Hermit Crabs in Ammonite Shells


Dec 31, 2006
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:
PS:Yeah- nautilus shells can float pretty far. I bet you could even use them to map currents sometimes ^_^


Staff member
Moderator (Staff)
Nov 19, 2002
: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: