Patesia n. gen., a new Late Devonian stem xiphosurid genus

Abstract

Xiphosura, the so-called horseshoe crabs, are a group of extant marine chelicerates that have a fossil record extending back to the Lower Ordovician. Their temporal range, coupled with a supposed record of bradytelic evolution has made them a focus of palaeontological consideration for over two centuries. As such, there are an array of taxa erected during the 20^th century that have remained unexamined in light of new material and revised phylogenetic theories. Stem xiphosurids in particular require further research to uncover the diversity and disparity of non-crown group horseshoe crabs. To align with the recent increase in mid to late Paleozoic horseshoe crab research, we reconsider the stem xiphosurids <i>"Kasibelinurus" randalli</i> and <i>"Bellinurus" alleganyensis</i> from the Late Devonian of Pennsylvania and New York State. We conclude that they are synonyms and belong in neither <i>Kasibelinurus</i> nor <i>Bellinurus</i>, and the new genus, <i>Patesia</i>, is erected to accommodate them. Reconsidering stem xiphosurids highlights that particularly in the Late Devonian there was a high disparity of form. One such stem xiphosurid may represent the morphological stock that gave rise to the Carboniferous taxa and the first xiphosurid radiation.