Virtual Field Study
How do you Quantify Change?
Do two fossils with slightly different morphology collected from a sequence of rocks represent evolutionary change? This section of the module addresses this question by engaging you in the process of quantifying and examining data and then using that data to validate or reject an inferred evolutionary relationship. In order to examine how morphologic variables have changed over time we need a way to quantify them. Paleontologists often need to measure dozens of different parameters in a fossil before they find one that seems to change over time. Dr. Patricia Kelley, whose data set we are using, determined after thousands of measurements that for the bivalves Astarte and Anadara, two variables - internal volume of the shell and shell thickness- showed change over time. How do you measure the internal volume of a bivalve? How do you measure shell thickness? This part of module will take you inside the laboratory, where you will learn how field data is quantified, graphed, and examined. Critical examination is necessary in order to determine whether the trends in the data show evolutionary change or a reversible response to changing conditions ("morphologic plasticity").
Click on the photograph for a video demonstrating a geologist quantifying collected shell data!
Last modified October 06 2008 03:14 PM