Inland marine molluscs

There is someone posting observations of shells of marine molluscs from central Lincolnshire, about 55 km from the coast. No doubt they were wild, not cultivated. And no doubt he has correctly shown the place where he photographed them. But they clearly never lived there. Which data quality attribute should be given a thumbs down to stop them appearing as genuine observations of those species from that place?


Location is inaccurate.


It would be good to leave a note that the location looks wrong, and often users will correct it when they realize there is an issue. Just make sure to remove you’re votes if it’s fixed.


He has already had someone asking him to give the correct location so I’ve just flagged location as incorrect and will follow the observations.

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If theoretically you knew that those shells got inland without humans assistance, I would keep them as wild. Otherwise, the correct mark would be to mark it as captive.

This thread reminded me to tag @thomaseverest in an observation of what looks to be a large oyster shell found in the woods along the Willamette River.

Or, the point being, sometimes observations do happen in places they “shouldn’t”

I would consider them to be “Not wild”. But best advice is to ask the observer what was going on with these.

Looking at the elevation map it’s entirely possible that some of them may be remnants from when the sea level was higher and haven’t been fossilized.

The elevation around the town of Lincoln is only about 6 meters.

3 million years ago the sea level was about 20 meters higher than present. Around 5,000 years ago sea level was still increasing as a result of the melting of the ice from the LGM and actually peaked at 3-5 meters above present (different in different locations around the world), then dropped to present levels.

In addition, that portion of the UK has uplifted roughly 70 meters over the last million or so years - nore that the linked paper is referring to the Bristol area, which is SE of Lincolnshire, but that doesn’t change the results, if anything it means that the uplift in Lincolnshire would be slightly greater.

The upshot of all this is that when looking at things that preserve well and last for very long expanses of time (such as marine mollusc shells) it’s important to remember that even over relatively short expanses of time (geologically speaking) there have been large changes in sea levels, so it’s entirely possible that marine shells that look recent found in areas currently far from the sea are there naturally. Often elevation is a more important marker than distance.

An example of this is where I work in SE Asia. I had a team visit my work area to look at the active marine lakes here to see what their work area would have looked like 5,000-2,500 years ago when it was a collection of bays and islands. Their study area is now 40+ km from the ocean, but just a few thousand years ago it was under water.


True, but one of his collection is Crepidula fornicata, a modern introduction to UK. He has had the chance to explain if they are sub-fossils and hasn’t engaged.

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Not defending the fellow, but in my area I find fresh marine snail shells on top of 100+ meter cliffs, brough there by birds to open on the rocks. That’s an unlikely scenario in the cases you’re describing, but we do need to pay attention to oddities and natural movement.

Or that someone else may have moved it and the observer found it. In the US in inland areas I’d sometimes fine fresh marine shells mixed in with gravel.

Again, not defending the observation, but I find that people on iNat are sometimes overly quick to contest an observation (and in other cases overly willing to accept any observation or ID no matter how inappropriate).


They sound like bunch of shells that someone collected at the seaside and then dropped them inland for whatever reason. In my experience this does happen a lot.

Just because they were genuinely found by the observer at that location does not mean that they got there by natural means rather than by human agency.

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Thanks but yes, I realise that. I’ve set the location to inaccurate.

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