Triassic Coleoids

Discussion in 'Cephalopod Fossils' started by Hajar, Nov 18, 2010.

  1. Hajar

    Hajar Haliphron Atlanticus Registered

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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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  2. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Nice fossils, any sign of a phragmocone? Sorry, no info here, a few things on the web but not accessible to me. :roll:
     
  3. Hajar

    Hajar Haliphron Atlanticus Registered

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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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  4. Hajar

    Hajar Haliphron Atlanticus Registered

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    This describes a very similar style of preservation.
     
  5. Hajar

    Hajar Haliphron Atlanticus Registered

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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).."
     
  6. Hajar

    Hajar Haliphron Atlanticus Registered

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    This shows some partial phragmocones of Atractites.
     
  7. Hajar

    Hajar Haliphron Atlanticus Registered

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    and this shows more complete material.

    The only other aulacocerid I've seen was the Aulacoceras from Al Aquil on the Arabian ammonite thread. I'll go looking for more over the next couple of months.
     
  8. willsquish

    willsquish Blue Ring Supporter

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    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.
     
  9. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    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:
     
  10. Hajar

    Hajar Haliphron Atlanticus Registered

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    Many thanks willsquish. One paper I would very much like to see is related to the Michelinoceras in that specimen, rather than the Atractites and that's Mehl 1984.

    Was this your paper on Hematites Kevin?
     
  11. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    That wasn't the one I read, that is even better, that answers many questions. :notworth::notworth:
     
  12. Hajar

    Hajar Haliphron Atlanticus Registered

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    Aulacoceras

    This Aulacoceras, 13.5 cm long from the Triassic of Timor is quite impressive.
     

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    Terri likes this.
  13. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Beautiful fossil! Looks just like one of my (much smaller) Hematites. 8-)
     
  14. Hajar

    Hajar Haliphron Atlanticus Registered

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    Yes, they do look a lot like both the older Hematites and also the much younger Vasseuria. What do you think the grooves and ridges were for?
     
  15. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Being some of the first Belemnoids, I imagine it is just an experiment in how to build a solid rostrum. :wink:
     
  16. Hajar

    Hajar Haliphron Atlanticus Registered

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    Some details of another one of these.
     

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  17. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    These look alot like the endosiphocone of Ordovician Intejocerids, perhaps they are formed in a similar fashion. ???
     
  18. Hajar

    Hajar Haliphron Atlanticus Registered

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    Interesting; I've never seen one of those. Do you have a photo?

    Here attached is a photo revealing part of the "inner orthocone" of a broken Aulacoceras.
     

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  19. Pr0teusUnbound

    Pr0teusUnbound GPO Registered

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