Petrified fossils can represent any number of different living things, such as plants, animals or even microorganisms whose tissues have been replaced by minerals. These fossils tend to be dark in appearance, and there is little to no organic material left in the fossil. Petrified wood is a common type of fossil that can be found all over the world. Dinosaur bones and the bones of other prehistoric animals are typically petrified during the fossilization process.
Mold fossils form when a living thing is encased by some type of material and then the tissues of the living thing break down while the encasing material fossilizes. The only thing left when a mold fossil is created is the basic imprint of the animal or plant, which captures the general outline and textures the animal or plant possessed while living. The impressions left within mold fossils can sometimes be incredibly intricate, allowing scientists to learn much about the plant or animal that created the fossil.
Whole animal fossils can be anything from prehistoric human beings to wooly mammoths, and they are among the most prized fossils because their DNA is intact. A forty-two thousand-year-old wooly mammoth was found frozen in ice in Siberia in 2007, and the amount of information gleaned from the discovery was enormous. Whole animal fossils have given scientists a much clearer picture of what occurred in the past and how animals coped with new developments in the ancient world. The amazing DNA discoveries are possible due to the fact that tissues are preserved rather than fossilized in whole animal fossils.
An imprint fossil is similar to a mold fossil in representing the shape or trail of a part of a living creature, but it forms as a result of contact, like a footprint, rather than encasing tissues that decompose.
A cast fossil occurs within a mold fossil and is the result of minerals or another substances occupying a mold fossil and creating a replica of whatever was molded. Cast fossils are very rare and are usually found in conjunction with mold fossils.