A new genus and species of Devonian tetrapod, Brittagnathus minutus gen. et sp. nov., is described from a single complete right lower jaw ramus recovered from the Acanthostega mass-death deposit in the upper part of the Britta Dal Formation (upper Famennian) of Stensiö Bjerg, Gauss Peninsula, East Greenland. Visualisation by propagation phase contrast synchrotron microtomography (PPC-SRμCT) allows a complete digital dissection of the specimen. With a total jaw ramus length of 44.8 mm, Brittagnathus is by far the smallest Devonian tetrapod described to date. It differs from all previously knownDevonian tetrapods in having only a fang pair without a tooth row on the anterior coronoid, and a large posterior process on the posterior coronoid. The presence of an incipient surangular crest and a concave prearticular margin to the adductor fossa together cause the fossa to face somewhat mesially, reminiscent of the condition in Carboniferous tetrapods. A phylogenetic analysis places Brittagnathus crownward to other Devonian tetrapods, adjacent to the Tournaisian genus Pederpes. Together with other recent discoveries, it suggests that diversification of ‘Carboniferous-grade’ tetrapods had already begun before the end of the Devonian and that the group was not greatly affected by the end-Devonian mass extinction.

Synchrotron microtomography data set of Devonian tetrapod jaw NHMD 116368, holotype and only specimen of Brittagnathus minutus. Part 2

The specimen, NHMD 116368, (field number MGUH f.n. 1373) was collected in July 1987 from the Acanthostega-yielding horizon on Stensiö Bjerg, Gauss Peninsula, East Greenland. It was initially prepared mechanically, which revealed the posterior end of the lateral surface and the lower margin and prearticular on the medial surface. In September 2016 the specimen was imaged using propagation phase contrast synchrotron microtomography (PPC-SRmCT) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The scan was part of Experiment ES-505 and was made courtesy of Valéria Vaskaninova to whom the beamtime had been awarded. The voxel size of the scan was 13.49 mm, made with single distance phase retrieval and a propagation distance of 5m. The reconstructed volume was converted into a stack of 16 bit TIFF images.

Because each of the 1708 images is a separate file, and Dryad imposes a 1000-file limit on data sets, the stack has been split in two: this is Part 2, containing the last 735 images. Part 1 is available at https://doi.org/10.5061/dryad.sqv9s4n0k