Fossils of an over 1-meter-long Permian ray-finned fish (Actinopterygii) from the western USA highlight multiple origins of large body size in stem-group actinopterygians

Ray-finned fishes (Actinopterygii) include one out of every two species of vertebrate on Earth and exhibit extraordinary diversity in body size, ranging at adult length from <8 mm to over 7 m. The actinopterygian fossil record provides a means to reconstruct the evolutionary history of body size in ray-finned fishes, beginning with the earliest records of the clade in the Paleozoic Era. A literal reading of the fossil record of ray-finned fishes would suggest that body length, as a proxy for body size, was low (<1 m) throughout much of the Paleozoic. However, the literature shows a subset of rare, understudied, and typically poorly preserved fossils of large-bodied ray-finned fishes from Paleozoic deposits in Europe and North America. Description of fragmentary actinopterygian remains (USNM 457213, FMNH P. 25772, IMNH 2596/51199) from the Phosphoria Formation of Idaho and the Minnekahta Limestone of South Dakota shows that >1 m long ray-finned fishes were present in the lower Permian Phosphoria Sea of North America. The anatomy of USNM 457213, FMNH P. 25772, and IMNH 2596/51199 is consistent with stem-group actinopterygians grouped within the paraphyletic ‘palaeoniscoid’ wastebasket taxon, but do not preserve enough features to assign more specifically than the actinopterygian total group. Although USNM 457213, FMNH P. 25772, and IMNH 2596/51199 are poorly preserved relative to other Paleozoic-aged ray-finned fishes, such fossils of large-bodied Paleozoic-aged ray-finned fishes are rare and critical to reconstruct the evolutionary history of body size in actinopterygians. Description of USNM 457213, FMNH P. 25772, and IMNH 2596/51199 in conjunction with the literature on other >1 m stem-group ray-finned fishes indicates that large body size is associated with radically different morphologies across stem-group actinopterygians, suggesting multiple origins of increased size in distinct feeding niches.