Species of plants and animals that 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. Ivy is a well-known example: this plant is particularly susceptible to hard winters and autumn frosts, and is today restricted to areas of moderately high summer temperature and average temperature in the coldest winter month above —1.5°C; the appearance of ivy in a pollen diagram is thus often taken to be evidence of an amelioration of climate. There are, however, pitfalls with these methods. Many other factors of ecology may also exert control over the distribution of a species, and the absence of an environmental indicator does not imply lack of the conditions which it is supposed to indicate. In addition, the ecology of the species may have changed. The method only becomes reliable when whole communities, comprising many different species, all indicate the existence of a particular environment.
The Macmillan dictionary of archaeology, Ruth D. Whitehouse, 1983Copied