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aek

I'm curious how one can determine whether a cephalopod fossil is an adult or juvenile? I seem to recall hearing from somewhere that if there is a double suture line in the middle of the phragmocone indicates it is an adult.

 

Here are three Beloitoceras specimens I found at different localities. The specimen in the middle has double suture rings. Thanks for any insight.

 

IMG_1982.thumb.jpg.00c0c723b31f2ed69a73b7103630ba6e.jpg

 

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JohnBrewer

@TqB amongst others may know. 

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TqB

Basically true, the last two or three septa before the living chamber are more closely spaced at maturity.

It can also be pathological in earlier parts of the phragmocone, so if only one specimen that's the same size as others shows it that's another possibility.

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Manticocerasman

It depends on the kind of cephalopod I think.

For goniatites you can determine that it is an adult when you see that distance between the last suture lines are closer to eachother than the previous ones.

this is a similar situation as on the cephalopod on your picture. But I am not sure this is the case for all the cephalopods.

 

 

 

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TqB

It applies to nautiloids as well (and ammonites).

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PFOOLEY

Interesting topic (and one I must read more about ^_^)...I will have to look at more of my ammonites for this feature.

 

For reference sake, here is a mature specimen of the Upper Cretaceous Acanthocerid Ammonite, Spathites puercoensis...

 

5a2932d3697c3_Spathitespuercoensisadult.thumb.jpg.3bc7c615ef36031f7a1248aa6b1f04cd.jpg

 

...and yes, the septa before the living chamber (red arrow) are spaced more closely. 

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