DOI: 10.5061/dryad.d2547d7zs
title: A tiny new Middle Triassic stem-lepidosauromorph from Germany: implications for the early evolution of lepidosauromorphs and the Vellberg fauna

description: The Middle Triassic was a time of major changes in tetrapod faunas
 worldwide, but the fossil record for this interval is largely obscure for
 terrestrial faunas. This poses a severe limitation to our understanding on
 the earliest stages of the diversification of lineages representing some
 of the most diverse faunas in the world today, such as lepidosauromorphs
 (e.g., lizards and tuataras). Here, we report a tiny new lepidosauromorph
 from the Middle Triassic from Vellberg (Germany), which combines a mosaic
 of features from both early evolving squamates and rhynchocephalians, such
 as the simultaneous occurrence of a splenial bone and partial development
 of acrodonty. Phylogenetic analyses applying different optimality
 criteria, and combined morphological and molecular data, consistently
 recover the new taxon as a stem-lepidosauromorph, implying
 stem-lepidosauromorph species coinhabited areas comprising today’s central
 Europe at the same time as the earliest known rhynchocephalians and
 squamates. It further demonstrates a more complex evolutionary scenario
 for dental evolution in early lepidosauromorphs, with independent
 acquisitions of acrodonty early in their evolutionary history. The small
 size of most terrestrial vertebrates from Vellberg is conspicuous,
 contrasting to younger Triassic deposits worldwide, but comparable to
 Early Triassic faunas, suggesting a potential long-lasting Lilliput effect
 this fauna.
description: <strong>Specimen availability</strong>. The holotype
 and only specimen of the new taxon is housed in the Staatliches Museum für
 Naturkunde Stuttgart, Germany under the number SMNS 91590. The anatomical
 analysis was made with the aid of computed-tomography (CT) scans performed
 with a Metrotom 800 Generation 1 scanner (S. Tomaschko Zeiss
 Computertomographie Dienstleistung, Essingen, Germany) using 110 kV and
 265 μA at 500 ms and a voxel size of 17,94 μm. Segmentations and
 measurements were made in the software VG Studio Max 2.0 (Volume Graphics,
 Heidelberg, Germany). A complete anatomical description is provided in the
 Supplementary Material. <br>
 <strong>Morphological and molecular data sets</strong>. In
 order to assess the phylogenetic placement of
 <em>Vellbergia bartholomaei </em>among diapsid reptiles, we
 included it in the recently published phylogenetic data matrix of
 Simões et al. 2018. This data set includes the largest taxonomic sampling
 available for early diapsid reptiles, and also includes considerable
 revisions on the construction of morphological characters based on
 discussions provided by [51,52]. This data set contains both a
 morphological and a molecular partition sampled for all of the extant taxa
 included in the data set. Owing to the beneficial effect of removing rogue
 taxa in phylogenetic analysis, especially in the gain in resolution in
 support, we removed two taxa that operate as wildcards in the previous
 version of this data set (<em>Paliguana </em>and
 <em>Pamelina</em>). Not all taxa identified as wildcards were
 removed (e.g. <em>Palaeagama </em>and
 <em>Sophineta</em>), in order to find a balance between
 increase in tree resolution and support versus keeping a taxonomic
 sampling relevant to the questions addressed in the present study. Our
 results consist of morphology only, as well as morphological and molecular
 (combined evidence) analyses. <br>
 <strong>Parsimony analysis</strong>. Analyses are conducted in
 TNT v. 1.155 using the New Technology Search (NTS) algorithms. Tree
 searches are conducted using 1,000 initial trees by random addition
 sequences (RAS) with 100 iterations/round for each of the four NTS
 algorithms: Sectorial Search, Ratchet, Drift and Tree Fusing. The output
 trees are used as the starting trees for subsequent runs, using 1,000
 iterations/rounds of each of the NTS algorithms. The latter step is
 repeated once again, and the final output trees are filtered for all the
 most parsimonious trees (MPTs). <br>
 <strong>Bayesian inference analyses</strong>. Analyses are
 conducted using Mr. Bayes v. 3.2.656. As there are no changes to the
 molecular data set we used, molecular partitions and models of evolution
 are the same as that study. The morphological partition is analysed with
 the Mkv model (given that autapomorphies are included in the data set, but
 there are no invariable characters). Rate variation across characters is
 sampled from a gamma distribution, and analyses used 4 independent runs
 with 6 Markov chains each, sampling at every 1000 generations, for a total
 of 50 million generations. Convergence of independent runs is assessed
 using: average standard deviation of split frequencies (ASDSF ~ 0.01),
 potential scale reduction factors (PSRF ≈ 1 for all parameters) and
 effective sample size (ESS) for each parameter is greater than 200. Leaf
 stability analysis. Leaf stability was assessed using RogueNaRok, which
 allows assessing the difference between the highest and the second highest
 support values for alternative resolutions of each taxon quartet/triplet
 in the data set (LSdif). We applied this method to the posterior trees
 from the Bayesian inference analysis including both morphological and
 molecular data. Because of the large number of taxa and large number of
 trees, it was necessary to downsample the total number of posterior trees
 from each analysis (100,000 trees after discarding burn-in). The final
 sample consisted of 10,000 trees (selecting one at every 10 trees) using
 the Burntrees script for Perl.
description: When using the CT scans provided here, please refer to the
 Staatliches Museum für Naturkunde Stuttgart, as well as to the original
 publication.