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

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 †Brachydegma caelatum 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 †Brachydegma, 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 †Brachydegma is
unclear, with placements either on the polypterid stem, or as an
early-diverging stem neopterygian. However, our analyses decisively reject
previous placements of †Brachydegma 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.