Contrasting ammonites on one wall in London

[xxxVCxxx]

Hello everyone, 

I've come across a few ammonites on a wall in Central London and I'm just curious about them. The Ammonite on the left (or top one) has several chambers that appears to be full of rock coloured material. I know it isn't and I've wondered what it actually is. I know that chambers were filled with gas or fluid to help with buoyancy when the ammonite was alive, but how come it's been filled in since, and with what? Could anyone please explain this. 

Also, the right fossil (or bottom one) seems to have an amber coloured spot on the top right side. Could somebody describe this for me too please? 

 

Thank you.

xxxVCxxx

 

Right Fossil

 

Left Fossil

[xxxVCxxx]

Ooops - it's 3.45am here in the UK. The labels for the images are the wrong way around. 

[A.C.]

Happy to be corrected if I am wrong but from my understanding:

 

You are absolutely correct in life these chambers would have been capable of storing gasses to help with buoyancy similar to that of a fish’s swim bladder. Upon death though the ammonite would have settled to the ocean floor, maybe been buried with sediment (mud, sand, etc) perhaps as the body of the ammonite decayed some of that sediment filled the gaps (there would be at minimum a small hole for the siphuncle, which is part of the ammonite allowing for removing of water in the chambers to have access to the chambers) another possibility is similar to how geodes form some minerals were able to seep in and collect in these hollow areas of the shell. 
 

The different colors you see could have to do with different sediments, different minerals, etc.

 

Great finds!