Ichnofossil genera (currently in Atlas)
What are ichnofossils?
Organisms leave traces wherever they go, in the form of footprints, burros, and feces. When these traces become fossilized, they are then called ichnofossils. Ichnofossils preserve the behavior of organisms (animals and plants) in the form of tracks, trails, burrows, feces (or coprolite), and borings. Although they may preserve the outline or impression of an animal, ichnofossils are not composed of actual organism parts. Ichnofossils can be preserved on the substrate, directly in rock formations, or on other fossils, such as borings in corals. Ichnologists use ichnofossils to interpret past environments and conditions within the substrate, a task that is very important not only to paleontologists but to those working in the petroleum industry. Because the fossils are more important to interpret behaviors and environments, names of ichnofossil reflect the behavior, not the biological affinity, of the trace makers. Therefore, ichnofossils are categorized into ichnogenera based upon their appearance and behavior of the maker.
What is ichnology?
The study of trace fossils is called ichnology, and those that study ichnofossils are ichnologists. Ichnology can be considered a subdivision within paleontology, but the discipline actually lies in the realms of paleontology, biology, sedimentology, stratigraphy, pedology, and geomorphology. The study of modern organism behavior is called neoichnology. Several parallels can be made between ancient trace fossils and those from modern animals, thus giving ichnologists an idea of the type of behavior the organism performed to make the trace.
How do we identify ichnofossils?
Trace fossils can usually be distinguished based on geometric shapes, symmetry, or by unusual borings in other fossils. Some trace fossils can be hard to distinguish, as coprolites (fossil feces) and gastroliths (smoothed, rounded rocks from the gut of dinosaurs that helped in digestion) look like rocks or pebbles to the untrained eye. In the marine realms, such as the Late Ordovician, trace fossil are mostly identified as random boring patters on other fossils (Catellocaula, Trypanites), branching patterns that may be filled in with a different colored substrate (Chondrites), raised or indented snake-like patterns that may or may not be filled with sediment (Planolites, Phycodes), or by tracks (Cruziana) and imprints of the organisms as it burrowed into the sediment (Rusophycus).
What can ichnotaxa tell us about past environments?
Ichnofossils are studied mainly to document the behavior of past organisms, which can tell scientists something about the environment in which the organism lived. For example, if several ichnogenera, or ichnotaxa, are found within a particular formation, it can be interpreted that there were several different types of behaviors occurring simultaneously, which might mean that several different organisms lived within the area, indicating there might have been a lot of food and oxygen available to support a diverse community.
Over the years, ichnologists have created ichnofacies, with is a construct based on the identification of key features shared by an ichnocommunity (trace fossils that are associated with one another biologically) of a wide range of ages under a similar set of environmental conditions. Ichnofacies are commonly used in the petroleum industry to interpret what the environment of an area was like millions of years ago. However, the concepts are also important in all aspects of geology, as sometimes the only way to interpret if rocks were deposited in a freshwater or marine setting is to look at the ichnofossil assemblage and categorize that into an ichnofacies. This is just a single example, as there are numerous other ways that ichnofossils, ichnocommunities, and ichnofacies can be used within geology.