Triassic Coleoids

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Mar 7, 2009
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Does anybody know anything about Triassic coleoids such as the attached Atractites? There are two in the slab, the larger being 95 mm long. At the top is a chambered orthocone (Michelinoceras). These are from the Middle Triassic Prida Formation of Nevada.

From the outside they look like belemnites, but I polished a partial specimen and see that it is totally recrystallized (originally aragonite?).
 

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No sign of a chambered phragmocone, but as you can see in the attached roughly polished long and transverse sections there has been extensive recrystallization.
 

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The link doesn't seem to work. The paper is: Atractites guards from the Early Jurassic of New Zealand, A. B. Challinor, Department of Earth Sciences, University of Waikato, Hamilton, New Zealand. Online publication date: 30 March 2010.

"Guards extensively recrystallised, composed of interlocking calcite crystals. Concentric lamellar and poorly defined radial structures remain visible on unprepared transverse surfaces and are faintly visible on a polished transverse section."
"No remnant of the phragmocone is preserved."
"The crushed nature of C1384 may indicate that the guard was poorly calcified in life, perhaps partly or largely organic (Jeletzky 1966), although some authors suggest it was aragonitic (Doyle 1990).."
 
Could you post a link to the inaccessible papers you'd like to see? I too have been wondering at the difference between aulacocerids and belemnitids and I have university access to many literature sources for now.
 
I think Hajar linked to most of the papers I saw on a search. I did read a paper recently that removed Hematites from the Aulocoerida, I'll try to remember where I read that... An updated treatise like article would sure help with classification of these Coleoids. :confused:
 

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