Paleontology
Paleontology is the study of the history of life as revealed in the fossil record. Fossils are remnants or traces of living organisms from past geologic ages that have become preserved in Earth's crust. They include not only the skeletons or shells of deceased creatures, but also burrows, footprints, eggs, and fossilized feces (excrement), known as coprolites.
Paleontology draws extensively from both biology and geology. Some subdisciplines of paleontology are defined by the types of organisms that are studied. Examples are vertebrate paleontology, invertebrate paleontology, paleobotany, and micropaleontology (study of single-celled fossils). Paleoecologists study extinct ecosystems. Related areas include biostratigraphy, the study of fossil distributions in different strata (rock layers), and taphonomy, which examines the process of fossil formation. Biological disciplines in which contributions of paleontology are particularly critical include systematics and taxonomy. They focus on determining phylogenetic relationships (the sequence of branching events in evolutionary history which have resulted in the production of divergent species) between extinct as well as extant organisms. Another such discipline is comparative anatomy, which examines the morphology (form) and structure of organisms. Still another is evolutionary biology, which examines how biological organisms change over time.
The study of the fossil record also permits the identification of periods of major change in biological diversity. Sudden shifts in flora and fauna result from major events involving the extinction of organisms, such as the one that eliminated the dinosaurs at the end of the Cretaceous period. In fact, geological eras are bounded by these sudden changes.
Taphonomy examines the processes by which fossils are formed. Any event that occurs between the death of an organism and its fossilization is of interest to taphonomists. The first step to fossilization is burial. Burial can occur in a number of ways; corpses may be buried by sediments in rivers, by sand, or in the bottoms of lakes or oceans. After burial, corpses may be compressed and distorted by the surrounding sediment. There is also a lengthy period of remineralization following burial. During this time, bone is replaced by minerals carried through the rock by water. Remineralization does not necessarily obscure fine detail because the replacement occurs on a minute scale.
During the process of fossilization, much information about the biology of organisms is lost. Damage to the corpse, either by scavengers or from weather or erosion, may occur prior to burial, and distortion from anumber of sources can occur afterwards. Soft parts of organisms are fossilized much less frequently than hard parts, and information on color, physiology, or behavior is particularly likely to be lost. It is because of the incompleteness of most fossils that paleontologists have developed a well-deserved reputation for inferring (deducing) huge amounts of information on the biology of organisms from fragmentary, or partial, remains.
The proper dating of fossil material is often critical to paleontological studies. Relative dating considers the relative placement of different rock strata; younger rock layers are formed on top of older layers. Also, similar sequences of strata that are found in different locations are likely to date from the same period. Absolute dates for fossil material are usually estimated using radioisotopes. This method makes use of the fact that radioactive atoms decay into more stable atoms at a known rate.
Fossil Record; Geological Time Scale; Paleontologist.
Bibliography
Futuyma, Douglas J. Evolutionary Biology, 3rd ed. Sunderland, MA: Sinauer Associates, 1998.
Gould, James L., and William T. Keeton. Biological Science, 6th ed. New York: W. W. Norton and Co., 1996.
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