Morphological variation in the Pennsylvanian horseshoe crab Euproops danae (Meek & Worthen, 1865) (Xiphosurida, Euproopidae) from the lower Mercer Shale, Windber, Pennsylvania, USA

Abstract

Examination of 36 specimens of the Pennsylvanian horseshoe crab Euproops danae (Meek & Worthen, 1865) from a previously unreported occurrence in the lower Mercer Shale exposed in an abandoned strip mine south from Windber, Pennsylvania, USA, document ontogenetic changes in prosomal morphology. Intercardiophthalmic transverse bars become less pronounced as ophthalmic spines become longer in larger, older specimens through approximately seven instar stages. It remains unclear if the presence or absence of ophthalmic spines is taphonomic, regardless of developmental stage. The holotype of E. danae is illustrated photographically for the first time.