Luopingosaurus looks like a pachypleurosur, but like Honghesaurus is basal to mesosaurs, thalattosaurs and ichthyosaurs

Li et al 2023 reported,
“Phylogenetic studies incorporating Luopingosaurus recover European pachypleurosaurids as successive sister groups to Chinese derived pachypleurosaurids, supporting a western Tethyan origin for this family.”

Luopingosaurus looks like a pachypleurosaur, but is it one? Let’s find out.

Unfortunately,
taxon exclusion mars the otherwise excellent description of this new taxon (Fig 1). In the large reptile tree (LRT, 2199 taxa) Luopingosaurus is a sister to the Sauropterygia, not a member. That’s why they look so much alike. Middle Triassic Luopingosaurus is a late surviving taxon of an Early Permian marine radiation. In the LRT Luopingosaurus is ancestral to Honghesaurus, then Mesosauria + Thalattosauria, then Wumengosaurus and then Ichthyosauria and kin. This is a more important taxon than the authors understand it to be. Key taxa should not be omitted.

Earlier
closely related Honghesaurus nested at this same basal node. That was reported here in May 2022. Li et al also tested Serpianosaurus as a pachypleurosaur. Adding taxa nests Serpianosaurus as a basal thalattosaur in the LRT.

Li et al reported,
“Outside of pachypleurosauroids, a similarly anteriorly pointed snout associated with an elongate trunk is otherwise present in some thalattosaurs, and this likely represents
convergent adaptation driven by similar feeding and swimming mechanics.”

“Likely represents” = guessing. Why not test this possibility by adding thalattosaurs to your own cladogram? Unfortunately reticence like this is what separates paid professionals from independent researchers nowadays. Mesosaurs are not mentioned in the Li et al text despite their morphological similarity and phylogenetic proximity in the LRT.

References
Xu G-H et al (7 co-authors) 2023. A new long-snouted marine reptile from the Middle Triassic of China illuminates pachypleurosauroid evolution. Nature Scientific Reports 13:16 https://doi.org/10.1038/s41598-022-24930-y

wiki/Luopingosaurus– not yet posted
wiki/Honghesaurus