Paleontology

Paleontology (from Greek: palaeo, “old, ancient”; on, “being”; and logos, “speech, thought”) is the study of ancient life. Life appeared on Earth about 3,550 million years ago in the oceans, subsequently evolved from simple bacteria-like cells to complex multicellular forms, and colonized the land. Countless adaptations resulted in a great diversity of biological forms and in addition changed the planet itself. We have learned about extinct organisms through the examination of fossils, the visible evidences left behind by them and preserved in rocks and sediments. Fossils include mineralized, carbonized, mummified, and frozen remains of bodies after death, or of cast-off parts, normally of the skeleton or portions, such as teeth, that became partially mineralized during life; the preservation of soft tissues, however, is extremely rare. Many other fossils consist of casts or impressions, tracks, burrows, fossilized feces (coprolites), as well as chemical residues.

People have collected fossils ever since recorded history began, and probably before that, but the nature of fossils and their relationship to life in the past became better understood during the modern era as a part of the changes in natural philosophy that occurred during the 17th and 18th centuries. The emergence of paleontology, in association with comparative anatomy, as a scientific discipline occurred at the end of the 18th century, when Georges Cuvier clearly demonstrated that fossils were left behind by species that had become extinct. Paleontology therefore is the study of fossils throughout geological time. The totality of fossils, both discovered and undiscovered, and their placement in sedimentary layers or strata is known as the fossil record. The fossil record ranges in age from the Holocene, the most recent geological epoch that began 12,000 years ago and continues until present, to the Archean eon, which extends from about 3.8 to 2.5 billion years ago.

Fossils vary in size from the microscopic (micro-fossils), such as fossilized shells of unicellular organisms, to those of gigantic proportions, such as the fossil bones of dinosaurs. Micropaleontology studies microscopic fossils, including organic-walled microfossils, the study of which is called palynology. The study of microfossils requires a variety of physical and chemical laboratory techniques to extract them from rocks and the use of light or electron microscopy to observe them. Macrofossils are usually studied with the naked eye or under low-power magnification, but the observation of fine skeletal details often needs high-powered magnification.

The study of macrofossils is undertaken by several specialties. Invertebrate paleontology deals with fossils of animals with no vertebral column, while vertebrate paleontology deals with those of animals with a vertebral column, including fossil hominids (paleoanthropology). Paleobotany undertakes the study of macrofossils of plants. There are many developing specialties, such as paleoichnol-ogy (the study of trace fossils), molecular paleontology (the study of chemical fossils or biomarkers), and isotope paleontology (the study of the isotopic composition of fossils).

Two of the most important portions of knowledge that paleontologists obtain from fossils include first how they were formed (taphonomy), that is, the process of fossilization through which some material or information was incorporated from the biosphere to the lithosphère; and second, what the organisms were that produced them (paleobiology), as well as how and where they lived and what their evolutionary history was. The [Page 958]source information for this purpose is the biology and ecology of present-day organisms, applying the uniformitarian principle. Fossils usually contain morphological information that allows us to recognize most of them as living organisms and then to identify and classify them according to the Linnaean taxonomy, as well as to study their relationships to other taxa.

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