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The Carboniferous radiation of fishes was marked by the convergent appearance of then-novel but now common ecomorphologies resulting from changes in the relative proportions of traits, including elongation of the front of the skull (rostrum). The earliest ray-finned fishes (Actinopterygii) with elongate rostra are poorly known, obscuring the earliest appearances of a now widespread feature in actinopterygians. We redescribe Tanyrhinichthys mcallisteri, a long-rostrumed actinopterygian from the Upper Pennsylvanian (Missourian) of the Kinney Brick Quarry, New Mexico. Tanyrhinichthys has a lengthened rostrum bearing a sensory canal, ventrally inserted paired fins, posteriorly placed median fins unequal in size and shape, and a heterocercal caudal fin. Tanyrhinichthys shares these features with sturgeons, but lacks chondrostean synapomorphies, indicating convergence on a bottom-feeding lifestyle. Elongate rostra evolved independently in two lineages of bottom-dwelling, freshwater actinopterygians in the Late Pennsylvanian of Euramerica, as well as in at least one North American chondrichthyan (Bandringa rayi). The near-simultaneous appearance of novel ecomorphologies among multiple, distantly related lineages of actinopterygians and chondrichthyans was common during the Carboniferous radiation of fishes. This may reflect global shifts in marine and freshwater ecosystems and environments during the Carboniferous favouring such ecomorphologies, or it may have been contingent on the plasticity of early actinopterygians and chondrichthyans.

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