Omphalosauridae: a new definition for a 1906 clade

Qiao et al 2022 report,
“Omphalosauridae, comprising several species in the genus Omphalosaurus, is an enigmatic group of durophagous marine reptiles known hitherto from Early–Middle Triassic pelagic sediments of Western North America, Svalbard, and the Bavarian Alps”.

The authors make the following citations:
“Omphalosauridae Merriam, 1906 (= Nasorostra Jiang et al., 2016)”. The authors nest this clade within the Ichthyosauriformes and within the Ichthryosauriformes within the clade Diapsida.

Qiao et al define Omphalosauridae (Merriam 1906) as:
“The last common ancestor of Omphalosaurus nevadanus, Cartorhynchus lenticarpus and Sclerocormus parviceps and all of its descendants.”

In the LRT (Fig 3) that last common ancestor is Claudiosaurus, a marine younginiform. “All descendants” in the LRT include sauropterygians, ichthyosaurs, mesosaurs, thalattosaurs and the omphalosaur clade, which is not the authors’ intent. Basically this new clade definition is Enaliosauria + Claudiosaurus and the Omphalosaurus clade slips in between them. That’s OK.

Taxon exclusion mars this report.
At least two clades of unrelated taxa have a diapsid skull in the large reptile tree (LRT, 2173 taxa). Qiao et al did not know this. Ichthyosaurs nest with Sauropterygia within the Enaliosauria. Qiao et al are not aware of this. That’s why adding taxa is so important. Cherry-picking taxa leads to false positives.

In the LRT
Omphalosaurus nests in a clade basal to the Enaliosauria (Fig 3). Other clade members include Atopodentatus, Sinosaurosphargis, Largocephalosaurus. The proximal outgroup taxon is Claudiosaurus. Only two of these were mentioned and tested in the Qiao et al analysis: Sinosaurosphargis and Largocephalosaurus.

The authors mistakenly consider
Sclerocormus and Cartorhynchus to be members of the Ichthyosauriformes. Adding taxa moves both to the base of the Sauropterygia close to Qianxisaurus, yet another taxon missing from the authors’ analysis.

References
Qiao Y et al (7 co-authors) 2022. A globally distributed durophagous marine reptile clade supports the rapid recovery of pelagic ecosystems after the Permo-Triassic mass extinction. Nature communications biology https://doi.org/10.1038/s42003-022-04162-6