The origin of the Parasuchia

Parasuchians (phytosaurs) are those very croc-like Triassic swamp giants with a nostril rising on a bony volcano almost between their eyes (Fig. 1).

A selection of phytosaurs (parasuchians).

Figure 1. A selection of phytosaurs (parasuchians).

Parasuchians all have a similar appearance. 
The question is, where did they come from? Which taxa are their closest ancestors?

Nesbitt (2011) 
nested parasuchians between Euparkeria and Archosauria (Ornithodira (including pterosaurs) + pseudosuchia. Apparently it didn’t matter to Nesbitt’s study that his parasuchians didn’t resemble the most closely nested taxa.

Brusatte et al. (2010)
nested parasuchians between Proterochaampsidae and Aetosauria + the rest of the Pseudosuchia; or (when pterosaurs were removed) between Revueltosaurus and Aetosauria + the rest of the Pseudosuchia. In both cases the Avemetatarsalia (pterosaurs + dinosaurs and kin) were considered closely related. So again, not many taxa here display a gradual accumulation of parasuchian traits.

According to the large reptile tree
everything becomes much more clear and a gradual accumulation of parasuchian traits is clearly visible in ancestral taxa (Fig 2).

Figure 2. The origin of the Parasuchia (Phytosauria) with Diandongosuchus, Mesorhinosuchus and related taxa.

Figure 2. The origin of the Parasuchia (Phytosauria) with Diandongosuchus, Mesorhinosuchus and related taxa. This series demonstrates a gradual accumulation of parasuchian traits. It would be nice to find one with the nostrils midway on the snout.

Taxon inclusion is key to this understanding. Using specimens rather than suprageneric taxa is also important.

References
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

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