Reassessment of ‘Cladodus’neilsoniTraquair: a primitive shark from the Lower Carboniferous of East Kilbridge, Scotland

The partly articulated specimen of the Palaeozoic (Early Carboniferous) chondrichthyan ‘Cladodus’neilsoni Traquair from East Kilbride has been known since the late nineteenth century. As such, ‘C.’neilsoni Traquair has been cited in numerous publications, but it has become increasingly clear that its anatomy and systematic affinities are obscure. This comprehensive redescription of ‘C.’neilsoni reveals new details of the neurocranium (including presence of an otico-occipital fissure), dentition, visceral arches (clarifying the condition of the basibranchial pattern plus elongate copula), and pectoral fin. These data refute previously suggested synonymies, such as between ‘C’neilsoni and the contemporaneous Bearsden Stethacanthus. Attribution of ‘C.’neilsoni to the taxonomically unsupportable genus ‘Cladodus’ is rejected, and the species is redesignated as Gutturensisneilsoni gen. nov. Preliminary cladistic analysis places Gutturensisneilsoni within a polytomy including Stethacanthus, the symmoriid Cobelodus, and the root of a monophyletic group of neoselachian-like genera. ‘ Cladodont’ as a diagnostic term for early chondrichthyan teeth is found to be insufficiently precise, referring to an ill-defined grade of tooth morphologies present in a wide variety of Palaeozoic genera.