Well after that title, this should really be pretty self explanatory. One thing that is worth noting as it applies to almost every one of these things is just how amazingly convincing some things are. More than once I took pieces to people with years and even decades of field experience and a couple of times a debate ensured over whether or not it really was fossil bone.When you see something at a distance, even just a few metres away, you go and check it out, and while its mostly easy to tell almost instantly once you have picked up the item in question, it is still a pain. When that means a long walk or a tricky climb to get to some inaccessible smudge that might just be bone, it can get very annoying and waste a lot of your time. And of course it is very easy to do, since you are actively looking for bones that might be broken, eroded, distorted and stained or bleached and thus not look mch like what you might expect, meaning you have to check out something that looks only very vaguely like bone, just in case it is. Add to that the huge range of shapes that one does expect (think teeth, jaws, ribs, bits of vertebrae, parts of skulls etc.) and of course pretty much anything white on the surface becomes worth checking out.
Extant bone – Obviously this looks a lot like fossil bone and it’s texture and weight is a give away once you pick it up, apart from the smallest fragments.
Wood – You would be amazed how many pieces of dried wood and twigs make a near perfect copy of longbone shafts.
Roots – Roots protruding on the surface, or more commonly that have died and rotted inside the ground can look just like bone fragments. It’s a real pain when you spend ten minutes carefuly brushing and digging around a bone fragment attached to a possible skeleton only to discover it branches.
Trace fossils – Lots of fossilised burrows are a different colour to the surrounding matrix and typically a much lighter colour or even white and again can look like the shafts of longbones at a distance either poking out of overhangsor lying on the surface.
Minerals – All kinds of bits of minerals poking out of rocks are white in colour and simply depending on how they are exposed can make you double take.
Salt stains – Salt accumulates on the surfaces of soem exposed rocks in large irregular white patches. Guess what some of them resemble?
Rocks – White rocks abound. See above.
Plaster – The area we were working in has been heavily explored in the past and fossils collected. Those who went before covered their fossils in protective jackets of white plaster jsut as we did. Inevitably bits fall off, and stain or dry on the surface. Unlike many of the other things here, these bis of plaster are of course often found in large numbers, spread out over quite a large area, and in or next to a layer of rock that you really would expect to find bone in. Thus they really stuck out as looking like good sites from a distance, and indded must have been originally since someone else obviously took out something there leaving the plaster behind.
Plastic etc. – Bits left by previous expeditions or local farmers can again fool you if they are exposed in the right way or have eroded into a familiar shape.
Bird waste – Another insidious one. Obviously many birds (and indeed bats) use some roosts repeatedly and thus a build up of wastes under those perches is somewhat inevitable. These leave nice streaks just on the surface of the rocks, or little piles on top of them that can look just like weathered fragments of bone.
That is about all I can think of, probably going to a different site will eleminate a whole bunch of these and instead throw up new ones. I hope my eye will improve with a bit of experience, though as I said it was conforting to my ego to see other fooled with almost every one of these at some point. If nothing else it demonstrates just how many bits of vertebrate skeletons look like wood, plastic, plaster, salt stains and more.