Preserved (?) ammonite chambers

[Architeuthoceras]

I found this the other day, Metoicoceras geslinianum, 130mm dia., a Late Cenomanian (Late Cretaceous) ammonite. The septa are probably replaced with calcite but there is no sediment infill of the camerae except for the last few, the inner phragmocone was complete before I found it. It was in a shattered concretion, I was real lucky to collect as much as I did.

 

[Architeuthoceras]

A couple of closeups of the chambers. The last one is the inner whorls of the phragmocone.

 

[spartacus]

Nice one Kevin, beaten up ammonites like that are a great for demonstrating how these things are put together, something you can't do with a perfect shiney one !

Keef

 

[Architeuthoceras]

I'll be dag nabbed if I can find any septal necks, must be very very small.

 

[spartacus]

I take it you know where to look. Phil knows loads about ammonites if you're unsure !

Keef

 

[Phil]

Sorry for the delay in replying, I've been away for two weekends running and have barely been online. I'm still recovering from the Saturday's Beer Festival in Belgium...

Nice find Kevin. Metoicoceras is pretty odd looking with a tiny umbilicus. Does this species have any siphonal tubercles? Here in southern England Metoicoceras geslinianum is not uncommon in the Upper Cenomanian chalk, not that I've ever seen one unfortunately. As a mini-factoid Metoicoceras is one of these ammonites that displays sexual dimorphism with the male often being half the size of the female but much more heavily ornamented. Is this a macroconch?

I take it you know where to look. Phil knows loads about ammonites if you're unsure !

Keef

You kidding me Keef? I'm just a moderator with a couple of good books, not an expert! (to paraphrase Dr Bones McCoy). Believe me, I defer to Kevin in all matters!

 

[Architeuthoceras]

It has ventro-lateral clavi on the inner whorls, the venter is slightly concave, then rounded with low nodes. I am quite sure it is a macroconch.

I found the septal neck, way down the bottom of the ventral lobe. I had to point the light down just right to get this pic. The venter is at the bottom and the view is looking adapical. The neck is coming out toward the aperture (prochoanitic), recrystalized, but thats it.

 

[spartacus]

I've been away for two weekends running !

streuth Phil you must be fit as ! had you down as a real ale swilling, couch spud , turns out your fridge is full of yoghurt & steroids !

Good job hunting down that pesky septal neck Big Kevin

Keef