Data from: An early chondrichthyan and the evolutionary assembly of a shark body plan

Although relationships among the major groups of living gnathostomes are well established, the relatedness of early jawed vertebrates to modern clades is intensely debated. Here, we provide a new description of Gladbachus, a Middle Devonian (Givetian ~385-million-year-old) stem chondrichthyan from Germany, and one of the very few early chondrichthyans in which substantial portions of the endoskeleton are preserved. Tomographic and histological techniques reveal new details of the gill skeleton, hyoid arch and jaws, neurocranium, cartilage, scales and teeth. Despite many features resembling placoderm or osteichthyan conditions, phylogenetic analysis confirms Gladbachus as a stem chondrichthyan and corroborates hypotheses that all acanthodians are stem chondrichthyans. The unfamiliar character combination displayed by Gladbachus, alongside conditions observed in acanthodians, implies that pre-Devonian stem-chondrichthyans are severely under-sampled and strongly supports indications from isolated scales that the gnathostome crown group originated at the latest by the early Silurian (~440 mya). Moreover, phylogenetic results highlight the likely convergent evolution of conventional chondrichthyan conditions among earliest members of this primary gnathostome division, while skeletal morphology points towards the likely suspension feeding habits of Gladbachus, suggesting a functional origin of the gill slit condition characteristic of the vast majority of living and fossil chondrichthyans.尽管现生有颌脊椎动物（gnathostomes）的主要类群间的系统发育关系已得到明确阐释，但早期有颌脊椎动物与现生演化支的亲缘关系仍存在激烈争议。本研究对产自德国的中泥盆世（吉维特期，约3.85亿年前）干群软骨鱼类（stem chondrichthyan）格拉巴鱼（Gladbachus）进行了全新形态描述，该物种是少数保存有大量内骨骼的早期软骨鱼类之一。通过断层扫描与组织学技术，本研究揭示了其鳃骨骼、舌弓与颌骨、脑颅、软骨、鳞片以及牙齿的全新细节。尽管其诸多特征与盾皮鱼类或硬骨鱼类的性状相似，但系统发育分析证实格拉巴鱼属于干群软骨鱼类，并支持了所有棘鱼形类均为干群软骨鱼类的假说。格拉巴鱼所展现出的独特性状组合，结合棘鱼形类所呈现的相关性状，表明泥盆纪前的干群软骨鱼类采样严重不足；同时该结果也有力支持了来自孤立鳞片的证据，即有颌类冠群最晚至早志留世（约4.4亿年前）就已起源。此外，系统发育分析结果显示，该主要有颌类支系的早期成员中，典型软骨鱼类的性状很可能经历了趋同演化；而骨骼形态学特征则表明格拉巴鱼大概率为滤食性动物，这为绝大多数现生与化石软骨鱼类所特有的鳃裂性状的功能起源提供了重要依据。