CM 73372 reconstructed

So far as I know,
Carnegie Museum specimen CM 73372 (Fig. 1) does not yet have a name, nor has it been reconstructed. Weinbaum 2013 included this skull-less image in a Postosuchus study, which makes sense at first sight, given the size, proportions and age (Late Triassic) of both specimens. The large reptile tree (LRT, 1394 taxa) nests CM73372 close to Postosuchus, but closer to Teratosaurus and Smok. Since Teratosaurus is known from skull-only data at present, there is loss of resolution at that node.

Figure 1. CM73372 in situ and reconstructed using DGS methodology. At first glance it seems to be a biped with short fingers, like Postosuchus. In situ image from Weinbaum 2013.

Figure 1. CM73372 in situ and reconstructed using DGS methodology. At first glance it seems to be a biped with short fingers, like Postosuchus. In situ image from Weinbaum 2013.

This is an interesting taxon because
Lucuona et al. 2017 and others nest it basal to Crocodylomorpha. Weinbaum considered it a member of the Archosauria and the Paracrocodylomorpha, a clade the large reptile tree (LRT, 1394 taxa) does not recover.

According to Wikipedia
Loricata was an early name for an order that includes crocodilesalligators, and gharials, although the order is now referred to as Crocodylia. Nesbitt 2011 defined it as the most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not the extinct Poposaurus gracilisOrnithosuchus longidens, or Aetosaurus ferox. In the LRT, that clade is a junior synonym for Crocodylomorpha, since Poposaurus is a member of the proximal outgroup, the Poposauria. In traditional paleontology Loricata includes Rauisuchia and Crocodylomorpha. If so, then it also includes Poposauria and Dinosauria, but that was not the original intention of this definition.

Paracrocodylomorpha is another clade invalidated by the LRT because it includes Poposauria and Loricata. In the LRT Rauisuchia is the basal clade, followed roughly by Poposauria and Archosauria (crocs + dinos only).

You might recall,
the Nesbitt 2011 cladogram finds phytosaurs arising from a sister to the distinctly different Euparkeria. Taxon exclusion is the problem here. Nesbitt 2011 also finds Ornithosuchia (Ornithosuchus and kin) and Pterosauria forming the first dichotomy arising from a basal sister to Phytosauria. Again taxon exclusion is the problem here, yet widely accepted in the paleo community for reasons unknown (except, possibly ease of use and fear of change). We talked about other odd and topsy-turvy sister taxa recovered by Nesbitt 2011 earlier here, here and here, three blog posts in a nine-part series.

This addition of CM73372 to the LRT sets us up
for tomorrow’s discussion on basal archosaurs.

Lecuona A, Desojo JB and Pol D 2017. New information on the postcranial skeleton of Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position. Zoological Journal of the Linnean Society, 2017, XX, 1–40.
Weinbaum J 2013. Postcranial skeleton of Postosuchus kirkpatricki (Archosauria:
Paracrocodylomorpha), from the Upper Triassic of the United States. Geological Society London Special Publications · August 2013.


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