Ammonites with carved/open end chambers?

[kingcobb]

I have seen Ammos like this for sale but wasn't certain what the work on the end was about and wasn't certain if it was accurate or what not.

 

Saw this pic on what I understand from here to be a very respected dealer's page and got curious.

 

What is the point of the carving/opening at end of the chamber?  Is it simply aesthetic or is it an accurate portrayal of the shell originally? 

[Tidgy's Dad]

This is erosion or breakage along the ammonite septum edge, the suture, the complicated folds of the chamber wall where it joins the outer shell. 

(edited.)

[grandpa]

As ammonites grow they add new living chambers to accommodate their growth in size.  These chambers are separated by "sutures".  The shape of the suture is a definitive ID for the species of ammonite.  What you have here is an ammonite that is not totally complete, very normal in finds of this fossil.  The jagged design you see is the suture pattern separating the chambers.  (The final living chamber is not there or it would look smooth as it grows to its final stage.)  That design can be used to ID the species.  This looks like a very nice ammonite.

[kingcobb]

Interesting...so when the seller lists this as a "whole ammonite" that is not technically correct?

[grandpa]

Correct.  It could have been 2X, 5X, 10x, . . . bigger than what you see.

[doushantuo]

 

inouclassic2017NEWESTcephalopostedsuturesrep33689.pdf

Suture pattern formation in ammonites and the unknown rear mantle structure

Shinya Inoue & Shigeru Kondo

Nature

Scientific Reports | 6:33689 | DOI: 10.1038/srep33689

HEAVILY RECOMMENDED READING

[aplomado]

I'm pretty sure some preparers intentionally carve out the sutures like this for style.