Index fossils

Index fossils

Index fossils (also known as guide fossils, indicator fossils, or dating fossils) are the fossilized remains or traces of particular plants or animals that are characteristic of a particular span of geologic time or environment, and can be used to identify and date the containing rocks. To be practical, index fossils must have a limited vertical time range, wide geographic distribution, and rapid evolutionary trends. Rock formations separated by great distances but containing the same index fossil species are thereby known to have both formed during the limited time that the species lived.