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Ordovician Coiled Nautiloid

Architeuthoceras

Architeuthis
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Found this the other day. Quite remarkable preservation for something almost 500my old. All the shell is missing, an external mold on the left shows how the shell had small ribs or undulations, and the growth lines are visible. The siphuncle, or at least an internal mold of the siphuncle is seen near the top of the photo. Some of the internal molds of the chambers have been silicified and show how closely spaced the septa were. There is also a gastropod internal and external mold just above the nautiloid.
 

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Phil

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That's fantastic Kevin.

Any idea what sort of nautiloid it is?
 

Architeuthoceras

Architeuthis
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Not near as nice as a chunnel nautiloid is it :frown: Probably Aphetoceras like the other one, but it may be just a partially coiled form, too bad it isnt all there.
 

Phil

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Maybe not as nice, maybe, but it is five times older....

If anyone is wondering what Aphetoceras looked like, here's a little image. I believe that this type of shell is known as a gyrocone (?).
 

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sorry I'm late big Kev, was unavailable at the time of posting & still catching up.
that's pretty special considering what the remains could have gone through after 500my wow :shock:

not quite so impressive but similar was a pair of [/i]Cardioceras chalcedonicumsssss (possibly) I found in a nodule in the UK. A bit fragged, but like Steve Austin, I will rebuild them (on a tighter budget)
when i started getting all the bits together it was amazing what I found I had considering it was up to 160myo. having read up & been educated by you guys on what's what it was pukkal to see how our curly friends were really put together other than by a diagram

hats off :notworth:
I will post as soon as I find their box, now where'd I put 'em ?

Keef
 

Architeuthoceras

Architeuthis
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I just attached a larger photo for a little more detail on the first post. And added this photo from another thread.


With the whorl and spiral expansion rates on this I am quite sure it is an Aphetoceras sp. This means it was the first nautiloid that coiled more than 1.25 whorls, and makes it the first member of the Order Tarphyceratida, the ancestral order of all coiled nautiloids*. Those that didnt coil more than 1.25 whorls, and have the large, ventral siphuncle, and close spaced septa, are left in the order Ellesmeroceratida, the order all the other forms of cephalopoda sprang from.
It is amazing what you can learn when you go to the library instead of the desert. :cool2:

* this depends on who's classification you are reading.
 

Phil

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Thanks Kevin, a lovely and interesting find. Is this a rare specimen, the first such you have found?

(By the way, I've restored the line drawing above for everyone to see a reconstruction of the shell form)
 

Architeuthoceras

Architeuthis
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These two are the only ones I would confidently refer to Aphetoceras. there are a few external molds in the same horizon that have the same ornamentation, but I cant be sure they are the same genus.

This small impression maybe an external mold?? compare it with the external mold (lower left) on the first attachment.
 

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