Any idea how an ammonite fossil can form superimposed upon another?
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By having one ammonite resting on top of another one on the sediment after death - these would then lie together as they got fossilised and squished, and hey presto, ammonites on top of each other
Thanks for the suggestion, Becky, however I still don't understand how the two fossils effectively 'intersect' each other.
Could it be that the ammonite settled in muddy sediment, created the first impression, was moved by the current, made the other impression slightly offset from the other. Finally a dump of sediment covered the whole lot and was eventually lithified?
Very unlikely ... without trying to wriggle out of one particular method of preservation, these things really do depend on how the fossil is preserved - whether it's preserved as an imprint, or how the body itself is preserved.
In Yorkshire, as with your specimen, a lot of ammonites are simply squashed flat on the surface of shales. Some deposits contain mass deaths of ammonites, so you could imagine an ammonite in the silty seafloor having another one die above it, and float down to lie across it - these would then settle together in the sediment and be squashed. Or, more likely I would think, one ammonite settles and starts the process of becoming a fossil, and then has another ammonite settle on top of it. This then starts to be squashed too. During the fossilisation process, some features of the underlying ammonite will show up because of different mineralisation or slightly tougher bit of skeleton etc.
It's the same as if you draped something over a textured surface and pressed the two together - some topography from the underlying surface will show through.
Thanks for the explanation, Becky.
Did that make more sense? I hope so! :)
Thanks Becky - Yes I can see now how the fossil could have been made.
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