A NEW EURYPTERID LAGERSTäTTE FROM THE UPPER SILURIAN OF PENNSYLVANIA

Eurypterids are generally rare in the fossil record but they occasionally occur in mass assemblages. The genus Eurypterus is well known to occur in abundance in the Upper Silurian formations of the northern Appalachian Basin (New York and Ontario), but is uncommon in the central Appalachian Basin. The recent discovery of an exceptionally preserved mass assemblage of Eurypterus flintstonensis molts in the Tonoloway Formation (Pridolian) of Pennsylvania offers new information on the behavior, life habitat and systematics of this rare, poorly described species. It also provides new paleoecological data for the Tonoloway Formation in this region.

The previous description of E. flintstonensis was based on isolated and fragmentary material from the Tonoloway Formation of West Virginia. In the Tonoloway Formation of Pennsylvania, although specimens are predominantly disarticulated and fragmentary, several fully articulated, exceptionally preserved eurypterids are present. Eurypterids in this location are found in calcareous shale, most likely deposited within the intertidal zone of a shallow carbonate ramp. The absence of carcasses and the presence of putative trackways suggest that E. flintstonensis may have molted en masse in the vicinity of the burial site, whereupon molts were buried while the eurypterids migrated back to their normal life habitat. Additionally, preservation of small, juvenile-sized instars indicates proximity to a nursery or breeding ground. Limited faunal diversity and the presence of euryhaline organisms including ostracods and gastropods suggest a depositional environment with variable salinity; potentially hypersaline at times. Ongoing work aims to correlate the Tonoloway Formation of Pennsylvania with other locations in Pennsylvania known to yield eurypterids, while examining the systematics of E. flintstonensis and its relation to more common members of that genus including Eurypterus remipes and Eurypterus lacustris.