noun
: a fossil that is usually of narrow time range and wide spatial distribution and that is used in the identification of related geologic formations (as in locating new petroleum reserves)
noun
: a fossil that is usually of narrow time range and wide spatial distribution and that is used in the identification of related geologic formations (as in locating new petroleum reserves)
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012