Data from: Evolutionary origins of teeth in jawed vertebrates: conflicting data from acanthothoracid dental plates (‘Placodermi’)

Placoderms (Devonian fossil fishes) are resolved phylogenetically to the base of jawed vertebrates and provide important evidence for evolutionary origins of teeth, particularly with respect to the Arthrodira. The arthrodires represent a derived group of placoderms; the dentition of other more primitive placoderms such as the acanthothoracids is less well known. Articulated acanthothoracid dental plates are rare; x-ray computed tomography of a single, unique specimen, along with 3D segmentation of bone, oral denticles and vascular spaces, provides intrinsic developmental and topological information relevant to tooth origins. Recently, a disarticulated element was identified as a dental plate of the acanthothoracid Romundina stellina, with synchrotron microtomography providing characters to comment on ongoing debates regarding the evolution of teeth. We used segmental quantitative methods to re-analyse this data, for comparison to the articulated and unquestionable acanthothoracid dental plates above. We demonstrate substantial differences between these, disputing the identity of the isolated plate of R. stellina as a dental plate, and thus its relevance to questions of tooth evolution.

盾皮鱼（Placoderms，泥盆纪化石鱼类）经系统发育分析被定位于有颌脊椎动物的基部类群，为牙齿的演化起源提供了重要证据，尤其在节甲鱼类（Arthrodira）的相关研究中意义显著。节甲类属于衍化程度较高的盾皮鱼类类群；而棘胸鱼类（acanthothoracids）等更为原始的盾皮鱼类的齿系研究则相对匮乏。关联保存的棘胸鱼类齿板标本极为罕见，此前针对一件独特的单份标本开展的X射线计算机断层扫描（X-ray computed tomography），结合骨骼、口腔齿突与血管腔的三维分割工作，获取了与牙齿起源相关的内在发育与拓扑学信息。近期，一件分离的化石元素被认定为棘胸鱼类Romundina stellina的齿板，同步辐射显微断层扫描（synchrotron microtomography）所得的性状数据为当前围绕牙齿演化的诸多争议提供了讨论依据。本研究采用分段定量方法对该数据集进行重新分析，以与前文所述关联保存且确凿无疑的棘胸鱼类齿板进行对比。研究结果显示二者存在显著差异，据此质疑该分离的R. stellina标本为齿板的身份，进而否定了其在牙齿演化相关研究中的学术相关性。