Michelinoceratida

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The Michelinoceratida  is a Lower Ordovician (Cassinian) to Upper Triassic assemblage of orthoconic and cyrtoconic nautiloid cephalopods that includes both orthoconic and cyrtoconic forms with varied ontogeneses, lending to the idea this group may be polyphyletic. Systematics are particularly subject to revision, with recent authors suggesting that some families (particularly the Pseudorthoceratidae) should be removed.  
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The Michelinoceratida  is a Lower Ordovician (Cassinian) to Upper Triassic assemblage of orthoconic and cyrtoconic nautiloid cephalopods with varied ontogeneses, lending to the idea this group may be polyphyletic. Systematics are particularly subject to revision, with recent authors suggesting that some families (particularly the Pseudorthoceratidae) should be removed.  
'''Characters''' (from Sweet 1964): Conchs straight to curved (never coiled), smooth or elaborately ornamented; cameral deposits typically well developed; siphuncles with orthochoanitic or secondarily cyrtochoanitic septal necks and thin connecting rings, empty or occupied by parietal or annulosiphonate deposits.
'''Characters''' (from Sweet 1964): Conchs straight to curved (never coiled), smooth or elaborately ornamented; cameral deposits typically well developed; siphuncles with orthochoanitic or secondarily cyrtochoanitic septal necks and thin connecting rings, empty or occupied by parietal or annulosiphonate deposits.

Revision as of 01:36, 24 May 2012

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