New stem-lepidosaurs from Vellberg, Germany: Implications for palaeoecology in the early diversification of Lepidosauromorpha

Lepidosauromorphs account for roughly a third of the living diversity of land vertebrates and yet their origin and early evolutionary history remain highly contentious. The fossil record of early lepidosauromorphs has been historically very poor, but this has been changing in recent years with new taxa reported from Europe and the North America, in particular the contributions from Vellberg, South-Western Germany. Here, we describe four new early lepidosauromorph taxa from the same locality (Airistagiz seegesi, Hohlachia multidens, Klainjosaura staroskalja, gen. et sp. novae, and an unnamed taxon), raising the number of known lepidosauromorphs from three to seven. The new taxa share many similarities, but are at the same time very distinctive from the previous known ones. The importance of the Central European Basin for the origin of several reptile groups like archosauromorphs and turtles had already been demonstrated with iconic fossils like Protorosaurus and Pappochelys, but these new findings now include lepidosauromorphs, the second-most diverse group of amniotes, and highlights the importance of the systematic exploration of small taxa in Lagerstätten.

Methods
CT scanning

All specimens were CT-scanned at the Carl Zeiss Quality Excellence Center Stuttgart, with a Metrotom 800 Generation 1 scanner (S. Tomaschko Zeiss Computertomographie Dienstleistung, Essingen, Germany), except for SMNS 91319, which was CT scanned at the Carl Zeiss Quality Excellence Center Aalen, and SMNS 91110-B, CT scanned at the Senckenberg HEP, University of Tübingen with a Phoenix V|tome|x s240 (GE Sensing and Inspection Technologies GmbH, Wunstorf, Germany). The particular settings for each specimen can be found in the manuscript. Segmentations and measurements were made using the software VG Studio Max 2.0 and VG Studio Max 3.3 (Volume Graphics, Heidelberg, Germany).

Phylogenetic Analyses

Two different methods of phylogenetic analysis were used to assess the placement of the new taxa, a Parsimony and a Bayesian approach. The dataset used to assess the phylogenetic relationships of the new taxa was that of Ford et al. (2021) because it represents one of the latest additions to the lepidosauromorph fossil and anatomical record which also included all pertinent Vellberg taxa. Given the close anatomical similarity of the new taxa and the high incompleteness two of them, only the remaining two were scored in the matrices. In addition to the exclusion of Palaeagama, as carried out in the original study, modifications to character scorings were made following recent publications on key taxa, namely: Prolacerta broomi (Sobral 2023), Protorosaurus speneri (Schoch et al. in review), and Youngina capensis (Hunt et al. 2023). Furthermore, some scorings for Vellbergia barthomolaei (Sobral et al. 2020) were also modified. A complete list of modifications can be found in the Supplemental Material.

The parsimony analyses were performed in the software TNT (Goloboff & Morales 2003) with an equal weight approach. A TBR search with 1,000 replications each and 10 trees stored per replication was applied. The Bayesian analyses were run in MrBayes 3.2.6 (Ronquist et al. 2012) on the CIPRES Science Gateway server (phylo.org) with the same settings as applied by the original study of Ford et al. (2021). The character–taxon matrix used in the analyses, as well as the TNT and MrBayes scripts, can also be found in the Supplemental Material.