Acanthorhachis, a new genus of shark from the Carboniferous (Westphalian) of Yorkshire, England

Abstract

AbstractAn association of diverse hollow spines and dermal denticles (ichthyoliths) from the Carboniferous (Westphalian) of Todmorden, Yorkshire, England are attributed to a new genus of enigmatic shark that may lie close toListracanthusNewberry & Worthen, 1870. Scanning electron microscopy shows that denticle morphology is highly variable, but forms a morphocline including elongate multi-spined elements as well as robust dome-like stellate denticles and recurved spinose elements. Histological analysis suggests an absence of enameloid. Continuous variation of form between elongate multi-cusped spines to boss-like circular denticles shows that all previously described Palaeozoic species ofListracanthusare probably junior synonyms of the type speciesL.hystrixNewberry & Worthen, 1870. The status ofListracanthusas a surviving ‘Lilliputian’ taxon after the Permian extinction is questioned. Although the new specimen has affinities withListracanthus, significant differences in the form of the posterior spines on elongate denticles warrants its placement in the new genusAcanthorhachisgen. nov. The family Listracanthidae is erected to accommodateListracanthusandAcanthorhachis.