Below are descriptions of recent research areas.
Eurypterid Paleoecology
Eurypterids are marine arthropods that are closely related to modern scorpions, and more distantly related to horseshoe crabs. They are an interesting group for several reasons: they were one of the first organisms to venture onto land; one genus was the largest arthropod ever; and they moved from marine to freshwater environments over their history. However, despite extensive study since the 1800s, certain basic questions about eurypterid ecology have remained unanswered. For example, we still know very little about the habitat preference of different eurypterid groups, or why they moved into freshwater environments.
My graduate research addressed the paleoecology of Paleozoic eurypterid arthropods in the mid-Paleozoic (Silurian – Devonian) of the Appalachian basin of North America (roughly, upstate New York to West Virginia), and their occurrence in marginal, sometimes extremely salty marine environments. To better understand eurypterid habitats and their ecology in this region, I used a variety of specimen- and field-based methods, including quantitative paleoecological analysis, sequence stratigraphy, geometric morphometrics (shape analysis), and trace fossil analysis. Using these varied approaches, I have been able to shed new light on: 1) eurypterid salinity tolerance, 2) their preferred habitats, and 3) environmental factors that controlled their preservation in the fossil record. The results of this research may eventually help us answer some big questions like, Why did marine animals come onto land?
A molting eurypterid in the late Silurian (illustration by Emily Damstra, emilydamstra.com)
Cretaceous crabs paleoecology and chitin biogeochemistry
Chitin is a common biomolecule that is made by all arthropods and used to strengthen their exoskeletons. Chitin in the exoskeleton can also tell us about the animal’s diet and environment because this information is recorded in the stable isotopes of carbon and nitrogen that make up the chitin itself. Chitin is occasionally found preserved in the fossil record, but we still don’t know much about how its isotopic signal changes over time. I worked with collaborators at the University of Cincinnati to test the hypothesis that stable isotopes in fossil chitin can be used to tell us about past environments.
Focusing on extremely well-preserved ~70 million year-old crabs from the Upper Cretaceous Coon Creek Lagerstätte of Tennessee, I carried out an investigation that included different types of geochemical analysis, including bulk and compound-specific stable isotope, and Raman spectroscopy. Crabs living in marine environments usually have a stable isotope signature that reflect a diet composed of marine organic matter. However, through our research, we have found that the ancient crabs living in the Coon Creek environment were actually eating the remains of land plants, rather than marine foods. This indicates that the crabs (and associated fauna) were living closer to shore than previously thought. Although this is surprising, this finding actually fits with what we know about some marine crabs that live very near to land today. The results of this research are exciting because they indicate, for the first time, that ancient marine arthropod remains can retain biological isotope signals that can be used to reconstruct past environments.
A decapod crab and associated molluscs from the Coon Creek Formation of Tennessee.
Other projects:
Eurypterid swimming trace fossils
I have just finished a project describing the first known eurypterid swimming trace fossils. These traces were originally found by long-time eurypterid collector Samuel J. Ciurca, Jr. (Sam’s eurypterid website), and occur in the upper Silurian Williamsville Formation of Ontario and Tonoloway Formation of Pennsylvania.
Although it has long been assumed that eurypterids were capable of swimming (eurypterid literally means “broad wing”), we had little physical evidence for their swimming behavior other than from the morphology of the animals themselves. These trace fossils, which we named Arcuites bertiensis, provide strong evidence that common eurypterine eurypterids (such as Eurypterus, the New York State fossil) used their oar-like paddles to swim using a rowing motion, just like modern swimming insects such as water boatmen and diving beetles. In addition to providing the first unambiguous evidence for eurypterid swimming behavior, these trace fossils are also exciting because they provide additional evidence that eurypterids actually lived in the shallow marine environments where we find their molted remains (i.e., the remains were not washed in from somewhere else). From this, we can infer that eurypterids preferred normal or even lower salinity conditions, as opposed to environments with extreme salinity.
A new eurypterid genus from Belarus
I recently collaborated with Dmitry Plax (Belarusian National Technical University), James Lamsdell (West Virginia University), and Dmitry Barbikov (Republican Unitary Enterprise Production Amalgamation “Belaruskali”) to a new genus of Devonian eurypterid from Belarus (the first formally described eurypterid from this country). Aside from the phylogenetic implications of this new genus, there are important paleoenvironmental and taphonomic implications from its occurrence in the Pripyat Trough. The specimens were found on thin clay layers interbedded within massive evaporite (potash or potassium salt) beds, and we suggest that eurypterids may have been washed into a hypersaline basin environment following storms. The close proximity of at least one specimen to an evaporite layer (within millimeters) strongly suggests that these specimens were truly “brined” during or shortly after burial, which would be a highly unusual form of preservation in the fossil record. Further work needs to be done on the stratigraphy of this fascinating deposit to better understand the paleoenvironment.
Matt Vrazo 