Tiny Vellbergia: a juvenile Prolacerta, not a stem-lepidosauromorph

Sobral, Simoes and Schoch 2020
report on a new, tiny, Middle Triassic reptile, Vellbergia bartholomei (Figs. 1, 3) known from disarticulated skull material. Without creating a reconstruction, they considered Vellbergia a stem-lepidosauromorph different from other stem-lepidosauromorphs.

Figure 1. Vellbergia in situ, original line drawing, DGS colors apple and reconstruction. Note the quadrate break occurs during taphonomic crushing of the curved bone. Scale bar = 5mm. So the skull is about 1.5cm in length, quite tiny.

Figure 1. Vellbergia in situ, original line drawing, DGS colors apple and reconstruction. Note the quadrate break occurs during taphonomic crushing of the curved bone. The nasal, frontal and parietals are incomplete due to their juvenile state. Scale bar = 5mm. So the skull is about 1.5cm in length, quite tiny.

The authors report:
“Important morphological attributes of Vellbergia, most notably the elongate and slender jaw bones, the deeper post-dentary region of the jaw relative to the anterior region, and the far posteriorly reaching maxillary tooth row can be found on some other early diverging diapsid species, such as Prolacerta and Youngina, thus showing these features were retained into the early part of the lepidosauromorph evolutionary history as well.”

Prolacerta.

Figure 2. Prolacerta. Note the relative lengths of the manual and pedal lateral digits.

After phylogenetic analysis
in the large reptile tree (LRT, 1653+ taxa) Vellbergia nests with Prolacerta (Figs. 2, 3). A reconstruction (Figs. 1, 3) demonstrates a close affinity. Based on size and the smooth, incomplete, open sutures of the specimen, this is a juvenile. So the genus ‘Vellbergia’ is a junior synonym. The authors did not include Prolacerta in their published cladogram, but did list it in their suppdata.

Figure 3. Prolacerta and 'Vellbergia' to scale.

Figure 3. Prolacerta and ‘Vellbergia’ to scale.

Taxon exclusion
The Sobral, Simoes and Schoch taxon list did not include enough taxa to produce the basal dichotomy splitting Archosauromorpha from Lepidosauromorpha in the Viséan following their last common ancestor, Silvanerpeton. Prolacertiformes (= Protorosauria) nest in the Archosauromorpha and converge with Lepidosauriformes in many ways, hence the traditional confusion.

The LRT is available online.
Problems like this can be avoided by using ReptileEvolution.com and the LRT to double-check work before submission.


References
Sobral G, Simoes TR and Schoch RR 2020.
A tiny new Middle Triassic stem-lepidosauromorph from Germany: implications fro the early evolution of lepidosauromorphs and the Vellberg fauna. Nature.com Scientific Reports 10, Article number: 2273.

https://doi.org/10.1038/s41598-020-58883-x
https://www.nature.com/articles/s41598-020-58883-x

 

 

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