Revisiting Yonghesuchus: now a sister to Litargosuchus

Those two wide, low (flat) skulls should have been a dead-giveaway
linking Yonghesuchus (Fig. 1) to Litargosuchus (Fig. 2). One problem is: Yonghesuchus lacks skull roofing bones.

Figure 1. The skull of Yonghesuchus now compares well with that of Litargosuchus (figure 2).

Figure 1. The skull of Yonghesuchus now compares well with that of the slightly smaller Litargosuchus skull (figure 2).

Using phylogenetic bracketing
to restore large bulbous squamosals in Yonghesuchus, as in Litargosuchus, helps one realize the probable extent of loss of bone in this specimen, all other aspects being similar.

Figure 2. Litargosuchus with skull enlarged in 3 views. The Yonghesuchus skull is slightly larger than this one.

Figure 2. Litargosuchus with skull enlarged in 3 views. The Yonghesuchus skull is slightly larger than this one.

After a recent review of the Crocodylomorpha in the LRT,
several taxa, including Yonghesuchus, have moved around the cladogram. Some taxa were initially and naively nested several years ago and not looked at since. After the addition of dozens of taxa, new insights drive these changes. The difficulties are compounded by fossils with more cracks than sutures and other taphonomic jumbles.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 3. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Yonghesuchus sangbiensis (Wu, Liu and Li 2001) was the first tetrapod discovered from the Late Triassic of China. The presence of pterygoid teeth was thought to preclude membership within the Archosauria despite a suite of traits to the contrary. Here Yonghesuchus nests with flat-headed Litargosuchus within the Archosauria and within the Crocodylomorpha. The presence of pterygoid teeth is a reversal perhaps due to its very flattened skull and wide gape. The maxillary teeth were angled posteriorly. The antorbital fenestra was relatively large. The amphicoelus cervical vertebrae were elongated with ribs on elongated stems as in Dromicosuchus.

Litargosuchus leptorhynchus (Clark and Sues 2002; Late Triassicl; BP/1/5237) was a bipedal basal crocodylomorph from South Africa in the lineage of living crocs. It was derived from a sister to Terrestrisuchus and Erpetosuchus. Clark and Sues were unable to resolve their family tree, but they did not include three of the four above taxa

Butler et al. 2014 
suggested a sister group relationship between Gracilisuchus, Yonghesuchus and Turfanosuchus. In the LRT (Fig. 4) these three taxa are still not sisters. Several taxa intervene between every paired relationship suggested by these authors.

Figure 4. Terrestrisuchus nests basal to Yonghesuchus and Litargosuchus in the LRT.

Figure 4. Terrestrisuchus nests basal to Yonghesuchus and Litargosuchus in the LRT. This taxon displays the origin of the round squamosal. 

Speculation:
Like Litargosuchus, Yonghesuchus, was also a long-limbed, based on phylogenetic bracketing. Long-limbed quadrupedal Terrestrisuchus (Fig. 4) was a quadruped.


References
Butler RJ, Sullivan C, Ezcurra MD, Liu J, Lecuona A and Sookias RB 2014.New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evolutionary Biology 14:1-16.
Clark JM and Sues H-D 2002. 
Two new basal crocodylomorph archosaurs form the Lower Jurassic and the monophyly of the Sphenosuchia. Zoological Journal of the Linnean Society 136:77-95.
Wu X-C, Liu J and Li J-L 2001. The anatomy of the first archosauriform (Diapsida) from the terrestrial Upper Triassic of China. Vertebrata PalAsiatica39:251-265.

wiki/Litargosuchus
wiki/Yonghesuchus

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