There are two main types of fossils: body and trace. Body fossils include everything that makes up the animal like bones or teeth. Trace fossils are fossils that prove animal activity and life from a specific time period; footprints are a common example of trace fossils. Because animals leave thousands of footprints over their lives but only one body, trace fossils are more common and are considered just as important when looking at the fossil record.
Trace fossils including footprints, burrows and fossilized feces provide scientists with a proof of life. These trace fossils show what activities animals from the past may have engaged in, which is something body fossils cannot do. Paleontologists use the trace fossils to help construct what the ancient environment was like and how the animals and plants within that environment may have interacted with one another.
In many cases figuring out what type of animal or plant left the trace fossil is next to impossible. Most plants and animals will not become fossils. The trace fossils cannot be connected to animals unless a body is found which can be matched to the trace fossil. Even with a body, it can be difficult to match a body fossil to a trace fossil with a great deal of accuracy.
The ethological system of classifying trace fossils focuses on the behavior the animal may have been demonstrating based on the trace fossil found. For example the category calichnia includes structures that were used for breeding purposes like nests and bee hive cells. There are 11 accepted categories in the Ethological classification system with many other categories considered as tentative. Tentative classes may be incorporated into any one or more accepted classes in most cases.
The Toponomic system of classifying trace fossils ignores the living organism that may have created the fossil and focuses on the casting medium, or type of rock, and where the fossil is located. Each fossil is classified on its location in the medium. For example, a trace fossil that has been filled in completely with sediment and is totally encased in the rock medium would be considered an endichnia type trace fossil.
