Horseshoe crabs are extant chelicerates with a fossil record extending back to the Ordovician. Despite the documentation of their long evolutionary history, xiphosurids are rarely preserved within fossil assemblages due to their unmineralized cuticular exoskeleton. However, in exceptional circumstances, an abundance of fossil xiphosurid specimens have been documented. The Moscovian-aged Mazon Creek Konservat-Lagerstätte represents one such fossil deposit with a high abundance and diversity of xiphosurids. Although fairly well known, the Paleolimulus specimens from the Mazon Creek have not yet been subject to a thorough taxonomic examination. In the light of recent efforts to organise Paleolimulus, we revisit this undescribed material, erect Paleolimulus mazonensis n. sp., and present a phylogenetic analysis that places P. mazonensis n. sp. as a sister taxon to P. signata (Beecher, 1904). The palaeoecology and possible ontogeny of P. mazonensis n. sp. are presented, as well as a statement on the future directions for understanding this xiphosurid genus.
Xiphosurida, horseshoe crabs, exceptional preservation, Paleozoic, Carboniferous, Paleolimulidae, new species