Igielman Ben, Figueroa Rodrigo Tinoco, Higgins Robert R, Pierce Stephanie E, Coates Michael I, Troyer Emily M, Fernandez Vincent, Dollman Kathleen, Lu Jing, Zhu Min, Friedman Matt, Giles Sam
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.
Museum of Paleontology, University of Michigan, Ann Arbor, Michigan, USA.
Anat Rec (Hoboken). 2025 Jul 21. doi: 10.1002/ar.70005.
Actinopterygii is a major extant vertebrate group, but limited data are available for its earliest members. Here we investigate the morphology of Devonian actinopterygians, focusing on the lower jaw. We use X-ray computed tomography (XCT) to provide comprehensive descriptions of the mandibles of 19 species, which span the whole of the Devonian and represent roughly two-thirds of all taxa known from more than isolated or fragmentary material. Our findings corroborate previous reports in part but reveal considerable new anatomical data and represent the first detailed description for roughly half of these taxa. The mandibles display substantial variation in size, spanning more than an order of magnitude. Although most conform to a generalized pattern of a large dentary and one or two smaller infradentaries, XCT data reveal significant differences in the structure of the jaw and arrangement of teeth that may be of functional relevance. We report the presence of a rudimentary coronoid process in several taxa, contributed to by the dentary and/or infradentaries, as well a raised articular region, resulting in a mandible with an offset bite and that functions as a bent level arm. Among the most striking variation is that of tooth morphology: several taxa have heterodont dentary teeth that vary in size and orientation, and multiple variations on enlarged, whorl-like and posteriorly-oriented anterior coronoid dentition are observed. We use these new data to revise morphological characters that may be of phylogenetic significance and consider the possible functional implicationds of these traits. The observed variation in mandible form and structure suggests previously unappreciated functional diversity among otherwise morphologically homogenous Devonian ray-finned fishes.
辐鳍鱼纲是现存的主要脊椎动物类群，但关于其最早成员的数据有限。在此，我们研究泥盆纪辐鳍鱼的形态，重点关注下颌。我们使用X射线计算机断层扫描（XCT）对19个物种的下颌进行全面描述，这些物种涵盖了整个泥盆纪，约占所有已知分类单元的三分之二，而这些分类单元不仅仅是孤立或零碎的材料。我们的研究结果部分证实了先前的报道，但也揭示了大量新的解剖学数据，并且是对大约一半分类单元的首次详细描述。下颌在大小上有很大差异，跨度超过一个数量级。尽管大多数下颌符合一个大齿骨和一两个较小的下齿骨的一般模式，但XCT数据揭示了颌骨结构和牙齿排列的显著差异，这些差异可能具有功能相关性。我们报告了在几个分类单元中存在由齿骨和/或下齿骨形成的雏形冠状突，以及一个凸起的关节区域，从而形成一个具有偏移咬合且起弯曲杠杆作用的下颌。最显著的变异之一是牙齿形态：几个分类单元的齿骨牙齿具有异型齿，大小和方向各不相同，并且观察到扩大的、螺旋状的和向后定向的前冠状突齿列有多种变异。我们利用这些新数据来修订可能具有系统发育意义的形态特征，并考虑这些特征可能的功能含义。观察到的下颌形态和结构的变异表明，在形态上原本相似的泥盆纪辐鳍鱼类中存在以前未被认识到的功能多样性。
