I've spent quite a bit of time in the wild, but I've seen little to no bones lying on the ground. Large bones such as skulls, spines, horns, hooves are not eaten by any other animals, and even microorganisms. thanks to which they can persist for decades on the ground surface. Especially in hot and dry climates, steppe and desert regions, as well as in the arctic. Therefore, it should be expected that a large number of bones will be found on the surface of the soil, also underground in the topsoil. But nothing like this actually happens. Where do the bones of dead animals go?
Even a superficial Google search will tell you by the title of the hits you get that bones are eaten, e.g. my top hit.
Osteophagy simply means bone eating. I'm not sure why it applies to herbivores in particular; maybe because it seems to be strange behavior in an herbivore, whereas it's expected in a carnivore.
Phosphate is crucial to life, but isn't abundant in 'edible nature' (plants, etc.). It is abundant in bone, however, and because it is crucial to growth and energy production, animals eat bones however they can. Some animals, e.g. those without teeth, will swallow small bones whole. Carnivores and capable omnivores will crush susceptible bones by chewing on them; herbivores will just grind away at them and consume the bits they can generate.
From Wikipedia, a cow chewing on a bone.
How about a squirrel?
Or a deer eating human bones:
This answer could be longer, but why go on? The answer is obvious.
Let's look at the decomposition of a corpse as a whole.
- Active decay
- Advanced decay
- Dry state
You can skip to the dry state, which answers your question specifically.
A prerequisite to studying decomposition is knowing that decomposers break down organic material by secreting enzymes turning it into dark liquid form that's possible for them to absorb. Foul gases are produced in the process.
Also, it's best to think about decomposition as a bunch of processes caused by several agents happening and progressing at the same time.
When you hear fresh state, think of anything that ends with mortis:
- Algor mortis (decrease of body temperature to ambient temperature)
- Rigor mortis (temporary stiffness of muscles due to decreased ATP which is required to relax muscles until decay starts)
- Livor mortis (pooling of blood at the site closest to the ground)
Bloat happens because gut flora starts breaking through the wall of the gut. The wall is normally protected by the epithelial cell layer which has a high rate of shedding and regeneration. Since regeneration stops, flora can now bypass into the underlying tissue and start feeding on the body from the inside which results in the formation of
- Gas (has foul smell)
- Liquid (dark purge fluid that leaks through orifices because of increased pressure from gases in the intestine)
Autolysis also starts where lysosomes containing lysozymes break up and release the hydrolytic enzymes which break down tissue so skin slippage may occur.
Liquifaction by decomposers continues causing darkening and loosening of the exterior.
Blowflies are attracted to the foul smells (even the smell of excrement) and thus, approach the corpse early and lay their eggs which hatch releasing maggots that feed on the corpse.
Several species of insects also start feeding on the corpse but that starts later.
Adipocere (corpse wax) may also form from decomposition of fat preventing further decomposition.
In advanced decay, most tissue has liquified and loosened.
What remains from the corpse is the dry or skeletonised state. Dry here indicates that all the liquid produced from the action of decomposers has been taken up and what remains is the hard tissue, bone or the skeleton.
If the skeleton becomes covered in soil, scavengers (animals) do not eat it and it breaks down in acidic soil over a long time period.
If the soil is neutral, it takes much longer time for this to take place.
If the soil is
- dry, anoxic or slightly alkaline (unsuitable for decomposer activity)
- salty (has minerals which can form long-lasting hard structures)
the bones may fossilize.
they rot, get eaten, or get weathered away. Under extremely rare circumstances they fossilize.
What you are talking about is called bone taphonomy.
You can do a simple experiment yourself, put hooves or bones partially buried in dirt in your yard and check on them from time to time, depending on where oyu live what happens will vary quite a lot. Paleontologist and forensic scientists have studied this a lot to understand fossil and human remains respectively.
What happens to them
Normal erosion processes and soft tissue decomposition break the bone in to smaller pieces. The same thing that breaks down rocks breakdown bone just faster. Physical and chemical weather all work on bone. Bone is soft and permeable as rock goes so it weathers very quickly.
Bacteria, insects, fungi, plant roots, or other organisms break them down and eat them. You can prevent this by drying the bone out and keeping it away from soil, (soils keeps the bone moist and makes it easy for those things to reach the bone) Bone like any organic material rots, oxygen and water make it happen faster and bigger organisms can eat them faster.
You can see the same thing with any organic material which is why we dry meat and fruit to preserve them. Also why we cover organic materials like leather or wood in oils to keep them dry. or cover them in poisonous chemicals just like you can do with bone, it slows down their decomposition. in really dry places or conditions with no oxygen bone can take very long to decay. A cow skull defleshed and nailed to a barn in the desert will take a very long time to decay centuries or longer, a bone left on the jungle floor wet and covered in dirt and leaf litter will be gone in months, assuming you can keep things from eating it, (bone is a high demand resource in forests where phosphorous is in high demand).
Different materials decompose at different rates. Under absolutely perfect conditions the bone does not decay completely, creating a fossil. I personally have pulled unfossilized mammoth bones out of clay rich desert soil in Wyoming, the bone had all the structural strength of dry rotted wood, any handling caused bone to flake off, but it was still a complete mammoth leg bone, its decay had been severely slowed by dry, cold, anoxic conditions. We do find lots of buried bone in the right environments.
Soils is not static
If you put bone on top of soil it will not stay on top of the soil. soils turns over due to thermal, erosional, and biological forces. things get buried, see frost heaving and soil creep as examples. Soil is not static it is always on the move. Deserts in particular tend to be highly erosional, which is why we look for fossil in deserts, new rock is constantly being exposed and destroyed.
Now deserts and cold regions do have much slower rates of decay which is why you can find remains that are decades or even centuries old in such places. Bones are found in bogs and permafrost for instance. things like sunlight, temperature, abrasion, weather and such can all breakdown bone. Also you vastly overestimate how many animals there are in such places, even if all their bones did not decay they still would not make up a noticeable portion of the topsoil. in places where the animal remains are that common they do make up a significant portion of the soil we call those coral sand beaches, where mechanically broken up animal shells make up the majority of the soil.
Sources about bone decomposition and diagenesis
Sources about soil and erosion turnover
When you study archaeology, you dig and find everything becomes buried very fast through burrowing and overgrowth subsidence. You can find a lot of bones when you walk a minute away from the beaten track, and very rarely on paths, often gray and beige. Humans very often move nice skulls as trophies.
Skulls provide a microclimate for moss, ants, beetles, plants, low-wind zones and snags to collect leaves. Humans like to pick them up and move them, rodents gnaw them, the jaw tumbles away, bug and bird droppings, acids and humidity dissolve them, frost cracks the pores.
Plants compete for space and grow around bones and hide them. Bugs dig networks of burrows and make the soil cave in a bit, worms place middens on the sides, A hoof or a femur will be covered by wild grass in 3-5 years, a horse skull in 10-20 years.
In the arctic there aren't horses, cows, deer, only seashore megafauna. Bones get snowed over. Else they are subject to freeze-thaw weathering, water stays in the pores of the bones, freezes and expands every day, and erodes them.
In the forest, leaf fall and sticks accumulate 1-5cm every year, trees fall over, the soil is alive with fungus mycelia and bugs, It's also quite an acid environment. Bones would be expected to stay uncovered for less than 15-20 years.
In the desert, there aren't lots of big animals, and the bones can last a very long time there, we can find awesome cadavers in regions of low biological, geological and glacial activity.
Human transportation near paths Scavenging Animals hide away when they are ill Gnawing Moss Freeze thaw Geological activity Subsidence Glacial activity Sand dunes Trampling by other animals