Tarphycerida

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'''Tarphycerida''' are exogastrically coiled [[nautiloid]] [[cephalopod]]s known from the Lower [[Ordovician]] to the Upper [[Devonian]], derived from ''[[Bassleroceras]]'', or some similar form from the [[Ellesmerocerida]]. Early tarphycerids from the Lower [[Ordovician]] (middle and upper Canadian Epoch) have tubular [[siphuncle]]s with thick-walled,often layered connecting rings. The position of the siphuncle, a taxonomic indicator, may be ventral, central, or dorsal. Later, in the Middle Ordovician, connecting rings became thinner and homogeneous in some forms, resulting in what once was a separate order, the [[Barrandeocerina|Barrandeocerida]]. These later derivatives, found to have multiple tarphycerid ancestors are now encorporated within the [[Tarphycerida]]  
'''Tarphycerida''' are exogastrically coiled [[nautiloid]] [[cephalopod]]s known from the Lower [[Ordovician]] to the Upper [[Devonian]], derived from ''[[Bassleroceras]]'', or some similar form from the [[Ellesmerocerida]]. Early tarphycerids from the Lower [[Ordovician]] (middle and upper Canadian Epoch) have tubular [[siphuncle]]s with thick-walled,often layered connecting rings. The position of the siphuncle, a taxonomic indicator, may be ventral, central, or dorsal. Later, in the Middle Ordovician, connecting rings became thinner and homogeneous in some forms, resulting in what once was a separate order, the [[Barrandeocerina|Barrandeocerida]]. These later derivatives, found to have multiple tarphycerid ancestors are now encorporated within the [[Tarphycerida]]  
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==Evolution==
Tarphycerids were the first  coiled cephalopods, a condition that evolved again in the [[Nautilida]] and [[Ammonoidea]] and in a lesser but more diverse manner in the [[Oncocerida]].  The evolutionary sequence began with an exogastric form like Basslerocers, in which at some early stage the curvature continued beyond the basic arc and eventually grew for more than one volution, producing an open spiraled gyrocone. Here we have the first undeniable tarphycerid. A similar sequence can be shown form the nautilids and for the ammonoids.  
Tarphycerids were the first  coiled cephalopods, a condition that evolved again in the [[Nautilida]] and [[Ammonoidea]] and in a lesser but more diverse manner in the [[Oncocerida]].  The evolutionary sequence began with an exogastric form like Basslerocers, in which at some early stage the curvature continued beyond the basic arc and eventually grew for more than one volution, producing an open spiraled gyrocone. Here we have the first undeniable tarphycerid. A similar sequence can be shown form the nautilids and for the ammonoids.  
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==Taxonomy==
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The Tarphycerida contains 10 families, 11 if the Bickmoritidae are separated from the Barranceratidae in the suborder Barrandeocerina. The Lituitidae, which had been moved back and forth between the older Tarphycerida and Barrandeocerida, is now included in with the orthocerids.
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For the Tarphyceratidae, Estonioceratidae, Trocholitidae, and Ophidioceratidae that made up the original Tarphycerida, see [[Tarphycerin Families.]]  For  the families included in the original Barrandeocerida, beginning with the Barrandeoceratidae and Plectoceratidae, see [[Barandeocerine Families]]
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The Tarphycerida now contains about 11 families (12 if the Bassleroceratidae are included as Flower (1976) insisted) Four families, the Tarphyceratidae, [[Estonioceratidae]], [[Trocholitidae]], and [[Ophidioceratidae]] were included in the orginal Tarphycerida of Flower (1950) At that time Flower (1950) included the Bassleroceratidae along with the [[Graciloceratidae]] in the Bassleroceratida. Six addtional families come from the original Barrandeocerida (Flower 1959). They are the [[Barrandeoceratidae]], [[Plectoceratidae]], [[Apsidoceratidae]], [[Lechritrochoceratidae]], [[Uranoceratidae]], and [[Nephriticeratidae]]. The 11th family, all told, the [[Bickmoritidae]] are sometimes separated from the Barrandeoceratidae.
 
[[User: John M|JHM]] 8/16/09
[[User: John M|JHM]] 8/16/09

Revision as of 00:27, 17 December 2009

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