Research Training Program

Julia Brown
Vanderbilt University
Nashville, Tennessee

Gene Hunt, Ph.D.
Supervising Scientist
Department of Paleobiology

"My research on deep sea ostracodes has provided me with a chance to study organisms that lived millions of years ago, and has given me a new perspective on time and the history of life."

Did Deep Sea Ostracodes Get Bigger?

A wide variety of organisms display a phenomenon known as Cope's Rule, which is a general tendency of body size to increase over time. However, the mechanisms behind this evolutionary trend are poorly understood. Ostracodes are small bivalve crustaceans, well represented in the fossil record, that appear to exemplify Cope's Rule. Preliminary studies indicated that increases in body size in the ostracode genus Poseidonamicus occur at the same time as decreases in deep-sea temperatures during the Cenozoic. Essentially, ostracodes appear to become larger as the climate cools. This finding relates Cope's Rule to the equally notable Bergmann's Rule: organisms in colder climates will be larger than those in warmer climates. This project followed up the initial studies on ostracode body size, and examined sixteen ostracode populations from two sites on the Indian Ocean floor to see if the same pattern appeared across additional sites and species. Ostracode body size was measured and charted over time, using samples ranging from 40 million years ago until about one million years ago, to investigate any correlations between body size and paleotemperature estimates, and elucidate the mechanisms underlying Cope's Rule. An overall increase in ostracode body size was found as global deep-sea temperatures decreased over time. However, especially on shorter time scales, the patterns of body size evolution appear to differ significantly between different species and sites. This indicates that although a cooling global climate seems to be driving the general trend toward increasing body size in deep sea ostracodes, there are many other local and species-specific factors capable of influencing body size evolution.

This research was supported by a grant from the William A and Nancy F. McMinn Scholarship.

Letter of gratitude