A method in which species of plants and animals are used to indicate a feature of the environment. If the modern environmental requirements are known, the presence of preserved remains of the same species in ancient deposits and soils may suggest that similar conditions prevailed in the past. Many such indicator fossils are used to reconstruct temperature. However, the absence of an environmental indicator does not imply lack of the conditions which it is supposed to indicate. The method is only reliable when whole communities, comprising many different species, all indicate the existence of a particular environment.