Animal bones in archaeology

(A basic introduction)

Animal bones can give us lots of good information about the lives of our ancestors. Bones are often well preserved in soil and this is a great help to us.
What can animal bones tell us about the past?
Bones tell us what animals were in the area being investigated.

This is important because it tells us something about local conditions.

For example, We know swans live on rivers and ponds, and we can guess that they did the same in the past, so if we find swan bones we can at least assume that the area wasn't a desert at the time. Of course we must remember that we cannot prove it because we weren't there (and besides, the bones might have been brought to our imaginary desert site from far away), so archaeologists are usually careful about saying anything more than "bones provide an indication of environment."
Bones can tell us about how people survived.

For instance we can tell if a particular settlement was based on either hunting or farming. Domestic species such as cattle, goats etc would indicate a farming culture, while lots of wild boar bones is a good indication of hunting. Of course we have to be careful and it is easy to imagine how farming communities end up with boar bones and hunters with cattle bones, so again we talk about "bones providing an indication of subsistence practices."
Bones can tell us about which meat was important in people's diets.

This is a nice easy one. If we find a huge pile of cattle bones we might reasonably suspect a butchery event. Therefore, the people ate beef... but be careful (remember that in India today there are many cattle, but few Indians eat beef.
Bones can tell us about trade

If you find bones of animals that came from a long way away (eg: Lion bones in a medieval pit in london) you can be sure that they got there somehow. Archaeologists use such clues to discover more about who was trading with whom in the past. To use the technical terms, "archaeologists can use frequency of bones of non-local species as indicators of trade routes."
Bones can tell us about what people believed

When we find red ochre sprinkled on paleolithic human remains this must tell us that the early humans were affected emotionally by death. A ritualised act like this says that the mourners felt a death needed to be commemorated.
What can we learn by looking more closely at bones?

We can look at bones under a microscope and sometimes find cut marks from where knives have been used to butcher the carcass. The great news is that Iron, Steel, Bronze, Copper and Flint all leave slightly different marks and we can learn about the tools being used in this task. This can help set dates for excavations.

Sometimes we find the bones attached to skins. Looking at modern tannery methods we often find feet attached to hides and so we can deduce that (perhaps) the site where feet are attached to hides is the site of a tannery.
Anything else?

Yes, we haven't even started. There is masses of valuable information we can glean from animal bones, and we hardly even started looking at what human bones can tell us.
How do we clean bones?

This depends on the soil conditions, bone age and species. Some small bones have to be treated as carefully as any precios find, but many bones of cows, horses sheep and goats can be cleaned quite vigourously with a scrubbing brush and water, even after a couple of thousand years under the mud.