The Palaeozoic record of chondrichthyans (sharks, rays, chimaeras, extinct relatives) and thus our knowledge of their anatomy and functional morphology is poor because of their predominantly cartilaginous skeletons. Here, we report a previously undescribed symmoriiform shark, Ferromirum oukherbouchi, from the Late Devonian of the Anti-Atlas. Computed tomography scanning reveals the undeformed shape of the jaws and hyoid arch, which are of a kind often used to represent primitive conditions for jawed vertebrates. Of critical importance, these closely fitting cartilages preclude the repeatedly hypothesized presence of a complete gill between mandibular and hyoid arches. We show that the jaw articulation is specialized and drives mandibular rotation outward when the mouth opens, and inward upon closure. The resultant eversion and inversion of the lower dentition presents a greater number of teeth to prey through the bite-cycle. This suggests an increased functional and ecomorphological disparity among chondrichthyans preceding and surviving the end-Devonian extinctions.

软骨鱼类（鲨鱼，射线，chi虫，已灭绝的亲属）的古生代记录，因此我们对它们的解剖学和功能形态的了解很差，因为它们主要是软骨骨架。在这里，我们报告一个以前未描述的sym鲨，Ferromirum oukherbouchi，来自反地图集的晚泥盆纪。计算机断层扫描可以显示颌骨和舌骨弓的未变形形状，它们经常被用来表示颌骨脊椎动物的原始状况。至关重要的是，这些紧密贴合的软骨排除了在下颌和舌骨弓之间反复假想完整complete的可能性。我们表明，颌关节是专门的，当嘴张开时会驱动下颌向外旋转，闭合时会向内驱动。牙列的外翻和内翻导致更多的牙齿在咬合循环中被捕食。这表明在德文氏族灭绝之前和幸存的软骨鱼类之间功能和生态形态差异增加。