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index fossil[′in‚deks ‚fäs·əl]
fossil remains of an organism that are typical of the sedimentary beds of a certain geological age and, therefore, are frequently used in identifying related beds from different regions. All index fossils are important in stratigraphy because they typically are of broad geographic distribution and narrow vertical distribution (because the organisms existed for a short time, they form relatively thin deposits). Their skeletons generally have specific characteristics in construction that make identification easy, even under field conditions.
Modern paleontology is based on the study of a whole set of fossil remains, not individual index fossils, because the use of index fossils as the only criterion in establishing the age of deposits may lead to erroneous conclusions. Nevertheless, index fossils are very useful for preliminary orientation in geological surveying, especially under field conditions.
V. N. SHIMANSKII