PIMUZ T 2477: not quite Macrocnemus, despite appearances

Updated August 12, 2020
with a new figure 3 which shows the new position of the quadratojugal repaired in figure 2. Apologies for the oversight.

In summary: Miedema et al. 2020 decided not to include
a phylogenetic analysis (e.g. Fig. 1) and so make several mistakes as they describe a µCT scanned specimen (Fig. 2, 3) that turned out to be not quite Macrocnemus (Fig. 1), even though it looks just like one.

Figure 1. Subset of the LRT with the addition of the PIMUZ 2477 specimen.

Figure 1. Subset of the LRT with the addition of the PIMUZ 2477 specimen.

Miedema et al. 2020
take a look at the PIMUZ T 2477 specimen they assigned to Macrocnemus bassani (Figs. 1-4). When added to the large reptile tree (LRT, 1712+ taxa; subset Fig. 1) the PIMUZ T 2477 specimen nested closer to Dinocephalosaurus, next to the clade of Macrocnemus specimens.

Worse yet,
Miedema et al. 2020 promoted a traditional myth, that tanystropheids, like Macrocnemus, were archosauromorphs without testing lepidosaurs. The LRT tests both clades and Macrocnemus nests with lepidosaurs like Huehuecuetzpalli (Fig. 3) despite sharing many convergent traits with the very similar (by convergence) archosauromorph, Prolacerta.

Figure 2. The PIMUZ T 2477 specimen wrongly traditionally assigned to Macrocnemus.

Figure 2. The PIMUZ T 2477 specimen wrongly traditionally assigned to Macrocnemus. Some corrections and repairs  noted. The left maxilla tracing does not match the left maxilla µCT scan.

The palate was restored differently here
than in Miedema et al. 2020 (Fig. 2). So was the prefrontal.

Figure 1. Several Macrocnemus specimens to scale alongside the ancestral taxon in the LRT, Huehuecuetzpalli, and descendant taxa in the LRT, including Cosesaurus and the fenestrasaurs Sharovipteryx, Longisquama and Bergamodactylus. The similarities in transitional taxa should be obvious.

Figure 3. Several Macrocnemus specimens to scale alongside the ancestral taxon in the LRT, Huehuecuetzpalli, and descendant taxa in the LRT, including Cosesaurus and the fenestrasaurs Sharovipteryx, Longisquama and Bergamodactylus. The similarities in transitional taxa should be obvious.

Epipterygoid
“An elongate rod-like element is present underneath the basioccipital and parabasisphenoid in PIMUZ T 2477 (confirming earlier findings here). In this constellation, the rod-like part of the element extends dorsally along the anterior part of the prootic as in all extant Squamata.”

We looked at epipterygoids found in tritosaurs earlier here.

Ontogenetic stage of PIMUZ T 2477
“The smallest specimen, and so far, the only specimen considered a juvenile, MSNM BES SC 111, is slightly smaller in cranial length than PIMUZ T 2477 (ca. 38 mm and ca. 42 mm respectively).”

Not true. Phylogenetic analysis indicates no juveniles are known, only small adults. The BES SC 111 specimen is close to even smaller langobardisaurs, cosesaurs and pterosaurs.

“Juvenile specimens have relatively larger orbits and relatively larger crania compared to adults.”

Not true. Several tritosaurs known from juveniles and adults demonstrate isometric growth.

It is so important to start your study
with a phylogenetic analysis. Lacking an analysis Miedema et al. had no idea that

  1. their specimen did not nest with Macrocnemus
  2. their specimen was closer to Dinocephalosaurus
  3. that all such taxa were lepidosaurs (Peters 2007) in a new clade, the Tritosauria
  4. that no tanystropheids were archosauromorphs
  5. that no known Macrocnemus specimens were juveniles

These are the traditional problems
that come from students following their traditional professors and traditional textbooks, rather than finding out for themselves using phylogenetic analysis. Testing all the specimens as individual taxa is so important as we learned earlier regarding Dorygnathus, Rhamphorhynchus, Pteranodon and many other pterosaurs.

Once again the curse of Chris Bennett
ripples out. Several years ago a rejected paper on the Tritosauria (online at Researchgate.net) could have been cited, but Chris Bennett once told me, “You will never be published, and if you are published, you will not be cited.”

Postscript: 
In March 2020 O’Connor et al. produced a specimen, Oculudentavis, they promoted as an archosauromorph that turned out to be a lepidosaur. This week, under great pressure, the authors retracted their paper. The Miedema authors published the EXACT SAME mistake. Will Miedema et al. have to retract their paper, too? I doubt it. This was not a cover story and there will not be the same sort of pressure on this taxon.


References
Li C, Rieppel O and LaBarbera MC 2004. A Triassic aquatic protorosaur with an extremely long neck. Science 305:1931.
Li Z, Wang W, Hu H, Wang M, Y H and Lu J 2020. Is Oculudentavis a bird or even archosaur? bioRxiv (preprint) doi: https://doi.org/10.1101/2020.03.16.993949
Miedema F, Spiekman1 SNF, Fernandez V, Reumer JWF AND Scheyer1 TM 2020. Cranial morphologyof the tanystropheid Macrocnemus bassanii unveiled using synchrotron microtomography. Nature.com/scientificreports (2020) 10:12412. https://doi.org/10.1038/s41598-020-68912-4
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peyer B 1937. Die Triasfauna der Tessiner Kalkalpen, XII. Macrocnemus bassanii Nopcsa. Abh. Der Schweizierischen Palaeontologischen Gesellschaft LIX (1937).
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

https://www.researchgate.net/publication/328388754_A_new_lepidosaur_clade_the_Tritosauria

https://www.nature.com/articles/s41598-020-68912-4#article-comments

wiki/Oculudentavis
wiki/Dinocephalosaurus
wiki/Macrocnemus