What is the difference between preserved bone and permineralization of bone

There are two main types of fossil preservation, with alteration and direct preservation. Most common is fossil preservation with alteration; the original organic material is partially to fully changed into new material.

There are several types of preservation with alteration:. The second type of fossil creation is direct preservation, the preservation of original organic materials. The most common directly preserved fossils are unaltered hard parts of a living organism, like shells, teeth, and bones. This material is unchanged, except for the removal of less stable organic matter. Other examples of this type of preservation include fossil corals, shells, sponges, microscopic fossils and a host of other organisms with hard parts.

In rare circumstances, preservation of the soft parts of an organism may occur. After a bone, wood fragment, or shell is buried in sediment, it may be exposed to mineral-rich water that moves through the sediment. This water will deposit minerals, typically silica, into empty spaces, producing a fossil. Fossilized dinosaur bones, petrified wood, and many marine fossils were formed by permineralization. In some cases, the original bone or shell dissolves away, leaving behind an empty space in the shape of the shell or bone.

This depression is called a mold. Later, the space may be filled with other sediments to form a matching cast in the shape of the original organism. Many mollusks bivalves, snails, and squid are commonly found as molds and casts because their shells dissolve easily. In some cases, the original shell or bone dissolves away and is replaced by a different mineral. For example, shells that were originally calcite may be replaced by dolomite, quartz, or pyrite. If quartz fossils are surrounded by a calcite matrix, the calcite can be dissolved away by acid, leaving behind an exquisitely preserved quartz fossil.

When permineralization and replacement occur together, the organism is said to have undergone petrification, the process of turning organic material into stone.

However, replacement can occur without permineralization and vice versa. Some fossils form when their remains are compressed by high pressure. The Greeks named them ammonites after the ram god Ammon. Similarly, legends of the Cyclops may be based on fossilized elephant skulls found in Crete and other Mediterranean islands. Can you see why Figure Many of the real creatures whose bones became fossilized were no less marvelous than the mythical creatures they inspired Figure The giant pterosaur Quetzalcoatlus had a wingspan of up to 12 meters 39 feet.

The dinosaur Argentinosaurus had an estimated weight of 80, kg, equal to the weight of seven elephants! Other fossils, such as the trilobite and ammonite, impress us with their bizarre forms and delicate beauty. A fossil is any remains or trace of an ancient organism. Fossils include body fossils , left behind when the soft parts have decayed away, as well as trace fossils , such as burrows, tracks, or fossilized waste feces Figure Figure The process of a once living organism becoming a fossil is called fossilization.

Fossilization is a very rare process: of all the organisms that have lived on Earth, only a tiny percentage of them ever become fossils. To see why, imagine an antelope that dies on the African plain. Most of its body is quickly eaten by scavengers, and the remaining flesh is soon eaten by insects and bacteria, leaving behind only scattered bones.

As the years go by, the bones are scattered and fragmented into small pieces, eventually turning into dust and returning their nutrients to the soil. On the ocean floor, a similar process occurs when clams, oysters, and other shellfish die.

The soft parts quickly decay, and the shells are scattered over the sea floor. If the shells are in shallow water, wave action soon grinds them into sand-sized pieces. Even if they are not in shallow water, the shells are attacked by worms, sponges, and other animals Figure For animals that lack hard shells or bones, fossilization is even more rare. As a result, the fossil record contains many animals with shells, bones, or other hard parts, and few softbodied organisms.

There is virtually no fossil record of jellyfish, worms, or slugs. Insects, which are by far the most common land animals, are only rarely found as fossils. Because mammal teeth are much more resistant than other bones, a large portion of the mammal fossil record consists of teeth. This means the fossil record will show many organisms that had shells, bones or other hard parts and will almost always miss the many soft-bodied organisms that lived at the same time.

Pyrite formation requires an absence of oxygen or the iron would oxidize in reducing conditions, usually acidic. Replacement by silica silicification also requires acidic conditions and an abundance of silica.

The coral and algae have been silicified. Replacement by calcite is very rare. The original shell material would be silica or phosphate.

Calcification requires alkaline conditions to dissolve the silica and induce deposition of calcite. We have no examples of calcified fossilization. Carbonization: the soft parts of the organism were compressed and heated, driving off all the volatiles H, N, O. A carbon film is left behind. Most common in plants, soft-bodied organisms, organisms with phosphate skeletons, organisms with chitin skeletons, and sometimes fish under the right environmental conditions.

Each organism here had a proteinaceous skeleton or framework the trilobite skeleton also contained a layer of calcite. During lithification, pressure and high temperatures volatilized the N, H and O of the protein, leaving behind a black carbon film. Imprints are left when an organism is pressed into soft sediment. The original hard parts may be gone, dissolved after burial. Very shallow imprints are called impressions, as of the fern leaf.

Larger organisms may leave molds or casts. A mold is the imprint left by the organism, and is a negative of the organism. Molds may be external - of the exterior of the shell, as on the slab of snail and clam external molds. If a shell fills with sediment that later hardens, it forms an internal mold a 3-D picture of the space inside the shell.

If an external mold later fills with sediment or minerals, it can form a cast. Trace fossils are other kinds of evidence that an organism existed.

Trace fossils include tracks, trails and footprints; burrows and other dwellings; tools; coprolites fossilized excrement ; and chemical fossils, which is chemical evidence of the existence of an organism. One of the most common but least useful kinds of trace fossils is bioturbation, evidence that organisms have churned through sediment. Bioturbation is recognized by the complete lack of sedimentary structures such as laminations and cross-beds, or by chaotic structures within the sediment.