Ecdysis in sea scorpions (Chelicerata: Eurypterida)

Recurrent patterns of disarticulation and dislocations of the eurypterid exoskeleton reflect biological processes and can be used to distinguish moults from carcases. This distinction is a prerequisite to understanding the palaeobiology of the Eurypterida. Taphonomic patterns indicate that eurypterid ecdysis was largely similar to that in Recent chelicerate orders, involving opening of sutures along the carapace margin and on ventral plates prior to emergence anteriorly. The diverse morphology of eurypterids resulted in a range of constrictions or ‘bottlenecks’ in the exoskeleton through which parts of the body passed during ecdysis. The requirement to moult highly spiniferous, dentate or pectinate appendages, broad swimming legs, a broad preabdomen and postabdominal epimera may have limited eurypterid disparity. The fossil record of certain eurypterid clades is confined largely to a few Lagerstätten. Some of the best-known eurypterid occurrences (i.e., in New York and Ontario) represent conditions favourable for ecdysis and the preservation of non-mineralized cuticle rather than settings normally inhabited by the arthropods, although the eurypterid locality at Kokomo, Indiana appears to represent a mass mortality. The reduction in suitable ecdysial refugia close to the end of the Silurian may have contributed to the decline and extinction of some eurypterid genera.