DOI: 10.5061/dryad.4xgxd25jv
title: Data for: A new ‘acanthothoracid’ placoderm from the Arctic Canada (Early Devonian) and its bearing on the evolution of jaws and teeth

description: The origin of jaws and teeth represents one of the most formative episodes
 in our own evolutionary history. However, this event is poorly understood
 for a lack of detailed knowledge of key lineages, including the
 ‘acanthothoracid’ placoderms, which were among the earliest jawed
 vertebrates. Here we describe Romundina gagnieri sp. nov., a new species
 of ‘acanthothoracid’ from the Early Devonian of Arctic Canada based on
 computed and synchrotron tomographies. The new species displays anterior
 supragnathal plates with teeth that we have characterised using
 synchrotron tomography. Our study shows that teeth are arranged in a
 concentric manner and that the pattern of tooth addition is centrifugal,
 including an anterior addition. Overgrowing odontodes, present on the
 anterior part of the gnathal plates, are covering teeth that can display a
 hypermineralised layer (likely reflecting the earliest stage of teeth
 during the ontogeny) or be partially broken. These overgrowing odontodes
 develop in successive steps and without obvious organization. The presence
 of a pair of anterior supragnathal plates on the ethmoid part of the
 endocranium, as well as the growth process of these plates in R. gagnieri
 sp. nov. are similar to the conditions seen notably in arthrodires arguing
 for those as the gnathostome ancestral condition.
description: # Data for: A new ‘acanthothoracid’ placoderm from the Arctic Canada
 (Early Devonian) and its bearing on the evolution of jaws and teeth
 [https://doi.org/10.5061/dryad.4xgxd25jv](https://doi.org/10.5061/dryad.4xgxd25jv) We have submitted the raw X-ray projection data of the incomplete skull (in two parts, specimen MNHN.F.CPW30) of *Romundina gagnieri* sp. nov. **(CPW30_fragment_tomo-B_50_kV_recon_tiff_ushor_16_bit.zip** and **CPW30_tomo-A_recon.zip**). Data used for the anatomical description of the endocranium. We have also submitted the Synchrotron raw slice data of five regions of interest on the prenatal region (specimen MNHN.F.CPW9) of *Romundina gagnieri* sp. nov. (**ROI1_-_MR289f.zip**, **ROI2_-_MR287e.zip** **ROI3_-_MR289g.zip, ROI4_-_MR287f.zip** and **ROI5_-_MR290b.zip**). Data used for the description of teeth (internal) and dermal (external) odontodes. ## Description of the data and file structure The data include: * 2 files of CT-scan raw data corresponding to the 3D model in Figures 3 and 5. MNHN.F.CPW30 was scanned using a Zeiss Xradia 520 Versa micro-CT scanner, 50 kV (Naturalis Biodiversity Center, Leiden). MNHN.F.CPW30 is preserved in two parts. CPW30a corresponds to an almost complete endocranium, whereas CPW30b represents only a fragment of it (of the left part). MNHN.F.CPW30a and b were scanned independently, with the voxel dimensions of 0.023 mm and 0.012 mm for CPW30a (number of slices of 1018) and CPW30b (number of slices of 1015), respectively. Both datasets were merged virtually and segmented using AVIZO 2019.3 ([www.fei.com](http://www.fei.com)). * 5 files of Synchrotron raw data corresponding to the 5 Regions of Interest (ROI) in Figure 2. Data were obtained thanks to the Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) at the TOMCAT (X02DA) beamline of the Swiss Light Source, Paul Scherrer Institute, Switzerland. ROI 1 corresponds to the medial area on the right gnathal plate. ROI 2 corresponds to the lateral area on the left gnathal plate. ROI 3 corresponds to the connection area between the right gnathal plate and the ventral expansion of the premedian plate. ROI 4 corresponds to an area on the ventral expansion of the premedian plate. ROI 5 corresponds to an area on the dorsal portion of the premedian plate. These regions of interest were scanned with 1501 (ROIs 2 and 4) or 1001 (ROIs 1, 3, and 5) projections distributed equi-angularly over 180º, using a 10x objective, resulting in a dataset with voxel dimensions of 0.65 µm. The measurement energy was 35 (ROIs 1, 3, and 5) or 32 (ROIs 2 and 4) keV with an exposure time of 1800 (ROIs 1, 3, and 5) or 2000 (ROIs 2 and 3) milliseconds. Phase retrieval was used, applying a Paganin algorithm (Paganin *et al.*, 2002) to the corrected projections, and consequently, tomograms were reconstructed for all ROIs. These data were analysed using AVIZO 2019.3 ([www.fei.com](http://www.fei.com)). Volume rendering of odontodes was made, slice by slice, from the tip to the base.