Fossils and Fossil Types

FOSSILS AND FOSSIL TYPES

Fossils take some experience in identification of them. The easy-to-see fossil as a perfect specimen does not show up every time you see a rock; in fact, these are rare. There is more than one type of fossil you might encounter. Here are some examples:

Body fossil —this is a fossil you get with the entire organism trapped in amber, which is fossilized tree sap. Bones and teeth last longer in any fossil, including these, but body fossils trap the entire insect or other small creature. Figure 15 is what this looks like:

Figure 15.

Molded fossils —these are also called casts. This is the imprint of a shell or bone on a harder rock that then gets layers of sediment dumped on it. A shell might have an internal mold or external mold, depending on how it is laid out. Internal molds are seen when the inside of the shell is seen, while an external mold is when you see the bone or shell as it looked like on the outside. Casts are seen when molds fill with sediment.

Petrified fossils are those that have rock materials like silica and calcite fill in where the organism's remains once were, making a perfect example of the item but in mineralized form. This process, called permineralization, happens to things like trees. Figure 16 is a good example of a petrified animal:

Figure 16.

Footprints and trackway fossils —these are also called trace fossils because they just show how the animal lived and moved, but not the animals themselves. You might see footprints or evidence of a tail dragging.

Fossilized feces —these can say a lot about what any animal may have eaten. These are also called coprolites. Because feces tend to decay, these are very uncommon among fossils. You might find bones, shells, or teeth in them, among other things.

Carbon films —these are thin layers of carbon you'll see when you have an animal or plant that leaves nothing but its carbon footprint. Delicate ferns often leave nothing behind except this kind of carbon staining pattern.

Pseudo fossils —these are simply the track of water and minerals dissolved in them through other sediments. They look like plant or animal parts but are instead just the appearance of them.