What Are Microfossils?
As their name implies, microfossils are very small remains of organisms that require magnification for study. Collectively, they range in size from less .001 mm (1 micron), which is invisible to the naked eye, to the 1 mm size of a coarse sand grain, although some forms grow up to 20 cm. The latter are still referred to as microfossils because they belong to the same taxonomic group as the minute forms, and they also require microscopic study for identification. Whereas plants, invertebrates, and vertebrates are distinct taxonomic groups, the paleontologic subdiscipline of micropaleontology encompasses a heterogeneous array of minute fossils. They can be plant or animal, unicellular or multicellular, mineralized or organic, shells or skeletons, seeds or spores, teeth or jaws, or enigmatic forms of unknown affinity. Because they are so small, thousands of well-preserved specimens can be retrieved from a small sample of sediment or sedimentary rock.
Many of the commonly studied groups are unicellular, such as foraminifera, calcareous nannoplankton (e.g., coccolithophorids, discoasters), dinoflagellates, acritarchs, diatoms, and radiolarians. Others are microinvertebrates (e.g., ostracodes) or parts of macroinvertebrates (e.g., conodonts), reproductive bodies of plants (e.g., spores and pollen), or of uncertain affinity (e.g., chitinozoans -- Could they be the egg cases of the extinct group of invertebrates known as graptolites??).
My studies have been primarily on foraminifera, which are amoeboid-like marine organisms with calcareous or agglutinated shells of one or more chambers in a wide variety of arrangements. Most are in the size range of sand grains. Their fossil record begins near the base of the Cambrian Period (~542 million years ago). More than 40,000 species have been described in the scientific literature, and nearly 7000 are constituents of the modern marine biota. The micropaleontological slide shown below measures 7.62 cm (3 inches) across. On it are more than 300 specimens of fossil foraminifera extracted from a single sample and sorted according to species.
Below is the fossiliferous limestone tile that my wife selected when we were remodeling our bathroom. At the time, she didn't realize the shells were of Larger Foraminifera, which inhabit shallow tropical waters. The two largest specimens shown are nearly 2.5 cm (~1 inch) long; they look very different because one is oriented perpendicular to the other. Symbiotic algae within such forams enable them to grow rapidly and attain their large size.
An interesting historical footnote:
You can view some really neat scanning electron microscope (SEM) images of microfossils in my MicroGallery.
Micropaleontologists (scientists who study microfossils) are divided into two primary groups based on whether or not the remains they study are mineralized. This division is not taxonomic, but strictly for convenience as different laboratory processing methods are involved. Palynologists study organic-walled microfossils (e.g., dinoflagellates, acritarchs, chitinozoans, spores, and pollen), which are isolated from sedimentary rocks by using acids to dissolve the inorganics. The other micropaleontologists literally focus on phosphatic microfossils (e.g., conodonts), siliceous microfossils (e.g., diatoms, radiolarians, silicoflagellates), or calcareous microfossils (e.g., calcareous nannoplankton, calcareous algae, ostracodes). Although most of the Foraminifera are calcareous, this group includes many agglutinated forms conducive to the same processing methods.
There are numerous other kinds of microfossils that I have not mentioned, including archaeomonads, calciospores, calpionellids, chrysomonads, ebridians, microforaminifera, phtyoliths, prasinophycean algae, pteropods, scolecodonts, tentaculitids, and tintinnids. They are generally (but not always) less useful in biostratigraphic correlation because they are relatively rare or absent in most outcrops and boreholes. Microscopic elements of animals (e.g., sponge spicules, echinoid spines, fish teeth and scales) are common but of little diagnostic value. I also haven't mentioned microbes like bacteria, which are primarily of interest to those studying the Proterozoic biosphere. Sooner or later, I expect a specialist on one of these other groups to demand that I afford their favorites more attention and acclaim here!
Why Study Microfossils?
As a result of their abundance and diversity through time, microfossils have provided a tremendous amount of data that have advanced our understanding of Earth history and ecosystem dynamics. Studies on modern microbiotas (that we often prematurely but conveniently refer to also as "microfossils") enable us to better understand their counterparts that have been preserved in the sedimentary rock record for millions of years.
Several microfossil groups are particularly useful in biostratigraphic correlation, paleoenvironmental reconstruction, and paleoceanography. For much of the past century, micropaleontology served the petroleum industry as a primary tool for subsurface correlation of geologic layers, and this utility fostered a tremendous growth in the taxonomic, biostratigraphic, and paleoecologic aspects of this discipline. In the 1970s, much of the emphasis shifted to interpreting newly acquired deep-sea core sequences, which enabled refinement of the geologic time scale and brought paleoceanography to the forefront of scientific research. Subsequent chemical analyses of microfossils have revealed spatial and temporal variations in radioactive isotope ratios mirroring trends in the physical, chemical, and biological aspects of the global ecosystem, relevant to a diversity of topics such as plate tectonics and paleoclimatology. In addition to these relatively new frontiers, microfossils remain ideal subjects for studies on ecology and evolution. Modern forms have proven increasing useful in environmental monitoring of aquatic environments subject to urban and industrial pollution. Even forensic investigations have relied on micropaleontology! (Those diatoms in the mud tracked into the carpet in the suspect’s home prove that he was at the scene of the crime!)
Microfossil PublicationsListed below are publications that cover multiple kinds of microfossils. In addition, there are many other books and journals devoted to specific groups of microfossils. The best source for these are the libraries of major universities. If you're looking to purchase new/used/out-of-print books or the wall chart, try Amazon.com.
What does it take to become a paleontologist?
I'm frequently asked about this, especially by youngsters who have yet to realize there is a lot more to paleontology than just dinosaurs. As with any technical field, it takes a genuine interest in and devotion to the subject, and a lot of self-discipline and determination to successfully complete the required schooling. This is real science dominated by data gathering, analysis, documentation, and presentation. Hence, one must be detail-oriented and it is most beneficial to possess good oral and written communication skills. Most paleontologists have a graduate degree in geology with an emphasis in paleontology. In the United States, the overall job market for paleontologists (micropaleontologists in particular) has tightened over the past two decades, primarily due to the decline in domestic oil exploration and the mergers throughout the industry. Nevertheless, there are still hundreds of paleontologists working in academia, the petroleum and environmental industries, government agencies, public museums, and independent consulting firms. Others have transitioned into other kinds of geology or resumed their education toward highly marketable careers in fields like medicine and computer science. Opportunities continue to abound for those interested in teaching earth sciences at the high school or community college levels. For more information on careers in paleontology, informative brochures are available from the Paleontological Research Institution and The Paleontological Society.
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