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Interpretations of Fossils

Interpretations of Fossils

Fossils, the remains of once-living organisms or their behavior, have long been known to human­kind, but interpreted differently depending on time and place. Since their first recorded discovery by ancient Greeks, Romans, and Native Americans, fossils have been explained as the remains of gods and giants, used to support notions of natural magic, treated as petrified organisms killed in Noah’s Flood, and ultimately regarded as some of the strongest evidence for Darwinian evolution. The scientific study of fossils began in the 16th century and has changed dramatically, depending on the prevailing views of the scientific community and the technology available to researchers. Today, the science of is a vibrant discipline strongly integrated with , biology, chemis­try, and other sciences.

Although fossils were discovered and often interpreted by the ancient Greeks, Romans, and Native Americans, the first rigorous and system­atic studies of fossils were carried out by 16th- century European naturalists. To these naturalists, the word referred to a range of natural curi­osities dug from the , including stones, gems, and the remains of once-living organisms that comprise today’s concept of fossils. Early natural­ists, however, had a difficult time recognizing the organic nature of fossils, due both to philosophical constraints and to the very practical difficulty of identifying often fragmentary and eroded speci­mens. Several encyclopedic works, including Georg Bauer’s (1494-1555) On the Nature of Fossils and Conrad Gesner’s (1516-1565) On Fossil Objects, recognized the extraordinary similarity between some fossils and living organisms, but were hesi­tant to describe these specimens as the remains of once-living creatures. Instead, many naturalists of the time considered fossils to be the result of natu­ral magic or a “plastic force” that could reproduce the shapes of common objects in situ in solid rock. These views were tied into an overarching natural philosophy that saw the world as a harmonious and interlocking web of affinities, guided by super­natural powers.

Although often hinted at by philosophers (includ­ing Xenophanes of Colophon and Leonardo da Vinci), the organic nature of fossils was first rigor­ously demonstrated by Nicolaus Steno (1638­1687), a Danish anatomist and crystallographer. In dissecting the head of a giant shark that washed up near Livorno, Steno noticed an uncanny resem­blance between the creature’s teeth and glossope- trae, a type of odd stone common on Malta that was thought to have curative and magical powers. While others had previously noted the resemblance, they were at a loss to explain how petrified sharks’ teeth were found on land, often on mountains thousands of feet above sea level. Noting that glossopetrae resembled a modern shark tooth in every respect, Steno wrote that these stones must be the remains of once-living organisms, a conclusion he generalized to other fossils that resembled living creatures or their organs, such as bones, shells, and leaves. This conclusion was strongly supported by early microscopist Robert Hooke (1635-1703), who used this new instrument to examine the microscopic composition of fossils, which he found to be nearly identical to the microstructure of the living organisms they resembled.

With the organic nature of fossils now secure, most researchers at the time regarded fossils and their entombing rocks as products of Noah’s Flood. However, based on field excursions in Tuscany, Steno recognized that rocks are found in layers made of different materials, which he hypothesized as representing a sequence of different events in the history of the earth. The notion of sequential peri­ods in earth history was supported by noted French anatomist Georges Cuvier (1769-1832), whose careful comparisons of fossil sloth and elephant specimens to their modern counterparts recognized the former as distinct species. By now, exploration of the New World made it implausible that these fossil species would be found alive in an unex­plored corner of the globe, indicating to Cuvier that they must have gone extinct. Up until this point, early naturalists such as Martin Lister (c. 1638-1712) and John Ray (1627-1705) regarded extinction as impossible, as it would imply imper­fection in God’s creation. To Cuvier, the reality of extinction suggested that earth history could be divided into distinct periods punctuated by “revo­lutions,” an idea that soon found support in the geological fieldwork of Jean-Andre De Luc (1727­1817). Furthermore, Cuvier himself carefully stud­ied the thick rock sequences exposed in the gypsum quarries at Montmartre, and found evidence of several very different faunas of fossil mammals, which gradually became increasingly differentiated from modern faunas further back in time. Additional exploration, especially in Great Britain, revealed several distinct periods in geological history, includ­ing an era dominated by reptiles (dinosaurs, plesio­saurs, ichthyosaurs, etc.).

Cuvier roundly denied the possibility of evolu­tion, but his research and that of others conclu­sively demonstrated that new species must have arisen over time to explain the distinct new faunas appearing after his “revolutions.” At the same time, James Hutton (1726-1797) and Charles Lyell (1797-1875) provided decisive evidence that the Earth was ancient, not several thousand years old as theorized by Biblical scholars. Although most of his argument focused on living species and selective breeding, Charles Darwin (1809-1882) used evidence of distinctive faunas and an ancient Earth to argue for the reality of evolution by natu­ral selection. Two years after the publication of Darwin’s On the Origin of Species (1859), the discovery of the Jurassic bird Archaeopteryx in Germany provided the first convincing “missing link,” as its combination of reptilian (teeth and a long tail) and avian (feathers and wings) features indicated an evolutionary transition between these two groups. In the following decades, a nearly complete assemblage of horse fossils from the newly opened American West was used by Thomas Henry Huxley (1825-1895) and O. C. Marsh (1831-1899) to illustrate gradual progressive evo­lution over time. Additional discoveries by Marsh, including several toothed Cretaceous birds, revealed the early evolutionary history of living animal groups. From the time of Darwin, Huxley, and Marsh to the present day, fossils have been interpreted in an exclusively evolutionary context, and continue to help scientists understand the pat­terns and processes of evolution. The recent hypothesis of punctuated equilibrium, which pos­tulates that longtime evolutionary stasis is punctu­ated by rapid speciation, was supported with careful study of extensive trilobite fossil faunas from the eastern United States.

Today, the science of paleontology is a dynamic and vibrant discipline that is becoming increasingly integrated with other fields of research. The discov­ery, preparation, and study of fossils are constantly changing with the development of new technology, such as molecular DNA analysis and CT scanning. The philosophical framework of paleontology has changed as well, and cladistic methodology is rou­tinely used to study the genealogical relationships of organisms, and sophisticated statistical tech­niques are used to examine patterns of evolution. As is evident from its history, paleontology will continue to change over time with the development of new research methods, new technology, and new scientific philosophy.

Stephen L. Brusatte

See also Archaeopteryx; Darwin, Charles; Dinosaurs; Evolution, Organic; Fossil Record; Geologic Column; Hutton, James; Huxley, Thomas Henry; Lyell, Charles; Paleontology; Steno, Nicolaus; Stromatolites; Trilobites; Xenophanes

 

Further Readings

Mayor, A. (2000). The first fossil hunters: Paleontology in Greek and Roman times. Princeton, NJ: Princeton University Press.

Rudwick, M. J. S. (1976). The meaning of fossils: Episodes in the history of palaeontology. Chicago: University of Chicago Press.

Ruse, M. (2000). The evolution wars: A guide to the debates. Santa Barbara, CA: ABC-CLIO.

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