276 -- Determination of Age of Ilymatogyra arietina, Ostera, Cretaceous of Texas, Through Counting of Growth Lines

Our group hypothesized that by counting the growth lines on Ilymatogyra arietina, an extinct oyster species from the Cretaceous, we could determine an accurate age of each oyster in question. We examined four specimens of this species using the assumption that the wider growth line sets represented annual growth while the thinner, less pronounced lines represented monthly growth sets. On average, there were twelve thinner growth line sets within each thicker growth line set. Using this as our proxy, we counted all the growth lines visible at 100x and 400x magnification on specimens utilizing a dissecting microscope and scanning electron microscope. Total growth lines were divided by twelve to determine an age in years for each specimen. Using this method, we determined our specimen set to contain oysters ranging from 2.5-4.5 years old, comparable to the modern oyster Crassostrea virginica (Atlantic Oyster), which have a lifespan anywhere from 6-15 years. Our Ilymatogyra arietina specimens were all within 1 cm, so a larger sample size would help determine a broader range of the species average life span.