Abstract Praearcturus gigas Woodward is a large arthropod of disputed affinity from the fluvial St Maughans Formation (Lower Devonian, Lochkovian) of the Old Red Sandstone of England and Wales. Originally described as an isopod in the nineteenth century, and subsequently compared to various arthropod groups, it was re‐described with limited illustration as a gigantic scorpion in the 1980s. Recently, this interpretation has been challenged, warranting a modern revision of the material. Illustrating P. gigas with camera lucida drawings, light photography and tomographic data, we present a re‐description of the type material and assign several other specimens from the same formation to this taxon, thence identifying Brontoscorpio anglicus Kjellesvig‐Waering and Bennettarthra annwnensis Fayers et al. as junior synonyms of P. gigas . Several characters supporting a scorpion affinity are present in P. gigas , including large pedipalps with a fixed and movable finger, a stridulatory surface on one of the coxae, and an elongate subtriangular sternum morphology shared with the unambiguous Silurian scorpion Eramoscorpius brucensis Waddington et al. (Wenlock, Canada). Uniquely among scorpions, P. gigas has lateral epimera on the mesosomal tergites, and combined with the fluvial environment in which the fossils are preserved, we suggest that P. gigas may have been aquatic or amphibious. Finally, we review the evidence for scorpion gigantism and discuss the evolutionary context of a large arachnid predator in the Early Devonian.
Howard et al. (Fri,) studied this question.