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dinosaurbero

Fossils Or What?

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dinosaurbero

I have taken a photograph of some peculiar traces or artifacts on an early Cretaceous carbonate beach. I can't figure out what they represent.

You can see the photograph on my blog.

http://mesozoicmosaic.blogspot.com/

Any suggestions, please?

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4circle

Well, the chain of circles is not a fossil - it's a recent artefact - the homescar of a limpet. In the tidal zone, limpets hunker down firmly when the tide's out, and only move to feed when submerged. They then return to the same homescar as the tide turns and waters recede. The scar bears the characteristic shape of the limpet shell.

We can see they're recent artefacts as they cut through the darker encrustation on the carbonate surface.

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dinosaurbero

Thank you very much 4circle. A limpet would be a perfect answer if the place wasn't so far from the tidal zone. They don't come so high and far away from the water. Only very high waves can reach this place. However, I could imagine a loose limpet being tossed away by some very powerful wave ending on this place. It is possible, indeed.

What about the long grooves?

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4circle

The groves are not really determinate I'm afraid. They're clearly syngenic (formed at the same time as the carbonate) but beyond that it's not possible to tell without much closer views I'm afraid.

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Auspex

...A limpet would be a perfect answer if the place wasn't so far from the tidal zone...

At what point in its history might this rock have been awash in the tides?

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dinosaurbero

That is hard to tell. This spot was certainly a tidal zone 100 million years ago (ripple marks). Now it is some 5-6 meters above the sea level and some 10-15 meters away from the sea. On the other hand the high tide is only about half a meter here.

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4circle

Limpets can quite happily live above the high tide mark as long as they only move around at night or when it's wet. They rely on mucus to remain moist. Living further from the littoral zone reduces risk from aquatic predators. See: J. Exp. Mar. Biol. Ecol., 1985, Vol. 89, pp. 283-296 who make the distinction between "submersed" and "emersed" limpets.

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Taogan

I am suspicious about calling the circles limpet scars, they could be but to have 5 in a straight line and then another 5 in another straight line and no others? I would look into a man made origin, some sort of stand or support with metal feet? Agricultural? Military? Fishing? Limpets can live in straight lines but usually not on their own and nature can be neat like that but it would be unusual.

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dinosaurbero

Thanks, Taogan. I think we're approaching the right answer to the mystery. It may be of human origin. Most likely military. Pula was a naval harbour. The flying boats were based in the same bay where this artifact is. Just about a hundred or so meters away.

More images and conclusions on my blog:

http://mesozoicmosaic.blogspot.com/

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