Ezcurra and Sues play the taxon exclusion gambit with Sphodrosaurus and fail several times

From the Ezcurra and Sues abstract:
“Most Triassic terrestrial diapsids belong to two clades, Lepidosauromorpha or (the more diverse) Archosauromorpha.”

The authors have it backwards. One clade of diapsids nests within Lepidosauromorpha in the large reptile tree (LRT, 2089 taxa). The other clade of convergent diapsids nests within Archosauromorpha. Taxon inclusion resolves all such issues.

“Nevertheless, the phylogenetic relationships of some Triassic diapsids have remained uncertain for decades because of the lack of preservation of phylogenetically relevant anatomical regions or because of unusual combinations of features.”

The authors are ten years too late. The phylogenetic relationships of all Triassic diapsid-grade taxa tested in the LRT are completely resolved.

This is incorrect due to taxon exclusion. Long and narrow Doswellia is related to the SAMPKK 10603 specimen attributed to Proterosuchus. A few nodes apart, proterochampsids arise from Diandongosuchus and kin in the LRT.

Colleagues: Build your own LRT. Then mistakes like this won’t happen.

“Previous authors recognized that the most unusual feature of Sphodrosaurus pennsylvanicus is its proportionally very large skull.

Ezcurra and Sues are “Pulling a Larry Martin.” As you can see, this unscientific practice reaches the highest levels in this paper. Test more taxa to avoid this mistake.

“Phylogenetic generalized least squares regressions confirmed that Sphodrosaurus pennsylvanicus has a larger skull than the vast majority of Permo–Triassic diapsids. Optimization in the phylogeny of the skull width to presacral length ratio shows the most likely scenario is that the extremely broad skull of Sphodrosaurus pennsylvanicus is autapomorphic, but it is not unique among archosauromorphs, being paralleled by hyperodapedontine rhynchosaurs and the proterochampsian Proterochampsa barrionuevoi.”

“The most likely scenario…” When you find yourself typing those words into your manuscript realize that you have now left the realm of science and are entering the realm of speculation.

“Autapomorphic…” When you find yourself typing those words into your manuscript realize that you are looking at exactly the wrong taxa as candidate sisters. Look elsewhere. In evolution nothing is autapomorphic, except when excluding pertinent taxa.

Rhynchosaurs are not archosauromorphs in the LRT.

Lacking their own LRT, Ezcurra and Sues are stumbling around in a dark room, cherry-picking taxa to nest their favorite enigmas and failing again and again due to taxon exclusion.

3m long Proterochampsa does have an enormous skull. That skull is as long as the pre-sacral length. That’s not the case with 24cm long Sphodrosaurus (Fig 1) with a much smaller skull and shorter, wider torso, twice as wide as the skull, as in Sclerosaurus (Fig 4).

“Exploration of a morphospace of linear measurements shows that Sphodrosaurus pennsylvanicus shares strong similarities with the probably semi-aquatic Proterochampsa barrionuevoi, suggesting that the former species may have had a similar mode of life.

Compare Sphodrosaurus to its closest relatives in the LRT (Figs 3, 4). That makes tiny Sphodrosaurus a phylogenetically miniaturized taxon at the genesis of soft-shelled turtles, a late-surviving precursor to a coeval Late Triassic Odontochelys.

Ezcurra and Sues report,
“The new data set is composed of 190 active terminals and 887 active characters.”
It would have been better the other way around. The LRT tests 2089 taxa (= active terminals). Only two included taxa in the Ezcurra and Sues study were lepidosauromorphs, Marmoretta and Huehuecuetzpalli. No turtles or pareiasaurs are mentioned in the text, either.

Ezcurra and Sues nest Sphodrosaurus
(their figure 10) at the base of a clade that includes Jaxtasuchus, then Doswellia + Rugarhynchos. These nested not far from Vancleava + Litorosuchus in their study.

By contrast in the LRT Jaxtasuchus and Litorosuchus nest together as elongate armored protorosaurs derived from elongate unarmored Malerisaurus, a taxon deactivated by Ezcurra and Sues. Vancleavea nests with thalattosaurs when thalattosaurs are included in the taxon list. Rugarhynchos is a former Doswellia sp., so someone thought they were congeneric at one time. Don’t exclude or deactivate taxa or you’ll end up with a similar mess.

Ezcurra and Sues report,
“We thank the reviewers Stephan Spiekman and Brenen Wynd and the editor Richard Butler for their suggestions and comments.”

These esteemed workers also share blame for letting this study reach publication without requiring the inclusion of competing candidate taxa known since 2018 and suspected since Rice et al. 2016.

References
Colbert EH 1960. A new Triassic procolophonid from Pennsylvania. American Museum Novitates 2022:1–19.
Ezcurra MD and Sues H-D 2022. A re-assessment of the osteology and phylogenetic relationships of the enigmatic, large-headed reptile Sphodrosaurus pennsylvanicus (Late Triassic, Pennsylvania, USA) indicates archosauriform affinities. Journal of Systematic Palaeontology. 0 (0): 1–35. doi:10.1080/14772019.2022.2057820
Meyer H von 1859. Sclerosaurus armatus aus dem bunten Sandestein von Rheinfelsen. Palaeontographica 7:35-40.
Rice R, Kallonen A, Cebra-Thomas J and Gilbert SF 2016. Development of the turtle plastron, the order-defining skeletal structure. PNAS 113 (19):5317–5322.
Sues H-D, Baird D and Olsen PE 1993. Redescription of Sphodrosaurus pennsylvanicus Colbert, 1960 (Reptilia) and a Reassessment of its Affinities. Annals of Carnegie Museum 62(3):245-253.
Sues H-D and Reisz RR 2008. Anatomy and Phylogenetic Relationships of Sclerosaurus armatus (Amniota: Parareptilia) from the Buntsandstein (Triassic) of Europe. Journal of Vertebrate Paleontology 28(4):1031-1042. doi: 10.1671/0272-4634-28.4.1031 online

wiki/Arganaceras
wiki/Sclerosaurus
wiki/Sphodrosaurus
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