A fish for Phoebe: a new actinopterygian from the Upper Carboniferous Coal Measures of Saddleworth, Greater Manchester, UK, and a revision of Kansasiella eatoni

The origin of crown Actinopterygii has been dated to near the Devonian-Carboniferous boundary, but poor phylogenetic signal occludes the origin of modern actinopterygian biodiversity. Scarcity of comparative endoskeletal anatomy from this period likely contributes to the uncertainty. For example, only a handful of neurocrania have been described from the Carboniferous period despite an abundance of fossil taxa. Here we present a new actinopterygian, Phoebeannaia mossae gen. et sp. nov., from the Bashkirian Coal Measures of Saddleworth, Greater Manchester, UK, represented by an exceptionally preserved neurocranium and associated dermal bones. Morphological similarities to the Virgilian Kansasiella eatoni prompted comparative study and construction of a new neurocranial character matrix. Subsequent systematic analysis enabled identification of a cluster of similar Late Palaeozoic neurocrania, exploration of trends in braincase evolution across time, and investigation of potential causes of cladistic instability. Our neurocranial dataset reliably places this new specimen on the neopterygian stem near Kansasiella, but it struggles to incorporate extant taxa such as Polypteriformes, leading to uncertainty in branching pattern and inferred neurocranial transformation series. This work triples the number of complete Carboniferous neurocrania described with modern microcomputed tomography and provides a framework for future testing of large-scale hypotheses regarding the diversification and origin of ray-finned fishes.