ave

Finding the "Average"

Because of the effects of ontogeny (age relationships) or sexual dimorphism (sex differences) in fossils, paleontologists need to correct for these effects before looking for morphologic change over time. Dr. Kelley had to develop a statistical technique to average the data to eliminate these potential effects and she did so by calculating a mean shell length from each stratigraphic horizon. Dr. Kelley then took the mean of those means to obtaining one mean length per genus over time, or a "reference length." Deviations from this average length were plotted as a function of age (stratigraphic horizon) from which Dr. Kelley was able to track the magnitude of changing shell characteristics over time.

Part A: Dtermining the deviation
from average shell lenght per
depositional bed.

Part B: Ploting those deviations
against the complete section, to
determine how these devidations
have changed over time.

Back | Home | Next