Purpose

This lab will introduce you to a small portion of the wide variety of life preserved in the fossil record. You will learn to identify fossil organisms using a key based on easily observable morphological characteristics. You will also learn what an index fossil is and what index fossils are used for.

In the previous lab you learned about some of the processes that can result in the preservation of an organism as a fossil. Now that you know what fossils are and why they exist you can move on to learning how to identify them biologically. Geologists must be able to identify specific fossils in order to date geologic events, such as the time of deposition of a given sedimentary rock unit.

You may be familiar with the Linnaean system used to classify living things. This taxonomic scheme is a hierarchy. Each level, except the species level, can contain several subordinates. The species level is the most specific group to which an organism can belong. Biologists will tell you that members of a species appear morphologically similar and can interbreed, producing fertile offspring. Since geologists and paleontologists often deal with extinct organisms, the assumption must be made that fossils that look the same belong to the same species. The other requirements can not be tested. Here is an example of the Linnaean classification scheme applied to you:

Kingdom Animalia

An index fossil is an abundant and easily identifiable fossil with a wide geographic distribution and a short geologic range. The term geologic range refers to the total length of geologic time that an organism was, or has been, present on Earth. Index fossils, also known as guide fossils, are used by geologists to determine the ages of strata and to correlate rock units.