Pachendoceras

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'''''Pachendoceras''''' is a relatively large ellesmeroceratid, [[Early Ordovician]], [[Gasconadian]] (Tremedoc) in age, which is thought to be the progenitor of the [[Endocerida|endocerids]]
'''''Pachendoceras''''' is a relatively large ellesmeroceratid, [[Early Ordovician]], [[Gasconadian]] (Tremedoc) in age, which is thought to be the progenitor of the [[Endocerida|endocerids]]
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Named by Ulrich and Foerste in 1936, ''Pachendoceras'' produced a large, almost tubular orthoconic shell with a slightly depressed subcircular section, straight sutures, and large ventral siphuncle. The siphincle which is composed of tubular or faintly concave segments, contains elongate, assymetric diaphragms that tend to be concentrated in the apical  portion.[1][2] In general aspect, ''Pachendoceras'' more closely resembles Middle and Upper Canadian (Epoch) endocerids than it does the contemporary ellesmeroceratids.
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Named by Ulrich and Foerste in 1936, ''Pachendoceras'' produced a large, almost tubular orthoconic shell with a slightly depressed subcircular section, straight sutures, and large ventral siphuncle. The siphincle which is composed of tubular or faintly concave segments, contains elongate, assymetric diaphragms that tend to be concentrated in the apical  portion.[1][2] In general aspect, ''Pachendoceras'' more closely resembles Middle and Upper [[Canadian Epoch|Canadian]] endocerids than it does the contemporary ellesmeroceratids.
Flower and Kummel(1950)[3]included ''Pachendoceras'' in the [[Baltoceratidae]] because of its straight sutures and somewhat depressed section, where it was retained in the Treatise[2], in spite of its early, Gasconadian, age.  Meanwhile Flower in 1964 [1], referring to its age which predates the later Lower and Middle Ordovician baltoceratids and to its suphunclar diaphragms which are therein absent, removed ''Pachendoceras'' to its contemporary [[Ellesmeroceratidae]] in which it shares primary characters.
Flower and Kummel(1950)[3]included ''Pachendoceras'' in the [[Baltoceratidae]] because of its straight sutures and somewhat depressed section, where it was retained in the Treatise[2], in spite of its early, Gasconadian, age.  Meanwhile Flower in 1964 [1], referring to its age which predates the later Lower and Middle Ordovician baltoceratids and to its suphunclar diaphragms which are therein absent, removed ''Pachendoceras'' to its contemporary [[Ellesmeroceratidae]] in which it shares primary characters.
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* [1]Flower 1964: The Nautiloid Order Ellesmeroceratida (Cephalopoda), Memoir 12; New Mexico Bureau of Mines and Mineral Resources, Socorro.  
* [1]Flower 1964: The Nautiloid Order Ellesmeroceratida (Cephalopoda), Memoir 12; New Mexico Bureau of Mines and Mineral Resources, Socorro.  
* [2]Furnish and Glenister, 1964: Nautiloidea - Ellesmerocerida; Treatise on Invertebrate Paleontology, Part K, Mollusca 3, R.C. Moore (Ed)  
* [2]Furnish and Glenister, 1964: Nautiloidea - Ellesmerocerida; Treatise on Invertebrate Paleontology, Part K, Mollusca 3, R.C. Moore (Ed)  
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* [3]Flower and Kummel 1950: A Classification  of the Nautiloidea; Jour Paleontology, 34(5) 604-616, Sept.   
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* [3]Flower and Kummel 1950: A Classification  of the Nautiloidea; Jour Paleontology, 24(5) 604-616, Sept.   
J McD 11/14/09
J McD 11/14/09

Revision as of 15:35, 14 November 2009

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