Styracopterid ( A ctinopterygii) ontogeny and the multiple origins of post‐ H angenberg deep‐bodied fishes

The C arboniferous fish family S tyracopteridae ( A ctinopterygii) originated as part of the initial radiation of ray‐finned fishes following the end‐ D evonian H angenberg extinction. Specimens of S tyracopterus fulcratus ( T raquair, 1890) have been collected from post‐extinction T ournaisian and V isean S cottish sediments for over 100 years, including sites containing some of the earliest ‘ R omer's G ap’ tetrapods . Re‐examination of this supposedly long‐lived, static species has revealed two genera, S tyracopterus and F ouldenia   W hite, 1927, divergent from each other and previous descriptions. Here, we show that styracopterids are among the earliest actinopterygians with durophagous dentition and toothplates, the latter likely to have derived from the ectopterygoids and coronoids. On the basis of this and other traits, such as the presence of an enameloid ‘beak’, the fusiform styracopterids are linked to some, but not all, the deep‐bodied actinopterygians previously placed in the suborder P latysomoidei. A new plesion, E urynotiformes, is erected to contain the styracopterids, the deeply fusiform E urynotus and the widespread A mphicentrum , among other laterally compressed fishes. This implies that platysomoids are polyphyletic: deep‐bodied and/or durophagous fishes evolved multiple times following the H angenberg event. Reconstructed styracopterid growth series show that trunk depth increased during maturation, mirroring the shape variation observed among the E urynotiformes. Other ontogenetic changes involve fin‐ray differentiation, jaw form, dermal bone ornamentation, and scale morphology; all of these are widely used as actinopterygian diagnostic characters. Further investigation of E urynotiformes should reveal the extent of evolutionary and ontogenetic change within the earliest actinopterygian radiation, and are likely to rewrite their phylogeny. © 2013 The Linnean Society of London