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nautiloid(?) I bought at a fossil shop

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Here are two blurry pictures fo a nautiloid fossil from Tajikistan. I'll try again someday when my hands are steady.

Too-much-coffee Melissa
 

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I have to echo Monty's laudatory post about our fossil fiends. Much as I have admired rocks in the past, I would never have noticed this without the education I've received from TONMOers, especially Phil, who made the fossils in the British Museum palpably relevant rather than simply history.
 

Architeuthoceras

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Nice fossil Melissa, I believe it is an ammonite, just going by the expansion rate of the shell and the radial orientation of the septa (a simple septa cut in half would be crescentric).
 

monty

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Architeuthoceras;104325 said:
Nice fossil Melissa, I believe it is an ammonite, just going by the expansion rate of the shell and the radial orientation of the septa (a simple septa cut in half would be crescentric).

My first thought was "that has a very long body chamber, so it's probably an ammonite"-- in the spirit of learning from the fossil fiends: is that a good reaction, or just me showing my ignorance? (I didn't think about either of the criteria you did mention, Kevin, although that may have been part of my "that looks like an ammonite, but I'm not sure why" that preceded my "maybe 'cause of the long body chamber" thought.)
 

Architeuthoceras

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monty;104326 said:
My first thought was "that has a very long body chamber, so it's probably an ammonite"-- in the spirit of learning from the fossil fiends: is that a good reaction, or just me showing my ignorance? (I didn't think about either of the criteria you did mention, Kevin, although that may have been part of my "that looks like an ammonite, but I'm not sure why" that preceded my "maybe 'cause of the long body chamber" thought.)

The long body chamber is another sign that it is probably an ammonite, maybe that is why I notice the expansion rate, coiled nautiloids seem to have only a few whorls and a short (relatively) body chamber while ammonoids have many whorls with a long body chamber, there are always exceptions. The siphuncle also seems to be ventral which is another mark of ammonoids (if that is the siphuncle I see) of coarse there are always exceptions. The real test would be seeing prochoanitic septal necks on the siphuncle, but again, there are exceptions there too.

One of the fossil fiends :sagrin: being fiendish :wink:
 

monty

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thank you, my good fiend!
 
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Literal dumb luck! I called it an ammonite in the shop because I knew it wasn't a belemnite, and I don't know any more than that.:earlyammo:argonaut::ceratite::goniatite:nautilus::plectrono:bactritin:earlynaut
Everything I know, I learned from the smileys. Thanks, Phil!
 

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