Endocerida

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m (Protected "Endocerida" [move=sysop])
m (The Endocerid Siphuncle: spelling Piloceratidae)
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== The Endocerid Siphuncle ==
== The Endocerid Siphuncle ==
The basic endocerid siphuncle has been introduced. Siphuncle segments in the Endocerida are straight, sinuous, or concave, and never expanded into the chambers as with the comtemporary [[Actinocerida|actinocerids]] and [[Discosorida|discosorids]]. Septal necks may be orthochoanitic, short; holochoanitic, reaching close to the previous septum; or macrochoanitic,  reaching beyond the previous septum  Connecting rings are thick and often show layering. With concave segments, connecting rings are thickened inwardly and leave depressions or concavities in siphuncle nternal molds.(1)(2)  
The basic endocerid siphuncle has been introduced. Siphuncle segments in the Endocerida are straight, sinuous, or concave, and never expanded into the chambers as with the comtemporary [[Actinocerida|actinocerids]] and [[Discosorida|discosorids]]. Septal necks may be orthochoanitic, short; holochoanitic, reaching close to the previous septum; or macrochoanitic,  reaching beyond the previous septum  Connecting rings are thick and often show layering. With concave segments, connecting rings are thickened inwardly and leave depressions or concavities in siphuncle nternal molds.(1)(2)  
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Endocones, with apeces pointing aft (adapically) develop in the after or apical portion of the siphuncle where they produce a balancing weight that compensates for the visceral mass forward in the body chamber and remaining portion of the siphuncle. This helps keep the shell (and animal) in a horizonal orientation during life. Endocones are typically penetrated by a narrow axial tube, the endosiphotube which often contains irregular diaphragms, reminiscent of the ellesmeroceratid ancestors.(1)(2)
Endocones, with apeces pointing aft (adapically) develop in the after or apical portion of the siphuncle where they produce a balancing weight that compensates for the visceral mass forward in the body chamber and remaining portion of the siphuncle. This helps keep the shell (and animal) in a horizonal orientation during life. Endocones are typically penetrated by a narrow axial tube, the endosiphotube which often contains irregular diaphragms, reminiscent of the ellesmeroceratid ancestors.(1)(2)
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In some, such as the endogastric [[Pilocertidae]] and essentially orthoconic [[Endoceratidae]] the endosiphuncle, comprising the structures within, is simple. In others, such as the [[Manchuroceratidae]], [[Emmonsoceratidae]]. [[Najacertidae]], and strange [[Allotrioceratidae]] the endosiphuncle is complex with additional structures. Principal among these are longitudial processs or partitions that project inward from the ventral or dorsal, and sometimes lateral margin of the siphuncle, about which the endocones form;  thin, dark, blade-like features bisecting primary structures; and what look like fine, often symmetrically postitioned, tubules. (1)(2)  
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In some, such as the endogastric [[Piloceratidae]] and essentially orthoconic [[Endoceratidae]] the endosiphuncle, comprising the structures within, is simple. In others, such as the [[Manchuroceratidae]], [[Emmonsoceratidae]]. [[Najacertidae]], and strange [[Allotrioceratidae]] the endosiphuncle is complex with additional structures. Principal among these are longitudial processs or partitions that project inward from the ventral or dorsal, and sometimes lateral margin of the siphuncle, about which the endocones form;  thin, dark, blade-like features bisecting primary structures; and what look like fine, often symmetrically postitioned, tubules. (1)(2)  
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Two suborders proposed by Flower in 1958 (4), the Proterocameroceratina and the Endoceratina are generally recognized, although not  in all taxonomies. The Proterocameroceratina are the earliest and include such genera as ''Proendoceras'', ''Clitendoceras'', ''Mcqueenoceras'' and ''Proterocameroceras'' The Proterocamerocerina gave rise in the early Middle Canadian (early Arenig) to the Endoceratina, possibly from ''Clitendoceras'', and to derived families within the suborder with more complex siphuncle interiors. In contrast the Endoceratina, although including the largest endocerids, remained internally simple. 
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Two suborders proposed by Flower in 1958 (4), the Proterocameroceratina and the Endoceratina are generally recognized, although not  in all taxonomies. The Proterocameroceratina are the earliest and include such genera as ''Proendoceras'', ''Clitendoceras'', ''Mcqueenoceras'' and ''Proterocameroceras'' The Proterocamerocerina gave rise in the early Middle Canadian (early Arenig) to the Endoceratina, possibly from ''Clitendoceras'', and to derived families within the suborder with more complex siphuncle interiors. In contrast the Endoceratina, although including the largest endocerids, remained internally simple.
==References==
==References==

Revision as of 21:09, 15 November 2009

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