Paul Armstrong's picture

Ammonite puzzle

Observed: 13th April 2008 By: Paul Armstrong
S159 Neighbourhood Nature - course complete

Any idea how an ammonite fossil can form superimposed upon another?

  • Ammonite
    Confidence: I'm as sure as I can be.
    ID agreements (): 3 People
    • PhilT69
    • rimo
      Bumblebee Conservation TrustUK Ladybird Survey
    • hughcarter95
  • ammonite
    Confidence: I'm as sure as I can be.
Species interactions

No interactions present.


BeckyH's picture

By having one ammonite

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

Paul Armstrong's picture

Still not sure

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?

BeckyH's picture

Very unlikely ... without

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.

Paul Armstrong's picture

Thanks for the explanation

Thanks for the explanation, Becky.

BeckyH's picture

Did that make more sense? I

Did that make more sense? I hope so! :)

Paul Armstrong's picture

Made sense

Thanks Becky - Yes I can see now how the fossil could have been made.