AndyS;84713 said:but I insist to be quoted completely since there is more of it :
All the best,
Sorry Andy, I will quote completely in the future
Phil;84718 said:I wonder if hermits switched from ammonites to gastropods or whether they used both kind of shells throughout their evolutionary history. I have always thought they were opportunists using whichever shells for shelter that came along, but maybe they are species specific in their choice of shells? I really don't know. I'm sure a decaying ammonite would have made a good meal for such a roving scavenger.
cuttlegirl;84724 said:More questions... Since an ammonite shell had chambers, would an ammonite shell be lighter than a gastropod shell of the same size? It seems that an ammonite shell would cost less energy to haul around and still provide protection for the hermit crab.
Do any animals inhabit empty Nautilus shells today? Or do they float? Did ammonite shells float after the animal died? If so, then how did a hermit crab inhabit it?
It seems to me that if a crab got into a floating shell it would float away. I can just imagine a crab getting into an ammonite shell that washed up on the beach, as the tide comes in it starts to float, the crab has to hurry and find a new shell, preferably a gastropod shell that doesnt float.
Ammonite shells did float, that is why they make such great index fossils, they scattered on the current, at least that is the old way of thinking. It seems Nautilus shells dont fall far from the tree though, at least not worldwide. Ammonite shells were very thin and delicate (some think that is why the sutures were so intricate, to strengthen the shell) so they probably broke or became waterlogged very easily and were available for crabs to inhabit on the sea floor. The ammonite in the link AndyS provided seems to have shell damage, allthough I cant tell if the damage occured before or after the crab inhabited the shell or even if the damage occured before or after fossilization. So I think that crabs would only get into shells that were either broken or waterlogged, and not the ones that were still floating.
From the pics below it would seem that crabs have some prefered shell shapes so some may have evolved to occupy certain ammonite shells, that one in the article seems to fit like a glove.
And my ammonites are very exciting floating along the shelf, or on the desk, I could sit and watch them all day!