Ammonoid Chamber Formation

Discussion in 'Cephalopod Fossils' started by cuttlegirl, Feb 22, 2009.

  1. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    I have a hard enough time comprehending how Nautilus can form concave septa - how did Ammonites form and replicate such complex ones?
     
  2. Phil

    Phil Colossal Squid Supporter Registered

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    Good question there Cuttlegirl. I've no idea of the correct answer but I guess there must have been a slow selective pressure for increasingly complex suture patterns amongst the ammonoids. What practical function increasingly complex sutures may have served is totally obscure to me - I doubt if they would have afforded tougher shells as the modern Nautilus has very simple curved sutures and they can attain considerable depth. There must have been some sort of evolutionary advantage for the evolution of complex sutures and simpler ammonoid forms to fall by the wayside.
     
  3. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Seems that after every mass extinction the complexity of sutures increased. I dont know if it was because only those with more complex sutures survived or some other reason. In the figure below you can see the different sutural forms. The Agoniatitic form basically disappeared after the end Devonian extinction, The Goniatitic, after the end Permian, and the Ceratitic after the end Triassic. And of course the Ammonitic was replaced by the Orthoceratitic after the extinction of the ammonoids after the K/T (end Cretaceous) event.
    [​IMG]

    It was nice to get out in the field again after the long cold winter. :grin:

    A very nice new avatar you have there Phil.
     
  4. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    As I understand it (and I am quite possible wrong...), Nautilus attach with muscles to the sides of the last chamber and have a membrane covering the last septum. When it is time to create a new septum, the animal somehow pulls forward and starts secreting a new septum. I can see how the animal could replicate a simple concave form, but how did ammonites continue to replicate the same complex septa throughout their lifetime? Was their mantle/membrane stiff (kind of like a silicon mold) or did they pull off the last septum a little bit at a time, reattach, start secreting the new septum and then pull forward the rest of the parts?

    Anyone have access to Lethaia? http://www3.interscience.wiley.com/journal/119205295/abstract

     
  5. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Another paper on "Cameral Membranes", I'll see if I can get copies of these.


    Cameral membranes in prolecanitid and goniatitid ammonoids from the Permian Arcturus Formation, Nevada, USA

    Neil H. Landman; Kristin Polizzotto; Royal H. Mapes; Kazushige Tanabe
    DOI: 10.1080/00241160601008395
    Lethaia, Volume 39, Issue 4 December 2006 , pages 365 - 379


    Abstract

    We describe cameral membranes in prolecanitid and goniatitid ammonoids from the Lower Permian Arcturus Formation, Nevada, USA. The membranes are preserved as phosphatic sheets and were originally composed of organic material such as conchiolin. Because the phragmocones are filled with micritic calcite, the cameral membranes can be exposed by etching with weak acetic acid. The membranes are associated with the siphuncle and also coat the septal faces and chamber walls. The siphuncular membranes are much more extensive in the prolecanitids than in the goniatites. These membranes appear in the prolecanitids at the beginning of the third whorl, corresponding to a shell diameter of 3-4 mm, and become more complex through ontogeny. Additional membranes, called transverse membranes, appear in some of the septal saddles on the ventrolateral side. The siphuncular membranes in prolecanitids are very similar to those in the Ceratitina plus Mesozoic Ammonoidea, suggesting that such membranes are widely distributed in this group. However, the origin and function of these membranes are unclear. We argue that the siphuncular membranes were sequentially secreted by the rear mantle during forward movement of the body and were not produced by desiccation of cameral liquid after the formation of the chambers. The most compelling arguments for this interpretation are the abrupt appearance of these membranes at a shell diameter of approximately 3-4 mm in prolecanitids, ceratites, and ammonitids, coincident with the end of the neanic stage, and the uniform increase in complexity of the membranes through ontogeny. The shape of the siphuncular membranes in prolecanitids suggests the presence of an invagination on the dorsal side of the siphuncle during part of the chamber formation cycle. Cameral membranes may have served a variety of functions including stabilizing the cameral liquid to reduce rocking motion during swimming, anchoring the siphuncle to the chamber wall, and facilitating cameral liquid removal, permitting a faster rate of growth.


    Keywords: Ammonoid chamber formation; cameral membranes; goniatites; Permian; prolecanitids
     
  6. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    If I were to win the cephalopod lottery (besides wanting to see a live Meso or Archi...), I would love to spend a day (or maybe a week) talking to Neil Landman.
     
  7. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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  8. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Again, I have moved some posts into a new thread to keep all posts about ammonoid chamber formation together in a seperate thread. Hope nobody minds.

    a picture of the fossil that started it below.
     

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  9. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    From Ammonoid Paleobiology, Chapter 9, Morphogenesis of the Septum in Ammonoids, Checa and Garcia-Ruiz, pg. 253-296. (incomplete google book preview) Alot of stuff about viscous fingering, fractals, pseudo-sutures, and Saffman-Taylor instability. I,m still digesting, and I think it is still not completely understood by those who think about it harder than I have the last few days.:bugout:
     
  10. Nauti-guy

    Nauti-guy Cuttlefish Registered

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    another idea

    Neither Landman et als' 2006 paper nor Antonio Checa's article on cameral sheets seem to really explain the complex suture formation in ammonoids, at least not in the abstracts. Both abstracts explain biological processes that seem to have taken place, but not fully the manner in which septal crenulations were made. I suspect the formation of convex forward ( adoral) septa, complex sutures, and forward poining (prosiphonitic) septal necks are related and that the nature of the inracameral membranes is a result of the process not the cause.
    As a working hypotheses, when the animal inched forward to create a new chamber, the back end of the mantle was drawn muscularly in so as to be concave, unlike the back end of nautiloids which is and was left bluged out convexly. In ammonoids this would continue to draw the central region of the septa and the septal necks forward. The complexity of saddles and lobes may result from a sort of puckering as the back side of the mantle was drawn in. The cameral membrains were formed during this process inorder to facilitate cameral desiccation. Anyway, take it for what it's worth.
    The reason for this aspect of ammonoid biology is unknown and I doubt it was of any advantage, after all the simpler nautilods have persisted to the present. On the other hand this character found in ammonoids, once established, held on for the millions of years from the middle of the Paleozoic until their end in the late Cretaceous.

    So much for speculative science

    Nauti-guy
     
  11. monty

    monty Colossal Squid Staff Member Supporter

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    If it were just "puckering" wouldn't it be more random, and less prone to being so regular that it can be used for species identification? I've always assumed the complexities had to be under direct control of the animal, somehow. I'd also expect that if it weren't rigidly controlled, it would vary a lot both around the suture and from chamber to chamber.

    :twocents:
     
  12. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    The adoral face of the septum of Prionocyclus macombi, the saddles are coming toward the viewer, they would have the rounded form on ceratites and all the small flutes on ammonitic sutures. The same view on a nautilus would be concave, like looking into a bowl.

    Just to help visualize the complete shape of an ammonoid septum, it would replicate this shape for every new chamber.

    Ventral view, adoral is to the left
     
  13. Nauti-guy

    Nauti-guy Cuttlefish Registered

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    Puckering?

    Point well taken, Monty. Perhaps the term as I envsion it is misleading. I am merely speculating that the sutural complexity and forwarly convex septa have a related cause which has to do with the mantle being drawm in. I agree this must involve to consistant organic control inorder to maintain the given pattern. Just what, I don't know.

    Someday someone undoubtedly will give us the real answer


    cheers

    Nauti-gut
     
  14. Pr0teusUnbound

    Pr0teusUnbound GPO Registered

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    funny, i was just doing a bit of research on this question.

    so far the one thing ive concluded is that ammonite must have had the most complicated backsides in the animal kingdom.
     
  15. Tentacle Toast

    Tentacle Toast GPO Supporter Registered

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    ...outside of Hollywood, anyway...
     
  16. Pr0teusUnbound

    Pr0teusUnbound GPO Registered

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    ive been working on visualizing ammonoid gas chambers for some time. these drawings should give you an idea how the chambers were shaped:


     

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  17. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Nice drawings!
     
  18. Pr0teusUnbound

    Pr0teusUnbound GPO Registered

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    why thank you! :coffee:
    among other projects im working on drawing ammonoid septal walls and gas chamber architecture base on suture line diagrams. the process takes a lot of time, concentration and research, but i plan on posting the results.

    ...oh, and my apologies if i diverted from the topic of this thread:oops:
     

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