Actinocerida

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m (Origin and Range)
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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) [[Protactincerida]] 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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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)
== Siphuncle Details ==
== Siphuncle Details ==

Revision as of 18:39, 25 April 2012

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