What could this be? Just a rock or a fossil as i have theorized. My guess is that it could be a kind of marine fossilized arthropod, with fossilized inner organs, i know it is not very common but thats what makes more.sense to me.
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It was found in the rivershore in Bilbao, in lower cretaceous sediments, i found some sea-urchin fossils there too.
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Thanks a lot!