Triradial constrictions, why?

[POD-L]

Excellent specimens!!Thanks for posting them Hajar

 

[DWhatley]

You get the most interesting stuff. How's the live version of your collection thought coming?

 

[Hajar]

There are no live cephalopods in this house at the moment though a freshwater tank is up and running again.

I still find these odd clymeniids very strange - I can't even see an aperture on them. Here's a paper about them: http://www.schweizerbart.de/resources/downloads/paper_previews/59079.pdf

 

[DWhatley]

I can't even see an aperture on them.

Maybe my artistic liberty with my signature titanites is not so imaginary for another species?

 

[Hajar]

It looks like the symbol for an ancient mystical society.

 

[DWhatley]

Earliest Japanese puzzle box?

 

[peftypefty]

Let us not forget the diaboloceratids of the Pennsylvanian:

Diaboloceras - Google Suche

I think there is a lot more to this triangularity than the constrictions alone. I would bet that the growth lines on any of these forms would (if preserved) indicate saltatory life-position, i.e., staying in one shell orientation in the water for months, then rapidly rotating to the next shell orientation ("rounding the corner").