A MIDDLE PERMIAN (ROADIAN) RAY-FINNED FISH (ACTINOPTERYGII) FROM THE MINNEKAHTA LIMESTONE OF SOUTH DAKOTA, USA

A low-quality fossil record and understudy of Late Paleozoic (Permo-Carboniferous) ray-finned fishes (Actinopterygii) obscures the interrelationships and phylogenetic position of extinct Paleozoic and Early Mesozoic actinopterygians. To help address this issue, we describe a ray-finned fish from the early Middle Permian (Roadian) Minnekahta Limestone of South Dakota. This taxon is represented by two specimens, including Field Museum of Natural History PF 3721, a partial three-dimensional head and trunk preserving the external anatomy of and some internal elements from the skull, paired fins, and scale cover. This fish has features of the wastebasket "paleoniscoid" group, including an immobile maxilla with a narrow suborbital process and a broad postorbital expansion, a heterocercal caudal fin, and rhombic ganoid scales. We conducted an equally weighted maximum parsimony analysis in PAUP with 73 other taxa and 222 characters that placed this taxon in a polytomy with other Late Paleozoic and Early Mesozoic "paleoniscoids" in the strict consensus tree. Although this fish bears superficial resemblance to the Triassic actinopterygian Pteronisculus, it differs from Pteronisculus in its scale morphology and in that its lacrimals do not contribute to the oral margin. Our description of this taxon provides new information on the sparse Middle Permian marine fossil record of ray-finned fishes. Also, our incorporation of this fish into a phylogenetic analysis helps to address the historical paucity of Permian taxa in studies of actinopterygian interrelationships.