| A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time. |
| This extends the geographic range of this Gulf Coast index fossil west from Mississippi to Texas. |
| The index fossil concept allowed archaeologists to date sites relative to one another. |
| I even found a tiny index fossil the paleontologists said was really important. |
| 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 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. |
