Rayonnoceras

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The holotype, ''R solidiforme'' is discribed as having camerae completely filled with organic deposits (presumed to be calcite), although perhaps not necessarily all camerae, and a large siphuncle, solid throughout. If this truely represented the condition during the life of the animal it would have rendered it virtually immobile.  Any claim of an actively mobile nektonic preditor simply ignores the facts.  Not only is any rigid longiconic orthocone or cyrtocone difficult to meneuver in the first place, even when not overburdened with deposts, but the added weight provided by completely filled cameral and siphuncular spaces would have added great difficulty to any attempt of mobility.
The holotype, ''R solidiforme'' is discribed as having camerae completely filled with organic deposits (presumed to be calcite), although perhaps not necessarily all camerae, and a large siphuncle, solid throughout. If this truely represented the condition during the life of the animal it would have rendered it virtually immobile.  Any claim of an actively mobile nektonic preditor simply ignores the facts.  Not only is any rigid longiconic orthocone or cyrtocone difficult to meneuver in the first place, even when not overburdened with deposts, but the added weight provided by completely filled cameral and siphuncular spaces would have added great difficulty to any attempt of mobility.
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The heavy phagmocone and siphuncle, weighted by deposits secreted during the life of the animal, surely preclude any swimming mobility, especially in larger adults. While smaller juveniles may have had some "swimming" mobility above the substrate and the ability to move from place to place, actively hunt and escape predation, larger individuals probably spent most or all of their time in one place on the bottom, waiting in ambush for passing prey, much like modern wobegong or angelfish.  
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The heavy phagmocone and siphuncle, weighted by deposits secreted during the life of the animal, surely preclude any swimming mobility, especially in larger adults. While smaller juveniles may have had some "swimming" mobility above the substrate and the ability to move from place to place, to actively hunt and escape predation, larger individuals probably spent most or all of their time in one place on the bottom, waiting in ambush for passing prey, much like modern wobegong or angelfish.  
No comparison can be made between the heavy carbactinoceratids including ''Rayonnoceras''. tentitive pseudorthocerids, or the morphologically similar actinocerids, and the Middle and Upper Ordovician Endoceratidae, other than for having, sometimes large, straight shells. Endocerids are simply a very different critter with different and unique internal structures and undoubtedly different abilities and habits.  
No comparison can be made between the heavy carbactinoceratids including ''Rayonnoceras''. tentitive pseudorthocerids, or the morphologically similar actinocerids, and the Middle and Upper Ordovician Endoceratidae, other than for having, sometimes large, straight shells. Endocerids are simply a very different critter with different and unique internal structures and undoubtedly different abilities and habits.  

Revision as of 01:01, 13 December 2009

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