Actinocerida

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(Moved classification to near the top, included list of families.)
(Moved Biology and lifestyle to the end)
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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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==Biology and Lifestyle==
 
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Actinocerids were bottom dwellers, stalking prey or waiting in ambush. They evolved to fill different niches and physical conditions involving current and substrate. The endosiphuncular and cameral deposits concentrated more toward the apical end would have provided the primary balance to the visceral mass of the living animal in the body chamber and thus indicates a primary horizontal orientation. Actinocerids may not have been able to attain a high positive buoyance, having considerable mass in the form of internal deposits and close spaced septa, but they may have been able to attain enough positive buoyancy to rise off the bottom before either becoming neutrally buoyant or settling down again. The ability to evacuate or flood as many chambers as possible would have decreased the time needed for such maneuvers. The ability to shift ballast or selectively add or reduce weight would have further facilitated their mobility.
 
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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.
 
== Evolution==
== Evolution==
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The wutinocerids (Wutinoceratidae) gave rise to the Armenoceratidae near the end of the Whiterockian through ''Wutinoceras'' and to the Ormoceratidae in the Chazyan through ''Adamsoceras''. ''Cyrtonybyoceras'' is not known to have left any descendants.  ''Wutinoceras'' may also be ancestral to ''Polydesmia'' and thus ''Ordosoceras'' found only in Asia. (ibid)
The wutinocerids (Wutinoceratidae) gave rise to the Armenoceratidae near the end of the Whiterockian through ''Wutinoceras'' and to the Ormoceratidae in the Chazyan through ''Adamsoceras''. ''Cyrtonybyoceras'' is not known to have left any descendants.  ''Wutinoceras'' may also be ancestral to ''Polydesmia'' and thus ''Ordosoceras'' found only in Asia. (ibid)
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The armenocerids, based on internal details of the siphuncle, through an early ''Armenoceras'', gave rise to the Gonioceratidae in the Chazyan. The Gonioceratidae are represented solely by the genus ''Gonioceras'' which is  restricted to the Middle Ordovician. (ibid)
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The armenocerids,based on internal details of the siphuncle, through an early ''Armenoceras'', gave rise to the Gonioceratidae in the Chazyan. The Gonioceratidae are represented solely by the genus ''Gonioceras'' which is  restricted to the Middle Ordovician. (ibid)
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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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==Biology and Lifestyle==
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Actinocerids were bottom dwellers, stalking prey or waiting in ambush. They evolved to fill different niches and physical conditions involving current and substrate. The endosiphuncular and cameral deposits concentrated more toward the apical end would have provided the primary balance to the visceral mass of the living animal in the body chamber and thus indicates a primary horizontal orientation. Actinocerids may not have been able to attain a high positive buoyance, having considerable mass in the form of internal deposits and close spaced septa, but they may have been able to attain enough positive buoyancy to rise off the bottom before either becoming neutrally buoyant or settling down again. The ability to evacuate or flood as many chambers as possible would have decreased the time needed for such maneuvers. The ability to shift ballast or selectively add or reduce weight would have further facilitated their mobility.
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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.
==References==
==References==
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'''Credits'''
'''Credits'''
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[[user:John M|JM]]
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[[user:John M|JM]] revised 8-12-2012

Revision as of 15:38, 8 December 2012

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