Prof. Mohammad Gameil
Lab. 5
Index Fossils
Index fossils are fossils that have short range and wide geographic
distribution. These fossils are important in age determination and
correlation of rock strata. Each period in the geologic time scale has
its index fossils which are explained below.
I.
Fossils of the Paleozoic:
Trilobites
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Graptolites
Brachiopods
Rugose corals (solitary)
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Rugose corals (colonial)
Foraminifera (Fusulinids)
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Prof. Mohammad Gameil
II.
Fossils of the Mesozoic:
At the end of the Paleozoic a great mass extinction led to the
disappearance of many organisms. Trilobites and graptolites
became extinct, brachiopods decreased drastically. The
following fossils are the index fossils characteristic for that era.
Brachiopods (Jurassic)
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Ammonites (Jurassic – Cretaceous)
Rudists (Cretaceous)
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Prof. Mohammad Gameil
III. Fossils of the Cenozoic
The end of Mesozoic (Cretaceous) witnessed the fifth Mass
Extinction which led to the extinction of many organisms such
as ammonites, rudists and of course Dinosaurs. Other
organisms appeared including microfossils of Nummulites,
Alveolins, Diatoms and Nannoplanktons.
Genus: Nummulites (Eocene)
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Genus: Alveolina (Eocene)
Clypeaster (Miocene echinoids)
Genus Scutella (Miocene echinoids) Genus Astrangia (Pleistocene corals)
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