Fossil Shells Or Just Shells?

[katfran]

Ok, this may seem like a really dumb question, but how do you know if a shell you found is a fossil or just a shell?

Reason I ask is because I was in Aruba many years ago on the North side by all of the famous caves. The water was at least a half-mile away but the open desert land from the caves to the water's edge was littered with dry, sun bleached shells, coral and the like. I picked up a few pieces and brought them home (probably shouldn't have but I was real young and no one stopped me). It occurred to me that that "litter" was probably deposited there and left behind from before the water receded and who knows how long all of that was left there. I also found top shells in the caves. Also, every once in a while I find a shell on the beach that just seems extra old, worn, and hard - could it be a fossil? I have no idea.

So my question is, how do I know if what I found are fossils or just shells - what makes a fossil shell a fossil shell?

I have no way of knowing what the shells are made of, and I have had no luck in identifying any of them. I know that if I could identify a shell that is extinct it would be a clue. Are there other ways to know if a shell is a fossil or not? Does anyone know anything about what can be found in Aruba?

Thanks! Kat

[Guest N.AL.hunter]

There is no one accepted definition of what is a fossil. I have seen it defined as "evidence of past life", but that would indicate that roadkill can be considered as a fossil. Some say it must have been entombed in some way inside a type of matrix (sand, rock, ice...), but that would exclude mummification of sloth remains found in caves. So, are your shells fossils? Can't say, but you are correct that if that species isn't found in that area any more, I would call that a fossil for sure.