Paleontology

Paleontology is a broad field of study that focuses on the history of life on Earth. Fossils, which are the material remains (bones, teeth, shells) or traces (physical or chemical) of ancient organisms are what paleontologists study.

Fossils of single-celled organisms are known from rocks approximately 3.5 billion years old, and chemical traces of life (carbon isotopes of presumed biological origin) may extend even further back in time. It is an undeniable fact that the fossil record is an incomplete archive of the history of life, and this is especially true for organisms with poor preservation potential, such as soft-bodied worms and jellyfish. However, the quality of the fossil record is surprisingly good for those animals with durable skeletons, such as brachiopods, trilobites, mollusks, and vertebrates.

Many subfields fall under the broad heading of paleontology. The ma­jority of modern paleontologists focus their efforts on describing fossils and deciphering evolutionary history, or phylogeny. These “paleobiologists” tend to specialize on particular groups of fossil organisms, such as single­celled prokaryotes or eukaryotes, plants, invertebrates, or vertebrates. Through their efforts scientists gain a deeper understanding of life’s evolu­tion and diversification through time. Scientists also gain a better appreci­ation of the evolutionary process, because the fossil record provides the long-term record of evolution in action. Indeed, proposed modes of evolu tionary change, such as phyletic gradualism and punctuated equilibrium,

are based on patterns derived directly from the fossil record.

Another active branch of paleontological research is paleoecology, which is the study of the relationships and interactions between fossil organisms and their paleoenvironments. Paleontologists engaged in paleoecological re­search might focus their efforts on a single taxon. For example, a paleon­tologist may choose to study the predatory activities of a particular fossil snail by tracking distinctive traces of its predation (borings) in associated fossil bivalve shells. Another paleontologist may examine the fossilized leaves and woody tissues of ancient trees in order to identify diagnostic traces of a fossil insect that made its living within the tissues of the extinct plant. Still another may study the contents of fossilized feces (called coprolites) in or­der to decipher the dietary preferences and digestive capabilities of an ex­tinct species of dinosaur. On a larger scale, paleontologists may choose to track ecological changes in entire communities through time. A prime ex­ample of this type of paleoecological research would be the analysis of an­cient plant communities in response to long-term climate change.

Yet another contemporary field within the realm of paleontological re­search is taphonomy, which is the study of how organic remains are incor­porated into the rock record. Taphonomic analyses focus on the post-mortem history of biological remains, such as decay, disarticulation (separation of body parts), transport (perhaps out of life habitat), and bur­ial. Taphonomic studies can reveal important trends and biases in the fos­sil record, which must be recognized in order to produce accurate paleoecological and evolutionary reconstructions. At the most basic level, taphonomy points out that the scarcity of soft-bodied creatures in the fos­sil record is not due to scarcity of the original organisms, but to the poor preservation of soft body parts.

Finally, many paleontologists today are engaged in research directly re­lated to the phenomenon of mass extinction, which unfortunately is also a contemporary environmental issue. By tracking the record of extinction through time, paleontologists can provide unique insights into the poten­tial agents that cause the decimation of entire ecosystems on a global scale, such as extraterrestrial impacts. They can also gain an appreciation for the timing and nature of biotic recovery after major extinction events.

References

Briggs, D. E. G., and P. R. Crowther, eds. Paleobiology: A Synthesis. Oxford, England: Blackwell Scientific Publications, 1990.