A new, exceptionally well-preserved Permian actinopterygian fish from the Minnekahta Limestone of South Dakota, USA

The evolutionary history of Palaeozoic and early Mesozoic ray-finned fishes (Actinopterygii) is obscured by an incomplete fossil record and under-study of late Palaeozoic (Permo-Carboniferous) actinopterygians. To help address this issue, we describe a new species of ray-finned fish, Concentrilepis minnekahtaensis gen. et sp. nov., from the late early Permian (Kungurian) Minnekahta Limestone of South Dakota (USA). This taxon is represented by Field Museum of Natural History FMNH PF 3721, an exceptionally well-preserved partial three-dimensional head and trunk preserving the external anatomy and some internal elements from the skull, paired fins and scale cover. Concentrilepis is also represented by Yale Peabody Museum 18649, a laterally compressed individual that preserves the posterior portion of the body. This taxon has features of the paraphyletic ‘paleoniscoids’, including an immobile maxilla with a narrow suborbital process and a broad postorbital expansion, a heterocercal caudal fin, and rhombic ganoid scales. Concentrilepis is distinguished from similar species by the dual lateral expansions on its frontal (= parietal of sarcopterygians), the exclusion of the lacrimal from the oral margin, and lateral scales that are longer than deep and ornamented with straight, concentric ridges at their margins and diagonal ridges at their centres. We conducted a maximum parsimony analysis in PAUP and a Bayesian analysis with the Mkv model in MrBayes with 73 other taxa and 222 characters that placed this taxon in a polytomy with other late Palaeozoic and early Mesozoic ‘paleoniscoids’. We also found that the application of Bayesian and parsimony techniques in tandem provided the necessary caution in interpreting our results and focused direction for future study. Continued efforts to gather more morphological data from ‘paleoniscoids’ in concert with the development and testing of novel phylogenetic characters and inference techniques will be necessary to improve our understanding of the interrelationships of late Palaeozoic and early Mesozoic actinopterygians. http://zoobank.org/urn:lsid:zoobank.org:pub:9F12F99D-A33A-41C2-AC34-F4936786020B

古生代（Palaeozoic）与早中生代（early Mesozoic）辐鳍鱼（Actinopterygii）的演化历史，因化石记录残缺不全且晚古生代（二叠-石炭纪，Permo-Carboniferous）辐鳍鱼类研究不足而长期模糊不清。为解决这一问题，我们记述了来自美国南达科他州早二叠世晚期（孔谷阶，Kungurian）明尼卡塔灰岩（Minnekahta Limestone）的辐鳍鱼类新属新种：Concentrilepis minnekahtaensis gen. et sp. nov.。该类群以两件标本为代表：其一为菲尔德自然历史博物馆馆藏FMNH PF 3721号标本，是一件保存异常完好的部分三维头部与躯干化石，保留了外部解剖结构以及头骨、成对鳍与鳞片覆盖层的部分内部结构；其二为耶鲁大学皮博迪自然历史博物馆馆藏18649号标本，该标本为侧扁个体，保留了身体后部区域。该类群具备并系群“古鳕类（paleoniscoids）”的特征，包括具有狭窄眶下突与宽阔眶后扩展区的不可动上颌骨、歪形尾鳍，以及菱形硬鳞。同心鳞鱼属（Concentrilepis）可通过以下特征与近似物种区分：其一，额骨（=肉鳍鱼类的顶骨）具有双侧扩展结构；其二，泪骨不参与口缘构成；其三，侧鳞长大于高，鳞片边缘饰有平直的同心脊纹，中央区域带有斜向脊纹。我们使用PAUP软件开展最大简约法分析，并在MrBayes软件中采用Mkv模型进行贝叶斯分析，分析纳入73个其他分类单元与222个形态特征，结果显示该类群与其他晚古生代及早中生代“古鳕类”共同构成一多歧支。我们同时发现，联合应用贝叶斯与最大简约法分析技术，可为研究结果的解读提供必要的严谨性，并为未来研究指明方向。未来仍需持续收集“古鳕类”的形态学数据，同时开发并验证新型系统发育特征与推断技术，以增进我们对晚古生代及早中生代辐鳍鱼类演化关系的认知。http://zoobank.org/urn:lsid:zoobank.org:pub:9F12F99D-A33A-41C2-AC34-F4936786020B