Actually, your analogy is probably the explanation that I grasp best; “how old is old?”

The more ‘vague’ definition of fossil explains Dr. Mary Schweitzer calling demineralized tissue from a T-Rex bone ‘fossil’ where I would have just called it ’tissue’. I guess both are correct?

But this does undo a long held assumption of mine – that ‘real’ fossils were mineralized and that everything else was just ‘well preserved.’ I never asked myself at what point in the mineralization process does the subject become a fossil. Time for some reading!

Your confusion is understandable. “What is a fossil?” is a bit like asking, “How old is old?”

Here’s a passage that sums up the situation nicely, from the Audubon Guide to North American Fossils (p.13):

“Paleontologists disagree about how old a specimen must be before it can be called a fossil. Some require that it merely be older than historic time. Others stipulate that it must date from before the start of the geological epoch known as the Recent, or from at least 11,000 years ago. If a a plant or animal is extinct, its remains are usually considred a fossil even if they were buried only 100 years ago. If such remains are relatively recent and have not yet been mineralized, they are sometimes called subfossils.”

I find the term ‘Fossil’ as used in this article confusing. Forgive an electrical engineer for being out of his depth in biology – but I thought that fossilization only applied to matter preserved through mineralization. It was my understanding that this process took a lot longer than 3000 years.

Am I incorrect? Were these Dodo bones already mineralized, or partly mineralized? Can ‘fossil’ be applied to bones this early in the process of mineralization?