9: Fossils
Fossils are defined as any evidence of past life; for our purposes we will consider something to be a fossil if it is unusual in that it is either ancient or has been altered from its original form in a way that makes it more likely to be preserved. Fossils are very important because they tell us about how organisms changed and evolved through time, how they interacted with each other and their environment, and how Earth’s climate and environments have changed through time.
- List the major types of fossils and modes of preservation
- Describe the morphology of fossils using the appropriate terminology
- Identify the major types of invertebrate body fossils in hand sample and thin section
- Identify the most common trace fossils and apply the ichnofacies concept to interpret depositional environments
Chapter thumbnail shows a fossil gastropod ( Masha Milshina via Wikimedia Commons ; CC BY-SA 4.0 ).
-
- 9.2: Types of Preservation
- Robust hard parts (teeth, bone, shell) and even soft parts (muscle, skin, other tissue) can be preserved. Replacement occurs when the original organic material is replaced with another material. Molds and casts are void and infills formed after organisms. Recrystallization occurs when a mineral changes to a more stable form. Carbonization happens when all the volatiles are driven off leaving only a carbon film. Permineralization occurs when mineral precipitate into void spaces.
-
- 9.4: Major Fossil-Forming Groups (Invertebrates)
- The overwhelming majority of fossils come from invertebrates that have hard skeletal material. The most common and easily recognized are sponges, corals, brachiopods, bryozoans, mollusks (bivalves, gastropods, and cephalopods), certain arthropods, and echinoderms.
-
- 9.6: Trace Fossils
- Trace fossils include tracks, trails, burrows, and any other fossilized behaviors. Trace fossils are named on the morphology of the feature, not on the interpreted trace maker. The ichnofacies concept groups associations of trace fossils together that likely record behaviors that worked in a particular environment.