Giant ammonite

It seems I'm continuing on a molluscan theme...
This is a Giant Ammonite, Titanites giganteus, found in the Earth Hall of the Natural History Museum. Well, it was actually found in Dorset, but now resides in the NHM... It is 147 million year old (so it lived in the Jurassic period).
I love the nautiloids that are still around (like Nautilus), but 'though ammonites look rather like them, ammonites are actually more closely related to coleoids (including all the different types of squid & octopus).

Linguistic digression: do you know the plural of "octopus"?
Many people say octopuses, which seems a fair enough anglicisation; some people say octopi, which is cute, but incorrect (it would only be octopi if octopus was derived from Latin, so octopi is sort of pseudo-Latin...). The linguistically correct plural is octopodes (because octopus is derived from Greek)! I think octopodes is also the cutest one. The same goes for "platypus" too: the plural is platypodes.

I was just taken by the very geometric spiral of the fossilised shell. There is another ammonite fossil in the museum which shows the "logarithmic spiral" form much more dramatically (it expanded more as it grew); this one's radius does increase exponentially as it grows around, but much less dramatically.