March 2002 Meeting Abstract
Eurypterids were arthropods that lived through much of the Paleozoic Era, reaching their peak in diversity during the Late Silurian and Early Devonian. The eurypterid body includes a prosoma, bearing eyes and six pairs of appendages, followed by an abdomen consisting of twelve movable segments and a posterior telson. Studies of how the animals lived are often based on comparison with their closest living relative, the horseshoe crab. This analogue appears to provide valuable insights for some of the more generalized types of eurypterids, suggesting lives spent sorting through sediments in search of worms. Other, co-occurring types, however, exhibit a variety of features suggesting lives as well-adapted, active predators. Although eurypterid fossils have been found at localities on several continents, their occurrences in the Upper Silurian Bertie Group exposed across much of New York State and Ontario are among the best known. This deposit is a classic Lagerstaette, in which not only minute detail but also original organic skeletal material is commonly pre-served. Although numerous complete eurypterids were preserved by this process, their discovery and subsequent excavation requires diligent search and effort. The number and identity of eurypterid species in the Bertie Group has been a subject of controversy for several reasons, including disagreements between "lumpers" and "splitters." For example, Eurypterus remipes, the official "New York State Fossil," and Eurypterus lacustris are still considered by various workers as either separate species, subspecies of each other, or even synonyms. Part of the confusion appears to have arisen from the old separation of Bertie Group eurypterids into two geographic localities or "pools," the "Buffalo Pool" including E. lacustris and several other species characteristic of western New York and adjacent Canada, and the "Herkimer Pool" of East Central New York with E. remipes and other species similar to those in the "Buffalo Pool." These two "pools" were thought to have existed contemporaneously, separated by some barrier, but subsequent work has demonstrated that the "Herkimer Pool" eurypterids consistently occur in rocks (Fiddlers Green Formation) that are older than those (Williamsville Formation) of the "Buffalo Pool." This presentation focuses on an investigation of the occurrence of eurypterids from the latter.
Relatively little is known about the environment in which the Bertie Group eurypterids lived. The absence of fossils of organisms typical of normal marine conditions (corals, bryozoans, most brachio-pods, bivalves, trilobites, echinoderms) suggests that they lived in waters that were not of normal salinity. Recent studies of the rocks themselves have indicated that the eurypterid-bearing deposits represent tidal flats or even a supratidal sabkha-type environment similar to that found in places along the edges of the Persian Gulf today. The eurypterids would have lived offshore, with their remains being trans-ported into these environments during storms. Most, if not all, fossil specimens appear to represent cast-off moults or parts of moults. The remains were concentrated in long, shallow depressions ("windrows") oriented parallel to shore, with the result that eurypterid fossils tend to be found in clusters separated by wide expanses of equivalent rock that is relatively barren. An examination of the orientations of complete or nearly complete individuals indicates a prevalence of specimens that were flipped onto their backs, with evidence of size sorting and alignment. Accumulations of modern horseshoe crab remains on tidal flats today show similar patterns. Even though complete eurypterids were commonly preserved, most fossils found are of partial specimens or isolated parts, and one often wonders how large the eurypterid was that had a particular part preserved as a fossil. A local secondary schoolteacher developed an exercise for her students in which they would measure actual fossil specimens of eurypterid parts and then by comparison to a picture of a complete individual use proportions to determine the size of the eurypterids with those parts.Dr. Batt developed a version of this exercise using image processing techniques, where digital pictures of fossils of eurypterid parts can be measured and compared to a picture of a complete individual using a program such as Image J. This procedure allows size determinations of a large number of individuals in a short time without the need for teachers to have access to actual specimens. The data can then be used to generate histograms showing size frequency distributions of the eurypterids within a population. It is even possible to recognize breaks in these distributions that may represent molting stages.
Dr. Batt holds a Bachelor's degree from SUNY Buffalo, a Master's in micropaleontology from the University of Wyoming, a Ph.D. in paleontology from the University of Colorado, and a second Master's in hydrogeology from Western Michigan University. He has been teaching at Buffalo State College since 1989. His major research interests include studies of ammonite paleoecology using shell morphotypes, delineation of small-scale cyclic sea-level fluctuations recorded in Middle Devonian Hamilton Group shale sequences using faunal dominance trends, eurypterid paleoecology and occurrences, and malachology (the study of modern mollusks and their shells). He is also involved in Science Education, in particular the use of dinosaur science by teachers to spark interest in science and an understanding of the nature of science among K-12 students, and has made several presentations on this topic at Science Education conferences. He also assists his wife, science education professor Dr. Robin Harris, in her work with the Buffalo Science Teachers Network and other endeavors by serving as a geology content advisor.
With the Annual Gem and Mineral show right around the corner (March 23 and 24, 2002), it will be great to refresh our knowledge on eurypterids. So, I am inviting you to join us in attending Dr. Batt's presentation and to bring along your own prize specimens to the meeting and show them off. Please note that the venue has changed this month: We are meeting at Eddie Ryan's Restaurant located on Central Avenue in the Village of Lancaster.
See you there.
Lea Cervi
Executive VP