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Why Some Dinosaur Bones Last So Long: The [Surprising] Fossilization Process

Dinosaurs roamed the earth over 65 million years ago, but somehow their remains are here for us to study. Not every creature’s bones become fossilized, so why do some dinosaur bones last so long and others don’t? It’s amazing to think they have lasted so long, some skeletons are even more than 70% complete.

So, why some dinosaur bones last so long? The shelf life of bones and other hard remains is actually more complicated than you might expect. Our bones aren’t soft like the rest of our bodies, so they are less susceptible to deterioration and rot. But if every bone or tooth lasted forever, they could be found in every inch of the earth. Some bones last millions of years while others can deteriorate in less than a decade.

Why Some Dinosaur Bones Last So Long: The [Surprising] Fossilization Process

To understand why some bones can last millions of years, we need to first get a grasp on why so many do not. So, we need to answer the question of if bones actually deteriorate and, if so, what conditions they need to be in to do so. 

Do Bones Deteriorate? Why Some Dinosaur Bones Last So Long

If you have ever seen the catacombs, you may believe that our bones will remain forever. Ashes to ashes, dust to dust. Eventually, all of our bodies deteriorate, but why does it seem like bones last forever?

Bones are made of collagen and calcium phosphate, a combo that can last a very long time. Even in the worst conditions, in fact, bones take at least a few years to decompose. These conditions need to by warm and wet, drawing in bacteria that attack the collagen which breaks down the structure of the bone.

In dry environments, like the catacombs or our modern caskets, bones can last hundreds of years. This is why that small part of the population of a group is preserved. In the case of the Egyptians, these people of high class and nobility were placed in environments specifically made to stop any rot from progressing.


If mummified or put into an extremely dry place with very little oxygen, the body’s deterioration time can be extended by thousands of years. This is the case because that bacteria cannot survive in cold or dry places and are especially useless in places without enough oxygen.

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It explains why burial grounds like the pyramids can hold remains for extremely long periods without decomposition. These specific conditions are also part of why the modern casket of today exists.

But what about bones that we find from millions of years ago, like those of the dinosaurs? None of these bones are being kept in places that are specifically cold, dry, or without oxygen.

A vast majority of the dinosaur remains that we discover today are found at the bottom of bodies of water, or in the middle of places where the climate is very warm. So, why didn’t they decompose?

Methods of Preservation

The dinosaur bones that we find are not actually bones at all, but fossils of bones. You may have heard dinosaur bones be referred to as fossils, but you may not know that fossils are not actually bones at all. The fossilization process is a very specific and complicated one. There are a small variety of different processes that can possibly happen.

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As with some of the mammoths that we have found in ice over the last few decades, sometimes remains can be completely frozen in ice. While this is sometimes referred to as fossilization, the results would probably be more in line with mummification. This is the case because much of the soft tissue is still present on the animal.

The idea of freezing our bodies for eternal preservation has been swimming around our species’ subconscious since the relationship between temperature and rot was realized in the 1860s. The problem here and the reason why this is not really fossilization is that freezing a body doesn’t really make it eternal.

Freezing something only preserves it as long as the ice remains, but ice is not an incredibly reliable factor. True fossilization, on the other hand, does guarantee that the remains stay completely intact forever.


Amber is another way that remains can stay intact for millions of years. Amber is crystallized tree sap that sometimes encases small insects.

The amber hardens and can last for millions of years, leaving the body of the insect completely untouched inside. This is a different process as well and is far more complicated to comprehend, but it is more in line with the definition of fossilization.


When we refer to dinosaur bones, however, these two options are not really what we are talking about. Dinosaur bones truly fossilize, which means that they are encased in sedimentary rock.

The Process of Fossilization

Sedimentary rock is formed by sediment (a combination of many tiny pieces of different minerals) hardening. Sediment forms as it moves from place to place by way of water, wind, or ice.

The sediment that is moved by water usually ends up under bodies of water, while sediment moved by wind can be found in places like badlands.

When a dinosaur bone is encased in sedimentary rock, the moisture from the surrounding sediment infuses the bone with these minerals. This, essentially, turns the bone to stone.

After the process is undergone for millions of years, there isn’t really any bone left and the only way for the fossil to “deteriorate” is for it to wear down through erosion.

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Fossil Deterioration

Erosion can happen but is very unlikely due to their incasing in the sedimentary rock. This rock is usually left basically untouched under the surface of the earth, as they can only fossilized in areas of little vegetation, thus very little life in the surrounding ecosystem. The only creatures that would disturb the rock where these fossils can be found are humans.

We find the sedimentary rock beneath the surface and very carefully excavate the fossils, trying to disturb the form as little as possible while still retrieving it from the rock that it is encased in. This is a very difficult and time-consuming task, which is why most who do it dedicate their lives to it.

If these fossils are excavated before they wear down, they have no chance of further erosion and will last basically forever.

Even if they are in a warm or damp environment, they are no longer made of collagen and calcium phosphate, so there is nothing for bacteria to feed on. They are simply mineral.

The Amount of Dinosaur Fossils

Lastly, I think it’s important to discuss why dinosaur bones are the bones most found as fossils. While there are many different kinds of fossils that have no relationship to dinosaurs as a species, we do have to recognize that many fossils are indeed dinosaur remains. This probably just has to do with the eras in which they existed.

At that time, there weren’t any precautions against things like massive mudslides or floods that could cause animals to both die and be buried with sediment.

This left many of these animals dying in those exact conditions, making the fossilization process more common among their remains. Thus, there a lot of the full-skeleton fossils that we find today are of dinosaurs.


The overall message to find in all of this information is that bones, like every part of a living organism, will return to the earth eventually.

The only exception is that of fossils, which after fossilization aren’t actually made of bone any longer. Some bones do last longer than others due to their environment and conditions, but even then, they are definitely not eternal.

Fossilization is also not a process that happens simply or frequently. There are so many little factors that need to line up naturally for the fossilization process to occur and it takes thousands, possibly millions, of years to entirely become a fossil.

While fossils are amazing and give us a piece of a time that we will never see, they are also a reminder of that circle of life. To break that circle, it seems, life must be taken out of the equation leaving only stone.  

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