Hermit Crabs in Ammonite Shells

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 :oops:

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. :lol:
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!:wink:
Hallucigenia mentioned a Stephen J. Gould article about hermit crabs in an AIM conversation, which I was trying to google for, and found this article on a hermit crab housing crisis instead. That notwithstanding, the Gould article seems rather relevant... google suggests it's probably "GOULD, S. J. (1978a): Nature's odd couples. - Natural History, 87(1): 38-41. New York." reprinted in The Panda's Thumb, but I don't have that one... The quick "I haven't read it" version (perhaps Hallucigenia can fill in more) is that there is some island somewhere where there is a species of hermit crabs that only live in the shells of an extinct gastropod, so there's no source of new shells for the crabs, and they're stuck in an "evolve or die" situation because they depend on another species that isn't around any more... much like the ammonite inhabitants... Cool biology, but sad story...
Holy shit, that link is amazing. But yeah, that's the right Gould reference you've tracked down; I went today and found it as well, and that's definitely it in The Panda's Thumb. You've told the story right, in a nutshell -- I think the island in question was probably in the Bahamas, somewhere around Gould's research area. Reminds me of Terry Pratchett's hermit elephants (they live in abandoned huts).

Floating shells...yeah, that would seem to be an issue, especially for hermits that spent lots of time underwater (there are some, I think, that are primarily terrestrial). In fact, when I was reading this a moment ago, my first thought was "Maybe they drilled holes in some of the chambers?", but on examination of the photos, I don't see any obvious damage to the shells...anyone know more?
monty;84744 said:

Fantastic!! a couple million years from now some paleontologist will come upon a bed full of little plastic houses, with "Microsoft" or "DuPont" printed on the top, and wonder why hermit crabs preferred one or the other. :lol:

Maybe a floating shell was desirable, especially if the crabs had found a way to maneuver around with it.
ammonite stuff

About the ammonite sutures- the hypothesis put forward by Rev. William Buckland (I think he was the first one, though not sure) was that the sutures in ammonites became more complex over time because it helped overcome hydrostatic pressure so that the animals could hunt in deep waters. However, there has been a lot of re-analysis of that theory recently. Some people think now that the sutures are complex because that let the ammonite attach its muscles more easily to the shell wall. Computer simulations of the stress-levels on shells indicate that the one with the simplest septal sutures are actually the _most_ resistant to pressure. Nautilus shells are pretty thick and their sutures are much less complicated than the ones of the later ammonites. They survive at some quite impressive depths underwater. W.B Saunders and others believe that the ammonites were actually shallow-water organisms, and the suture complexity didn't have anything to do with structural support. This is one of the papers written on the subject, but there are a lot of others:
The Ammonoid Suture Problem: Relationships Between Shell and Septum Thickness and Suture Complexity in Paleozoic Ammonoids on JSTOR
PS:Yeah- nautilus shells can float pretty far. I bet you could even use them to map currents sometimes ^_^
:welcome: kraken, and thanks for the link.

I think there is also the idea that the ammonoids made more complex sutures just to make up for the thinness of their shell.

From my limited experience, ammonoid and nautiloid shells in the same beds seem to have about the same preservation, and damage if any. For example the inner whorls of Eutrephoceras, a coiled nautiloid, and Placenticeras, an ammonoid, are both usually flattened and poorly preserved while the living chambers are fairly intact, assuming sediment pressure was not alot different than water pressure.:wink:

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