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Many years ago, I found a piece of rock on a lakeside in Switzerland (see picture below). I think that it could be a "fossil" from some Pecten species (do you agree?).

My question is: how old such a fossil can be, approximately? Is it like 1000 years, or rather 1'000'000 years?

I have no idea, that's why I just would be interested to have your opinion on this topic. I don't know if it is frequent or rather uncommon to find such "fossils".

Thank you for your help!

pecten

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Pectens seem to have evolved from Chlamys in the late Eocene or early Oligocene. The coarseness and rib spacing of Vertipectens has been slowly evolving since the early and Mid-Miocene, so they have been around for at least 16 million years, maybe up to 20 million years. If you want to be precise you will need to read-up on the fine detail. Pectens are a classic case of 'ontogeny recapitulating phylogeny', and their identification is complicated by parallel and convergent evolution of different species. As fossils, they are quite common, and probably more useful as indicators of the palaeo-environment, than as age indicators. Where you find such fossils you will very likely find associated micro-fossils in the same rock, which are more diagnostic of age.

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    $\begingroup$ I thought I'd found a Pecten in the chalk at Barrington (Cambridgeshire, UK) - Cretaceous age. I never did a formal identification, but if Pecten really did appear in the Eocene, then there were Pecten-like bivalves in the Mesozoic... $\endgroup$ – winwaed Aug 31 '16 at 12:58
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    $\begingroup$ I suppose it depends upon how much change you are willing to accept and still call it the same species. Superficially similar fore-runners of the modern pecten can be found right back in the early Mesozoic, but were technically different species back then. $\endgroup$ – Gordon Stanger Aug 31 '16 at 13:35

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