New paper, old Chanaresuchus: traditional taxon exclusion issues

A new look at the holotype of Chanaresuchus
by Trotteyn and Ezcurra 2020 provides crisp color photos of the holotype material from several angles, in white light and after µCT scanning.

Unfortunately their small focused cladogram
is a little too small and a little too focused for their taxon list. It might seem large because it includes 115 active taxa from a list of 151 total taxa from (Ezcurra 2016), but, as before, it omits several taxa that would move the thalattosaur, Vancleavea, and the pterosaur, Dimorphodon, out of Archosauromorpha (along with other lepidosaurs like Macrocnemus and Tanystropheus.

Earlier we looked at the many problems in Ezcurra 2016. The largest problem: Ezcurra did not and still does not understand that traditional diapsid taxa are diphyletic and convergent, with some among the Lepidosauria and others starting with Petrolacosaurus and kin within the Archosauromorpha. The Viséan last common ancestor of all reptiles is their last common ancestor.

Earlier we looked at a similar taxon list by Nesbitt 2011 in a 7-part series and demonstrated dozens of scoring errors. After corrections the tree topology came to match the large reptile tree (LRT, 1698+ taxa).

Figure 3. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa.

Figure 1. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa.

From the Trotteyn and Ezcurra 2020 abstract:
“Proterochampsids are one of the several diapsid groups that originated, flourished and became extinct during the Triassic Period. Here we redescribe, figure and compare in detail the holotype of one of these rhadinosuchine species, Chanaresuchus bonapartei from the Chañares Formation. Our new cladistic analyses find stronger support than previous studies for the monophyly of Rhadinosuchinae and the clades that include Doswelliidae + Proterochampsidae and Tropidosuchus + Rhadinosuchinae. Doswelliids are recovered within Proterochampsidae, as the sister taxon to the genus Proterochampsa, in some analyses under implied weights.”

If you find any taxa
in figures 1 and 2 missing from the above list (hint: there are several), those are the taxa Trotteyn and Ezcurra need to add to their next look at proterochampsids.

Figure 2. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

Figure 2. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

References
Ezcurra MD 2016.
The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4, e1778. doi:10. 7717/peerj.1778
Trotteyn MJ and Ezcurra MD 2020. Redescription of the holotype of Chanaresuchus bonapartei Romer, 1971 (Archosauriformes: Proterochampsidae) from the Upper Triassic rocks of the Chañares Formation of north-western Argentina.
Journal of Systematic Palaeontology (advance online publication)
doi: https://doi.org/10.1080/14772019.2020.1768167
https://www.tandfonline.com/doi/full/10.1080/14772019.2020.1768167

https://pterosaurheresies.wordpress.com/2016/04/29/basal-archosauromorpha-paper-ezcurra-2016/

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