Paleoecology and Taphonomy of Some Eurypterid-bearing Horizons in the Finger Lakes Region of New York State
Stephen M. Mayer
This news article was summarized by Alexander Favaro. Alexander Favaro is a first-generation student attending the University of South Florida, pursuing a B.S. in Geology. He hopes to follow his passion of being a paleobiologist. His interests have been broadly focused on paleoecology and understanding evolutionary trends.
What data were used? The study used well-preserved fossils from the upper Silurian Fiddlers Green Formation in New York, the Lower Devonian Olney Member in Finger Lakes New York, Split Rock Quarry near Syracuse New York, and the Samuel J. Ciurca Eurypterid Collection at Yale Peabody Museum of Natural History. These data were used to make interpretations of eurypterid lifestyles and processes of fossilization.
Methods: Sedimentological variables and the body and trace fossils found within a rock unit were used to interpret the depositional environment (what type of environment the rocks were formed in) of a formation. Field collection was done at the Phelps Member and Cayuga Junction (which are located in the Fiddlers Green Formation), as well as Split Rock Quarry in Syracuse, New York. The Yale Peabody Museum of Natural History was used to supplement eurypterid data through their collection. The position in which each eurypterid was found, as well as their size, was used to describe their age, ecology, and how they likely died.
Results: Many eurypterid exuviae (shed exoskeleton) were found, while eurypterid bodies were less abundant. The most common eurypterid fossils found in Phelps were Eurypterus remipes. Cayuga Junction also possessed Eurypterus remipes but were far less common. At Split Rock Quarry, Erieopterus microphthalmus were found in localized calcareous (chalky limestone) bands.
The study found that between 61 carapaces, the average size of eurypterids in the Phelps Member fell between 15-25mm. The variations in size indicated that immature species and adults were living amongst each other.
Since eurypterids were chelicerate arthropods (like arachnids, sea spiders, and horseshoe crabs), scientists have suggested that eurypterids would undergo a group spawning and then molt (shed their exoskeleton) together (similarly to a horseshoe crab). This would explain the high number of shed exuviae and variable size ranges found in the formations.
Fossil evidence indicated that eurypterid corpses were highly affected by currents, which would cause a variety of contortions in a carcass. The observed eurypterid corpse conditions were categorized as: a non-contorted corpse, an angular contortion up to 900, a U-shaped flexure of the body and tail (as seen in Figure 1), and a contortion where the body and tail flipped above or below the head (though this was rare). Aside from flexure of the body, some contortions were caused by sediment that anchored a section of the eurypterid while the un-covered portions moved freely due to current movement. Eurypterus remipes and Erieopterus microphthalmus both displayed similar contortions and so they were able to determine that the contortion patterns weren’t exclusive to one genus of eurypterid.
Why is this study important? The study gave insight into the life and death of a once thriving taxon that has close relatives still alive today in the form of arachnids, sea spiders, and horseshoe crabs. Fossil evidence at Phelps suggested that eurypterids may have mass-molted, similarly to horseshoe crabs. The paleoecological evidence found gave a key insight into a behavior which has also been observed in modern, related organisms.
The big picture: The analysis performed on both trace fossils and carcasses gave both paleoecological and taphonomic (how an organism is fossilized after death) insight. Combined, taphonomy and paleoecology provides a more refined idea of how ancient organisms lived, died, and how their bodies would have been fossilized.
Citation: Mayer, S. M. Paleoecology and Taphonomy of Some Eurypterid-Bearing Horizons in the Finger Lakes Region of New York State.