The Rarity of Animal Fossils

Wednesday, February 9, 2011

It has been estimated that 99% of any plant or animal species that ever existed is extinct now and never left a trace in the fossil record. Animal fossils are much more than just bones turned into stones in museums.

Fossils can be any trace, feces, footprint, and burrow of an animal. Animal fossils with the most preservation of soft body tissue are usually found in soil or ice that has been frozen for extremely long periods of time, in amber, or dehydrated in a very dry cave. Basically any condition that prohibits many bacteria from existing will result in a good fossil. Examples include animals that died in a cold swamp in Denmark and even mummies. In this case the animal fossils were preserved because bacteria could not survive in anaerobic environments. However, many environments are ideal for bacteria- so animal remains are often decomposed before they are allowed to fossilize.

In some really rare circumstances, both soft tissue and bone can be mineralized. In 2001, a 77 million year old duck-billed dinosaur fossil was discovered in Montana. This fossil had many of its soft muscle and skin tissues preserved and like similar dinosaur fossils it was a very rare find.

If an animal fossil is going to form, the first thing that must happen is that its body cannot be returned to the environment through decomposition, being eaten or other natural causes. Most good animal fossils are formed when the organism is buried quickly after death in a very deep and protected place. The most common parts of an animal to be preserved are the dense bones, shells, teeth or anything that is difficult to decompose. Animals like jellyfish are very rare fossils.

After the animal dies, the organic parts are eaten by bacteria and the brittle porous bones are left behind. These bones are made up out of inorganic materials and some organic materials like fats and proteins. Water drips down from above and pulls the mineral salts out of the bones. Over many years, minerals like calcium carbonate, silica and iron compounds solidify the bones into animal fossils that are as hard as rock.

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