A New Lower Permian Ray-Finned Fish (Actinopterygii) From South Dakota and the Use of Tree Space to Find Rogue Taxa in Phylogenetic Analysis of Morphological Data

The ray-finned fishes (Actinopterygii) include one out of two species of vertebrate on Earth today. The mineralized skeletons of ray-finned fishes are a common component of the vertebrate fossil record extending back 380 million years, providing a window into the history of actinopterygian diversification. The divergence of extant lineages from the “palaeoniscoids”, a grade of Paleozoic and early Mesozoic Era species, remains unresolved in analyses of morphological data despite more than four decades of phylogenetic research. We describe a new ray-finned fish, Tenupiscis dakotaensis gen et. sp. nov., from the Lower Permian (Kungurian) of South Dakota to strengthen our phylogenetic knowledge of Mississippian–Triassic actinopterygians. Our initial parsimony and Bayesian phylogenetic analyses were unable to resolve the relationships of Mississippian–Triassic “palaeoniscoids”. We analyzed the topological variation among the trees sampled in each phylogenetic search (tree space) to determine if uncertainty was concentrated in a small subset of species with highly uncertain phylogenetic relationships relative to other terminal taxa (rogue taxa) or distributed evenly amongst early actinopterygians. The relationships of fourteen species were unresolved in the parsimony strict consensus due to a single rogue taxon (“Kalops monophyrum”). Parsimony and Bayesian analyses with the rogue pruned or recoded find the initially unresolved Mississippian–Triassic “palaeoniscoids” (including Tenupiscis) branching from the actinopterygian stem or from the base of pan-Neopterygii. Our work supports the emerging consensus that Paleozoic Era ray-finned fishes include clades of stem actinopterygians and the earliest members of the actinopterygian crown group. We also demonstrate an approach to identifying and mitigating rogue taxon effects in phylogenetic analysis of morphological data from new fossil taxa.