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Common Types of Fossils

Fossils are the remains of ancient organisms. There are two main types of fossils, with several sub-types within each category. A body fossil is a fossil that shows the structure of an organism, while trace fossils show patterns of activity that were carried out by organisms. Fossils are found in many locations around the world and are preserved in a variety of ways, such as in volcanic ash or embedded in slate.

Gastroliths
- Gastroliths are gizzard stones that are fossilized. This type of fossil is generally found by researchers who are studying reptiles. The stones are commonly found in the gizzards of organisms, but only considered gastroliths when found in reptilian remains. One way for a researcher to tell if a gastrolith is authentic is if the stone is found in bones and situated where the stomach should have been. The stones can reveal a lot about the feeding habits of ancient reptiles.
Mold and Cast
- Mold and cast fossils are common types that occur when an organism is buried under many layers of sediment decays. The impression left behind is known as the mold, while an entire space left behind that has filled with sediment is called a cast. The bones of dinosaurs commonly fall into this category.
Carbonization
- Carbonized fossils are another common fossil type, which occurs when carbon-containing organisms are buried and compressed. The result is a black mold that occurs when heat and pressure turn the organism to coal. Insects. leaves, feathers and fish are among the organisms found as carbonized fossils.
Tracks and Footprints
- Tracks and footprints are commonly left behind when animals made their way through the mud during prehistoric times. The area where several preserved tracks from the same animal is known as a trackway. The path may also have impressions of the animal's tail or other body parts. Such tracks are commonly found in the states of Texas, Arizona and New Mexico.

Artifacts