1. Index fossils Some fossils are typical at a particular time segment. Useful in identifying the relative age of the rock in which they occur. Help us to identify geologic time periods. Four characteristics: 1. Must be easily recognized - Unique 2. Widespread in occurrence 3. Limited in time- existed for a brief period of time 4. Abundant AUWB!!!! A______ u________ w_____ b______

2. Eurypterid (Sea scorpion) of the Silurian Period

3. Example Fossil Assemblage One Oldest to Youngest: Cephalopod- Ordivician Blastoid – Mississippian Echinoid – Cretaceous Brachiopod – Pennsylvanian Pelecypod – Quaternary 2a) No, they are not in order 2b) Periods missing – Silurian, Devonian, Permian, Triassic, Jurassic, Tertiary

4. Repeat this for the remaining 3 assemblages and answer analysis and conclusion questions