nautiloid

I'm hoping someone who knows a lot about the evolution of the Nautilus will help me with this question. So as far as I'm aware, the ancestral number for all cephalopod limbs is ten and nautiloids had gained more (up to ninety). The thing I'm wondering is how and why, mainly the how part. Did the...

I just thought I would post some nautiloid cephalopod fossils from the mid Devonian Gravel Point Formation of Bay View, Michigan, USA. Found them years ago but was busy trying to find fish fossils.