Data for: A new ‘acanthothoracid’ placoderm from the Arctic Canada (Early Devonian) and its bearing on the evolution of jaws and teeth

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 ..., , , # 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 3...,