more distinct than any other order in the subclass. That perspective is followed here. Curt Teichert on the other hand considered the actinocerids and endocerids sufficiently distinct to place them in their own respective subclasses, Actinoceratoidea and Endoceratoidea.
 
== Evolution==
== Evolution==
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The actinoceratids gave rise to ''Lambeoceras'' of the Red River faunas and to ''Huronia'' through ''Kochoceras''. ''Lambeoceras'' is the sole genus of the Lambeocertidae. ''Huronia'' and ''Huroniella'' join to form the Huroniadae. (ibid)
The actinoceratids gave rise to ''Lambeoceras'' of the Red River faunas and to ''Huronia'' through ''Kochoceras''. ''Lambeoceras'' is the sole genus of the Lambeocertidae. ''Huronia'' and ''Huroniella'' join to form the Huroniadae. (ibid)
   
   
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==Taxonomy==
 
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The Actinocerida includes nine families, shown hare, along with some 28 genera and numerous species.
 
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Included families are: <br/>
 
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:[[Wutinoceratidae]], ancestral <br/>
 
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::[[Actinoceratidae]], with derivatives <br/>
 
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:::[[Lambeoceratidae]] <br/>
 
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:::[[Huroniidae]] <br/>
 
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::[[Armenoceratidae]], with derivative<br/>     
 
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:::[[Gonioceratidae]] <br/>
 
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:: [[Ormoceratidae]], with possible derivative <br/>
 
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::: [[Carbactinoceratidae]] <br/>
 
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::Family Polydesmiadae. Position uncertain <br/>
 
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For a run down of all published subtaxa included in the Actinocerida see [[Actinocerid dendrogram]] page.
 
==References==
==References==

Revision as of 14:37, 8 December 2012

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