Orthoceratoidea

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Systematic Paleontology
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<u>Systematic Paleontology</u> <br>
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:Class: [[Cephalopoda]]
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Class: [[Cephalopoda]] <br>
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:Subclass: [[Nautiloidea]]
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Subclass: [[Nautiloidea]] <br>
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:Superorder: <u>Orthoceratoidea</u>
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Superorder: '''Orthoceratoidea''' <br>
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:Subtaxa: Orders
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Subtaxa: Orders <br>
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:: [[Orthocerida]]
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:[[Orthocerida]]
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:: [[Ascocerida]]
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:[[Ascocerida]]
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:: [[Bajkalocerida]]
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:[[Dissidocerida]]
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:: [[Dissidocerida]]
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:[[Pseudorthocerida]]
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:: [[Pseudorthocerida]]
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:: [[Lituitida]] unless [[Tarphycerida]]
 
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The Orthoceratoidea is a superorder within the Nautiloidea that combines several generally orthoconic orders in which the siphuncle, composed of thin conncecting rings, is central or subcentral and may contain annular deposits which may grow together and fuse into a  continuous internal lining, and which often have organic cameral deposits. The orders which have been included are the Orthocerida, Dissidocerida, Bajkalocerida, Ascocerida, Pseudorthocerida, and the tarphyceroid Lituitida, partly on the basis of its having an orthocerid-like apex.  
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The Orthoceratoidea is a superorder within the Nautiloidea that combines several generally orthoconic orders in which the siphuncle, composed of thin connecting rings, is central or subcentral and may contain annular deposits which may grow together and fuse into a  continuous internal lining, and which often have organic cameral deposits. The orders which have been included are the Orthocerida, Dissidocerida, Bajkalocerida, Ascocerida, Pseudorthocerida, and the tarphyceroid Lituitida, partly on the basis of its having an orthocerid-like apex.  
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The Orthocreatoidea as defined by Mary Wade (1988) included the  Orthocerida, Pseudorthocerida, and Ascocerida.   
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The Orthoceratoidea as defined by Mary Wade (1988) includes the  Orthocerida, Pseudorthocerida, and Ascocerida.   
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The Baltoceratidae, which have connecting rings thinner than in the typical Ellesmerocerida and straight or slightly expanded siphuncle segments have been reassigned to the Orthocerida (Kroger et al, 2007). Kröger (2008) divided the Orthoceratoidea (his subclass Orthoceratoidae) into two main groups. The first consists of the Ascocerida and Pseudorthocerida, which have a conical apex with a cicatrix,  The second consists of the Orthocerida and Lituitida which have a small spherical apex and lack a cicatrix. The Dissidocerida, not put in either group, are derived from rod-bearing Baltoceratidae.  
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The Baltoceratidae, which have connecting rings thinner than in the typical Ellesmerocerida and straight or slightly expanded siphuncle segments have been reassigned to the Orthocerida (Kröger et al, 2007).  
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In Shevyrev's taxomony (2004) the Orthoceratoidea, considered a subclass, includes  the Orthocerida, Ascoderida,  Dissidocerida and Bajkalocerida.  Pseudorthocerids are included in the Orthocerida.  The Bajkalocerida is another name for the Intejocerida.  
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Kröger (2008) divided the Orthoceratoidea (his subclass Orthoceratoidae) into two main groups. The first consists of the Ascocerida and Pseudorthocerida, which have a conical apex with a cicatrix,  The second consists of the Orthocerida and Lituitida which have a small spherical apex and lack a cicatrix. The Dissidocerida, not put in either group, are derived from rod-bearing Baltoceratidae.
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In Shevyrev's taxomony (2004) the Orthoceratoidea, considered a subclass, includes  the Orthocerida, Ascoderida,  Dissidocerida and Bajkalocerida.  Pseudorthocerids are included in the Orthocerida.  The Bajkalocerida, another name for the Intejocerida, is an association of families proposed by Balashov 1960, which Teichert (1964) included in the Endoceratoidea but which includes species better included in the Baltoceratidae.
The derivation of the Ascocerida and Pseudorthocerida is well understood, the Pseudorthocerida being the Silurian to Permian  Pseudorthoceratidae of Sweet (1964) which otherwise is polyphyletic according to Flower (1976)  if Ordovician families are included.  The Dissidocerida and Bajkalocerida are  thought to be closely related. The inclusion of the Lituitidae as the Lituitida is another matter.
The derivation of the Ascocerida and Pseudorthocerida is well understood, the Pseudorthocerida being the Silurian to Permian  Pseudorthoceratidae of Sweet (1964) which otherwise is polyphyletic according to Flower (1976)  if Ordovician families are included.  The Dissidocerida and Bajkalocerida are  thought to be closely related. The inclusion of the Lituitidae as the Lituitida is another matter.
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==Credits==
==Credits==
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*John M 4/24/10
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*John M 4/24/10 , 5/31/11

Latest revision as of 22:24, 31 May 2011

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