Lorney Posted September 22, 2021 Share Posted September 22, 2021 I was out walking the river the other day and found this piece of an ammonite. It appears to be the inner whorl. The middle was filled in with rock hard sediment so I removed it. It also appears to be agatized. The whorl appears to be somewhat offset from side to side. My question is, do ammonites usually have each side of the whorl straight across from each other or are they offset a little bit? I have added a few pictures but you may not be able to see the difference from one side to the other. Link to comment Share on other sites More sharing options...
Crusty_Crab Posted September 22, 2021 Share Posted September 22, 2021 Answering your question, do ammonites have symmetrical whorls? Yes, in life, unless there is some strange pathology. Also, during the Cretaceous, they started evolving in variable shapes, where the spiral became unraveled, but they seem to have kept their bilateral symmetry. Can fossils be distorted so that they are not symmetrical? Yes, that is common and many papers have been published on the subject, search taphonomic deformation. Based on your pictures, I only see a spiral shaped impression in picture 3, which does not have enough detail for me to even conclude if it is an ammonite, a gastropod or something else. 1 Link to comment Share on other sites More sharing options...
jpc Posted September 22, 2021 Share Posted September 22, 2021 This is certainly an ammonite. And I do think it has been deformed during burial, probably. The whole internal structure is messed up as is the outer shape. Interesting find. 1 Link to comment Share on other sites More sharing options...
tombk Posted September 22, 2021 Share Posted September 22, 2021 11 minutes ago, jpc said: This is certainly an ammonite For my curiosity, how do you tell it’s definitely an ammonite? Do you see suture lines? Would that be a distinguishing criteria to separate it from a gastropod? Thanks. Link to comment Share on other sites More sharing options...
Ludwigia Posted September 23, 2021 Share Posted September 23, 2021 13 hours ago, tombk said: For my curiosity, how do you tell it’s definitely an ammonite? Do you see suture lines? Would that be a distinguishing criteria to separate it from a gastropod? Thanks. For example: In the 2nd last photo at the bottom left, it is possible to distinguish parts of a septal wall, which gastropods do not have. 1 1 Greetings from the Lake of Constance. Roger http://www.steinkern.de/ Link to comment Share on other sites More sharing options...
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