Plectronocerids and other neat nautiloid fossils

Discussion in 'Cephalopod Fossils' started by willsquish, Jul 21, 2008.

  1. willsquish

    willsquish Blue Ring Supporter

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    Hello, I was researching plectronocerids, and came across a few mentions (copied mentions) of some specimens from New Mexico and Texas, but I can't find any in the literature. :read: Most seem to be Chinese. Does anyone know which plectronocerid(s) might be in North America and which formation? :confused: Thanks!

    Also, I went looking for ascocerids lately, and found a few. They're the ones with the deciduous juvenile stage. Nothing really perfectly complete, but a few with the juvenile stage still attached in the matrix. One of which confirms that at least for Billingsites, they only lost one stage. Some had proposed that the juveniles lost pieces as they went, and so had a rounded adapical tip. But the specimen I have seems to go to a point. The problem, I think, is that most people don't get them in the matrix, and steinkerns can break at the septa. :grad:

    I can post pictures soon. Gotta clean up and photograph first. :smile:
     
  2. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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  3. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Memoir 12 (below) has a nice summary of the Plectronocerids and all other early cephs. The Cambrian forms coming from the San Saba Formation of Texas. It would be well worth it to get a copy somehow. It is old, and Flowers classification may be way outdated (he insists that bactritids are not the ancestors of ammonoids, and was a firm believer that a "Canadian System" was between the Cambrian and Ordovician [however, it may be the Early Ordovician could still be called "Canadian"]).
     
  4. willsquish

    willsquish Blue Ring Supporter

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    Ascocerid

    Wow. That's excellent. Will definitely order a copy. I thought plectronoceras and palaeoceras sounded not very chinese. Still, texas is a good sized drive away. Will take some planning.

    As promised, though, attached are a few pictures. The first being a pretty good longitudinal cross section of Billingsites noquettensis, with the cone still attached. The second would be the entire cone (up to the point, but hard to see, though the vugs follow its progress back) and part of the adult section, though most of that's broken off. And the third is my only real evidence that they did indeed break off at all. The other ones I found all had parts of the cyrtocone still attached.
     
  5. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Thanks for posting these pics Willsquish, unfortunately being an old fart :old: I am having trouble seeing most of the fossil :sad:. I can see the chamber that is now a vug and I can make out a few septa on some of the other pics, but that is about all. Any chance of maybe a paint sketch showing at least the basic outline of the fossils?

    Here is a link to a drawing of Billingsites in case others cant see the shape.
     
  6. willsquish

    willsquish Blue Ring Supporter

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    Don't worry. The pictures don't really show many details unfortunately. I'm not sure how I can photograph it to make them easy to see, as it's not that easy to see up close. Often one needs to wet the surface to get beyond the bumps and chips. I suppose if I get some great equipment I could try slicing it.

    Here's a pic I amateurly touched up in paint with what lines I see using my hand lens and water, and what I see from different angles of shadow on the cyrtocone for some of those septa. I think I put the top of the shell a tad too high at the adoral part, but paint only lets you undo 3 times. So I just put the septa ending where the shell is there, more or less.

    Anyway, the one with the chamber vugs, part of the tube is in the part I chipped off it, and the line isn't fully seeable most of the places. I'll try to do that one next.

    For a good reference on this particular species, Billingsites noquettensis, you can check out Michigan's new deep blue program's copy of its description here:

    http://deepblue.lib.umich.edu/bitstream/2027.42/48352/2/ID195.pdf

    The 2 plates in the last few pages show not only the specimens collected, but one with a longitudinal slice, showing the internal septal structure. Deep Blue, I believe, is working on publishing all U of M publications, or at least journals, online, except maybe one or two. Great for many subjects.
     
  7. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    That helps considerably :notworth:

    Very interesting cephalopods, I will have to look into any new papers on these things to see how the plugging of the truncated portion of the conch is now theorized. The long "Argonaut" arms plugging the hole is interesting, and Flowers idea that the siphuncle is complex enough to deposit a plug also, I wonder if the adult shell was internal???

    That is the same reason most of my Ordovician cephalopods are just photos of naturally sectioned fossils
     
  8. willsquish

    willsquish Blue Ring Supporter

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    Yeah. It would seem most likely to be an outside shell, at least to me, since its closest ancestor was an oncocerid, which gave rise to the modern nautiloid. That, and on another specimen, with shell clearly in good condidtion, it's pretty thick protective shell (about a millimeter in thickness). I'd have to say I'm leaning on the interesting siphuncle work. It goes through a pretty severe turn in the first chamber, so maybe it pinches itself off.

    My only question is how did it get rid of the conch? It must have had to keep the last deciduous chamber (which looks pretty thin in comparison when you see the juvenile the paper has) in good working order til the end, and reabsorb at the edge. I half wish I'd found a cast off piece in matrix to look at its edge.

    It's funny though, you read papers on other ascocerids, and it's just such a sparse record, there's a lot of things each guy doesn't really know. For instance, on an ohio specimen (shuchertoceras I think?) they had no shell attached, but they'd found some deformed ones, so they hypothesized it had a very thin shell. Clearly not so much the case looking at its close relation here.

    Here's another specimen with the shell still partly there. It's hard to read the sutures again, though, especially because it appears to be broken diagonally. But the gas chambers seem more crystalized than the living chamber at least, so one knows which way is up.
     
  9. willsquish

    willsquish Blue Ring Supporter

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    ascocerids

    Here's my touchup of the vuggy one. Very hard to see the many of the sutures unfortunately. The rock in which all these were found is limestone, and so calcite structures, when exposed to weathering end up blending in perfectly. The dashed lines refer to what the probable outline is in the chipped off rock (which I have, and can see the oval section of the shell going in and out in). made a mistake on the shell early on, and penciled that out as best I could with the corrected line below it. The 2 vugs helped alot though, as well as one raised suture that weathered out that you can't see to well in this lighting, but in shadow stands out.
     
  10. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    I just saw the Animal Planet Walking with Sea Monsters with by Nigel Marvin done in documentary style. I had no idea that Orthocones (sp) were so large. For the uninitiated at least, the program seemed to do a good job at taking fossil data and making it come to life. Sometimes it was hard to remember that the action was not really taking place. The original was created in 2004 but PBS recently aired it and it may come on again if anyone else wants to see it.
     
  11. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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  12. willsquish

    willsquish Blue Ring Supporter

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    I love the second pic there. Interesting and not too easy to find group, the 'Intejocerids' .


    Yeah, I ended up using an exacto to remove a millimeter or so to get a faint remenant of the pre-weathered/assimilated shell on the other ascocerid, so I could reconstruct the other 2 septa. It's a weird shape, since the rock angles back mid way up.
     
  13. Nauti-guy

    Nauti-guy Cuttlefish Registered

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    Plectronocerids in New Mexico

    willsquish, I hope you were able to obtain, at least access to, the two references given by Architeuthoceras. Another good reference that covers more recent findings in China is that by Curt Teichert, 1988, Main Features of Cephalopod Evolution, Volume 12 Paleontolgy ad Neontology of Cephalopods, Clarke and Trueman Eds, in The Mollusca, Academic Press.

    Regarding plectronocerids in New Mexico, I believe there aren't any. The nearest are found in the Trempealeauan (U Camb.) San Saba Ls. in central Texas. The Lowest cephalopod bearing formation in New Mexico is the upper Gasconadian Sierrite Limestone of the El Paso Group. Cephalopods reported in the literature (Flower) include Ellesmeroceras, Clarkocers, and Ectenolites. The underlying Bliss formation is a near shore sandy deposit with some brachs and trilobites, but to my knowledge no cephalopods. The Bliss extends into the Lower Ordovican from the Cambrian, the boundary determined by graptolites.
     
  14. willsquish

    willsquish Blue Ring Supporter

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    plectronocerids

    Yep, I ordered the references and read through. When next I get a suitable vacation time, I'll try to get down to san saba. Back to school for now, though.
     
  15. vw1

    vw1 Cuttlefish Registered

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    Does it become clearer if the specimens are wet?
     
  16. willsquish

    willsquish Blue Ring Supporter

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    cambrian cephs

    Update. Yes here they are. Some plectronocerid, cambrian cephalopods.

    The one triangular larger one on the right, I believe, is a palaeoceras. The white portion is just over one inch in length. The rock and lichen did interesting effects that made these pop out a bit. The chambers clearly got more filled with calcite, which apparently these lichen don't like (liche?). And these are left uncovered. Other chambers closer to the end and the living chamber filled with the surrounding matrix and got more degraded and colonized. One can see a faint outline of the wall of the living chamber on the palaeoceras.

    The one somewhat large sliver of white, with a second sliver of white to the left of the palaeoceras along with the faint outline in the matrix there, I believe is a plectronoceras.

    There's a small sort of very small slender fellow below the one on the right, which may be a balkoceras, or one of the not-quite-cephalopods that also happened at the end of the cambrian. Ones with chambers but no siphuncle.


    Only cephalopod order left to find is intejocerida. Like Rossoceras Any suggestions?
     

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  17. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Nice fossils :smile: Can you see any signs of the septa, or are they too thin? Are there a few trilobite parts floating around on that rock, or are they brachiopods?

    In the Juab Formation around Fossil Mountain, in the Southern Confusion Range, Utah, Rossoceras is fairly common. 8-)
     
  18. willsquish

    willsquish Blue Ring Supporter

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    The septa are fairly faint on this, but when wet, they can be seen. In the pic you can see some very faint ones from shadows on the calcified portion, and from the shadows in the matrix. Another specimen which seems to have mostly balkoceras has more visible septae. There are some gastropod curls in this rock, as well as some brachiopods. There is at least a pygidium I see on the block I've not photographed yet which has primarily balkoceras (and/or possibly kygmaeoceras, still working it out). And some other trilobite bits on rocks from the same location as this piece, a bit lower down.

    Rossoceras is common? Know anyone who might trade? The road trips, while fun and adventurous, take awhile to save up time to go on, with research as it is.
     
  19. willsquish

    willsquish Blue Ring Supporter

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    But yeah, you need to click on the photo then click it again, so you can get it to 100% magnification.
     
  20. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    OK, I can finally see a few, they are faint. :oops:

    I'll see what I can do. :wink:
     

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