Late Triassic Kwanasaurus: another poposaur close to Silesaurus

…but only in the LRT.
There is no reference to the Poposauria (Fig. 2) in the Martz and Small 2019 text. They describe their new taxon, Kwanasaurus wiliamparkeri (Fig. 1), known from scattered bits and pieces from young and old individuals, and nest it with Silesaurus (Fig. 2). The authors consider Silesaurus a dinosauromorph.

By contrast
in the large reptile tree (LRT, 1566 taxa; subset Fig. 3) the clade Dinosauromorpha is a junior synonym for Archosauria because only crocs and dinos make up the Archosauria. This recovery is distinct from all other studies that suffer from taxon exclusion and poor scoring.

FIgure 1. Large image from Martz and Small 2019. Small image scaled using scale bars. Dark image slightly modified to fit ilium length, humerus, etc.

FIgure 1. Large image from Martz and Small 2019. Small image scaled using scale bars. Dark image slightly modified to fit ilium length, humerus, etc.

The authors report:
“We have opted to utilize the data matrix of Peecook et al. (2013), acquiring the Nexus file from Morphobank. The matrix of Peecook et al. (2013) is slightly modified from the matrix of Nesbitt et al. (2010).” Earlier in a 7-part series we looked at scoring problems with Nesbitt inspired cladograms.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Figure 2. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

In the LRT
(subset Fig. 3) the clade Poposauria (including Silesaurus and kin) nest as the first outgroup to the Archosauria. So dinosaurs and polosaurs are very close, as everyone agrees. Just keep adding taxa, especially basal bipedal crocs, to fine tune the tree topography.

Figure 5. Subset of the LRT focusing on the Poposauria and surrounding clades.

Figure 3. Subset of the LRT focusing on the Poposauria and surrounding clades.

Here’s a cladogram from Martz and Small 2019
(Fig. 4) missing many pertinent taxa and including five irrelevant taxa, like pterosaurs and lagerpetids (proterochampsids). That and a raft of bad scores mess things up as demonstrated by the lack of similarity between putative sister taxa below. There is no such problem in the LRT (Fig. 3) where microevolution is documented between sisters.

Figure 6. Three cladograms from Martz and Small 2019 nesting Kwanasaruus with silesaurids.

Figure 4. Three cladograms from Martz and Small 2019 nesting Kwanasaruus with silesaurids. Yellow green are poposaur in the LRT. Yellow tint are dinosaurs in the LRT. Brown are lagerpetids in the LRT. Gray are lepidosaur pterosaurs in the LRT. 

References
Martz JW and Small BJ 2019. Non-dinosaurian dinosauromorphs from the Chinle Formation (Upper Triassic) of the Eagle Basin, northern Colorado: Dromomeron romeri (Lagerpetidae) and a new taxon, Kwanasaurus williamparkeri (Silesauridae).
PeerJ 7:e7551 DOI 10.7717/peerj.7551

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