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Actinopterygian node M: Presence of premaxilla and antorbital, nearly vertical hyomandibular.
Pholidopleuriforms, such as Pholidopleurus - above - from the Mid Triassic of Switzerland have characteristically large and rectangular flank scales arranged in vertical rows along the entire length of their bodies. Additionally, the overall body plans of these basal actinopterygians were typically slender and elongated.
The pholidopleuriforms, as the peltopleuriforms and perleidiforms with which they were contemporaneous, are inferred to stem from the lineage from which more advanced actinopterygians also evolved. This hypothesis is based on their sharing trends towards the neopterygian body plan: a shift in the organisation of the tail, becoming almost entirely ray-supported, while the muscular dorsal lobe - although still present - is greatly reduced in these fish. The structure of jaw bones also shows similarities with the more derived clades.