Fossils are the remains or traces of once living organisms. Our introduction to paleontology (the study of fossils), will be limited to those forms that are commonly preserved and geologically useful. For Historical Geology purposes, we will be concerned with two aspects of paleontology: (1) fossils as indicators of relative age (using the Principle of Floral and Faunal Succession. fossils as indicators of environment. All organisms are dependent on their environments for survival. Some organisms, however, can survive only in restricted environments. Consequently, we can apply the principle of uniformitarianism to fossils to interpret the environment in which they lived. Modern fish, for example, tend to live in water. Ancient fish, then, probably lived in water as well. We will divide the environments into two basic categories-- the terrestrial (land-based) environment, and the marine (ocean) environment. Because marine fossils are most commonly preserved, the marine environments are shown in figure1.
Shallow marine bottom-dwelling organisms such as corals represent the benthic environment. Similarly, some species of fish indicate the neritic environment (the shallow seas covering the continental shelves). Other organisms such as radiolarians and some diatoms are characteristic of the oceanic or deep ocean environment. Still other organisms inhabit the ocean in both the neritic and oceanic areas and simply suggest a pelagic environment.
Marine fossils can be further described in terms of their life habits. These habits are shown in Figure A2. Corals, for example tend to be attached to the bottom and are thus referred to as benthic (bottom dwelling) sessile (fixed). Lobsters, however, move along the ocean bottom and although still benthic, are also considered vagrant. Swimming and floating organisms are referred to as nektonic and planktonic, respectively. In our example above, some fish might represent the nektonic pelagic environment.