A Permian fish reveals widespread distribution of neopterygian-like jaw suspension

<p>The actinopterygian crown group (comprising all living ray-finned fishes) originated by the end of the Carboniferous. However, most late Paleozoic taxa are stem actinopterygians, and broadly resemble stratigraphically older taxa. The early Permian †<em>Brachydegma</em> <em>caelatum</em> is notable for its three-dimensional preservation and past phylogenetic interpretations as a nested member of the neopterygian crown. Here, we use computed microtomography to redescribe †<em>Brachydegma</em>, uncovering an unanticipated combination of primitive (e.g., aortic canal; immobile maxilla) and derived (e.g., differentiated occipital ossifications; posterior stem of parasphenoid; two accessory hyoidean ossifications; double jaw joint) endoskeletal features relative to most other Paleozoic actinopterygians. Some of these features were previously thought restricted to the neopterygian crown. The precise phylogenetic position of †<em>Brachydegma</em> is unclear, with placements either on the polypterid stem, or as an early-diverging stem neopterygian. However, our analyses decisively reject previous placements of †<em>Brachydegma</em> in the neopterygian crown. Critically, we demonstrate that key-endoskeletal components of the hyoid portion of the suspensorium of crown neopterygians appeared deeper in the tree than previously thought.</p>