Plectronocerids and other neat nautiloid fossils

willsquish

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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:
 

Architeuthoceras

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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 It is old, and Flowers classification may be way outdated (he insists that bactritids are not the ancestors of ammonoids, and was a firm believer that a "Canadian System" was between the Cambrian and Ordovician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"]).
 

willsquish

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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.
 

Architeuthoceras

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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.
 

willsquish

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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.
 

Architeuthoceras

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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???

willsquish;122088 said:
I suppose if I get some great equipment I could try slicing it.
That is the same reason most of my Ordovician cephalopods are just photos of naturally sectioned fossils
 

willsquish

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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.
 

willsquish

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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.
 

DWhatley

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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.
 

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