HOW DOES BODY SIZE AND ABUNDANCE OF TRILOBITES CHANGE ALONG A WATER DEPTH GRADIENT IN THE TRENTON GROUP (MIDDLE ORDOVICIAN) OF CENTRAL NEW YORK?

Body size of organisms is a significant characteristic associated with metabolic rate, extinction, and other ecological and evolutionary traits. Body size has also been linked to species abundance; the number of individuals supported by an environment is limited due to resource allocation. The Middle Ordovician Trenton Group located in central New York represents deposition of shallow-shelf carbonates to deep-water shales within the Taconic foreland basin. Cisne and Rabe (1978) determined that the Trenton Group fossil communities were distributed along a water depth gradient. Other environmental factors change in conjunction with water depth and influence the distribution of fauna that live along the sea floor. The trilobite Flexicalymene is found throughout the Trenton Group but is restricted to shallower water relative to Triarthrus, a deep-water genus (Cisne et al., 1980; 1982). It is unknown whether there is a difference in body size between the two genera along the gradient. In order to investigate if trilobite body-size distribution changes along the gradient, we will test the hypothesis that there is a greater abundance of the smaller-bodied trilobite species on the deeper part of the Taconic Basin. Trilobite specimens will be measured from the Cisne collections, currently housed at the Paleontological Research Institution (Ithaca, NY). Cephalon length and width measurements will be measured using ImageJ. The cephalon length will be used as a proxy for body size (Trammer and Kaim, 1997).

Abundance data will be obtained from the personal notes of John Cisne. It is expected that a greater abundance of smaller Triarthrus fossils will dominate the deeper portion of the Taconic basin, while the larger Flexicalymene fossils will be more abundant in shallow areas of the basin. The findings of this study will provide information on trilobite body-size distribution to help elucidate environmental factors within the Taconic foreland basin.

Keyword: Flexicalymene, Triarthrus, resources, cephalon, Taconic