Litorosuchus phylogeny revised

Figure 1. Litorosuchus somnii was wrongly considered a sister to Vancleavea and wrongly considered an archosauriform. In the LRT it nests with Macrocnemus, a tritosaur lepidosaur that also has members with an antorbital fenestra. Click to see an enlarged rollover image.

Figure 1. Litorosuchus somnii was wrongly considered a sister to Vancleavea, which was wrongly considered an archosauriform. In the LRT Litorosuchus nests with Jaxtasuchus, a protorosaur, which was also wrongly considered an archosauriform, that also has an antorbital fenestra. Click to see an enlarged rollover image. (See figure 2).

Earlier we looked at
Litorosuchus (Fig. 1,2; Li et al. 2016; Middle Triassic; 2m in length), an armored aquatic protorosaur (previously mis-nested in the large reptile tree (LRT, 1327 taxa) as an armored, aquatic macrocnemid). The recent work on the various specimens attributed to Macrocnemus raised red flags on Litorosuchus, which did not quite fit the elusive, but required ‘gradual accumulation of traits’ that tells you your phylogenetic analysis reflects actual events in evolution.

Protorosaurs and macrocnemids
have been traditionally confused with one another and wrongly linked together due to their many convergent traits. The former is a member of the new Archosauromorpha. The latter belongs to the new Lepidosauromorpha.

Figure 2. Litorosuchus in situ with a new tracing of the inverted and displaced posterior premaxilla with several teeth.

Figure 2. Litorosuchus in situ with a new tracing of the inverted and displaced posterior premaxilla with several teeth.

Some re-scoring led to a re-nesting
of Litorosuchus with an incompletely known aquatic armored protorosaur also with an antorbital fenestra, Jaxtasuchus (Fig. 3; Schoch and Sues 2012; Middle Triassic; originally wrongly considered a Doswellia relative due to taxon exclusion; estimated length: 70-80cm).

Figure 2. The armored aquatic protorosaur, Jaxtasuchus, is smaller and less complete than Litorosuchus.

Figure 3. The armored aquatic protorosaur, Jaxtasuchus, is smaller and less complete than Litorosuchus.

Only a few scored traits differ
in Litorosuchus and Jaxtasuchus. Only a few related protorosaurs share an antorbital fenestra, developed by convergence with various chroniosuchid macrocnemid, fenestrasaurYoungina, Youngoides and archosauriform taxa.

Apologies
for the earlier mistake. Reexamination (= testing) is just one of the many processes of science. That often happens here, but a bit rare out there in the world of paleontology.

References
Li C, Wu X-C, Zhao L-J, Nesbitt SJ, Stocker MR, Wang L-T 2016. A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria. The Science of Nature 103: 95. doi:10.1007/s00114-016-1418-4
Schoch and Sues 2012. A new archosauriform reptile from the Middle Triassic (Ladinian) of Germany. Journal of Systematic Palaeontology, 2013. http://dx.doi.org/10.1080/14772019.2013.781066

wiki/Prolacertiformes
wiki/Protorosauria
wiki/Jaxtasuchus
wiki/Litorosuchus

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