| These fossils are indexes of relative geologic age and may be termed index fossils. |
| They are very abundant in some Paleozoic formations and include useful index fossils. |
| Ostracods—small crustaceans radiated during the Jurassic and are used today as index fossils. |
| Induan marine strata are correlated worldwide by six biozones containing ammonoid cephalopod index fossils. |
| Unfortunately, geochronologists assume that index fossils represent an absolute pattern. |
| These rocks are interbedded in Emsian marine sedimentary successions that are well documented by index fossils. |
