| All these traits make an index fossil especially useful for rapid determination of the approximate age of an outcrop and its correlation in the field. |
| The index fossil concept allowed archaeologists to date sites relative to one another. |
| Ideally, an index fossil should be such as to guarantee that its presence in two separated rocks indicates their synchroneity. |
| One might use the identification of an index fossil in the field to extrapolate or to assume that the particular zone or assemblage was represented. |
| The greater the rate of evolution, the shorter the period of time represented by any given index fossil and the narrower the limits of relative age assigned to the rocks containing the index. |
| Because of its temporal restriction, Theodossia is a good index fossil and aids in the correlation of sometimes widely separated rock units. |
