A new sphenodontian (Diapsida: Lepidosauria) from the Upper Triassic of Germany and its implications for the mode of sphenodontian evolution

The Arnstadt Formation of Saxony-Anhalt, Germany has yielded some of Germany’s most substantial finds of Late Triassic tetrapods, including the sauropodomorph Plateosaurus and the stem-turtle Proganochelys. Here, we describe an almost complete skull of a new sphenodontian taxon from this formation (Norian, 227-208 Ma), making it the oldest known articulated sphenodontian skull from Europe and one of the oldest in the world. The material is represented by the dermal skull roof and by the complete maxilla and temporal region, as well as parts of the palate, braincase, and lower jaw. A phylogenetic assessment recovers it as a basal sphenodontian closely related to Planocephalosaurus and to Eusphenodontia, making it the earliest-diverging sphenodontian known with an articulated skull. Its cranial anatomy is generally similar to the well-known Diphydontosaurus avonis from the Rhaetian of England, showing that this successful phenotype was already established in the clade around 10 myr earlie..., (a)   Computed Tomography
The holotype MB.R.4520.2 is housed in the fossil reptile collection of the Museum für Naturkunde in Berlin (Germany). µCT scans were performed in house using a Phoenix|x-ray Nanotom S tomography machine (GE Sensing and Inspection Technologies GmbH, Wunstorf, Germany) with a voltage of 110 kV and a current of 150 µA, capturing 2,000 images with an exposure time of 750 ms and a resolution of 10.23 µm. Slices were reconstructed using the datos|x v.2.3.0.844 - RTM reconstruction software (GE Sensing and Inspection Technologies GmbH, Phoenix—x-ray) and the resulting volume was manually segmented and analysed in VG Studio Max 3.3 (Volume Graphics GmbH, Heidelberg, Germany) at the 3D-Visualisation Laboratory at the Museum of Natural History Berlin using the region grower and pen tools.
(b)   Time-calibrated phylogenetic analysis
A sphenodontian phylogeny was constructed to explore the relationship of Parvosaurus harudensis within Rhynchocephalia using the morphologica..., , # A new sphenodontian (Diapsida: Lepidosauria) from the Upper Triassic of Germany and its implications for the mode of sphenodontian evolution

[https://doi.org/10.5061/dryad.280gb5mwd](https://doi.org/10.5061/dryad.280gb5mwd)

## Description of the data and file structure

Supplementary material includes:

1\) Bayesian phylogenetic analysis;
2\) Maximum Parsimony phylogenetic analysis;
3\) R script for the evolutionary rates analysis;
4\) input and output data and calculations made for the phylogenetic and rates analyses;
5\) a PDF file containing additional figures showing anatomical features, phylogenetic results and evolutionary rates results;
6\) the original μCT dataset;
7\) the reconstructed 3D surface models.