aek Posted December 6, 2017 Share Posted December 6, 2017 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. Link to comment Share on other sites More sharing options...
JohnBrewer Posted December 6, 2017 Share Posted December 6, 2017 @TqB amongst others may know. John Map of UK fossil sites Link to comment Share on other sites More sharing options...
TqB Posted December 6, 2017 Share Posted December 6, 2017 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. 3 Tarquin Link to comment Share on other sites More sharing options...
Manticocerasman Posted December 6, 2017 Share Posted December 6, 2017 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. growing old is mandatory but growing up is optional. Link to comment Share on other sites More sharing options...
TqB Posted December 6, 2017 Share Posted December 6, 2017 It applies to nautiloids as well (and ammonites). Tarquin Link to comment Share on other sites More sharing options...
aek Posted December 6, 2017 Author Share Posted December 6, 2017 Thanks! @TqB @Manticocerasman Link to comment Share on other sites More sharing options...
PFOOLEY Posted December 7, 2017 Share Posted December 7, 2017 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... ...and yes, the septa before the living chamber (red arrow) are spaced more closely. "I am glad I shall never be young without wild country to be young in. Of what avail are forty freedoms without a blank spot on the map?" ~Aldo Leopold (1887-1948) New Mexico Museum of Natural History Bulletins Link to comment Share on other sites More sharing options...
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