A taxonomic revision of orthosternous scorpions from the English Coal-measures aided by X-ray Micro-Tomography (XMT)

Abstract

Fossil scorpion systematics – particularly that of the diverse assemblage found in Carboniferous Coal Measure deposits – are problematic, being characterised by a large number of frequently monotypic taxa, based on a limited set of characters. These Palaeozoic scorpions have the potential to elucidate the nature of the scorpion stemgroup and hence to inform long running debates regarding the origin of the crown group and relationships between extant lineages. Carboniferous taxa are often found in siderite concretions and can be preserved in three dimensions. This study investigates two such fossils of the species Compsoscorpius buthiformis (Pocock, 1911) with the aid of X-ray Micro-Tomography (XMT) and computer reconstruction. These scans reveal important new details of the anatomy, such as the walking legs, that allow more detailed comparison with coeval taxa. Many of these taxa are revealed here to be junior synonyms of C. buthiformis and previous taxonomic practice, as it relates to Coal Measures scorpions, is criticised. The ecology of C. buthiformis is also reviewed in light of the new evidence from XMT. In particular, aspects of its walking leg and metastomal anatomy are analogous to that of extant lithophilic and ‘errant’ leaf-litter scorpions.