Diandongosuchus palate

Diandongosuchus fuyuanensis was originally (Li et al. 2012) nested with Qianosuchus and the poposaurids, but it shares very few traits with these taxa as blogged here. This middle Middle Triassic, croc-mimic was derived from a croc-like specimen of Youngina, BPI 2871 and a sister to Diandongosuchus gave rise to the parasuchians, Paleorhinus and Parasuchus. Proterochampsa was a sister and Diandongosuchus is not far from long-legged Chanaresuchus and Doswellia + Choristodera.

We looked at Diandongosuchus earlier here and in five other posts.

The palate is virtually invisible (Fig. 1), seen only through the naris, antorbital fenestra, orbit and a smidgeon between the jaws on the underside. The basisphenoid is not visible, probably hidden beneath a mandible. But the cultriform process is visible. So, with available data, here is the palate of Diandongosuchus reconstructed in a step-by-step process using the infamous DGS (digital graphic segregation), which I submit, still has value as shown below.

Figure 1. Using DGS to tease out the palate elements of Diandongosuchus. Color tracings enable the important elements of the skull to be layered upon one another to see where things match up and where they don’t. A sliver here might be connected to another sliver there. I was surprised to see how narrow the skull was, even before crushing.

Diandongosuchus is just another big, nasty, robust younginid, but developing along separate lines than Proterosuchus and Garjainia, which have a similar heritage. Converging with Gargainia, the skull of Diandongosuchus was taller than wide, which is different than all of its closest sisters.

The deep cheeks in this taxon are further developed in parasuchians, which raised the orbit to the top of the skull. The vomers are very long and I suspect that the maxillary palatal plates supported it. You can see rather plainly in Chanaresuchus, in which the internal nare are divided into fore and aft openings by the advancing maxilla. In parasuchia the vomer is very short because the premaxilla is very long.

References
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

wiki/Diandongosuchus

Proterochampsia Paper

David Dilkes was kind enough to send his new paper on Proterochampsa (Dilkes and Arcucci 2012). His tree follows traditional nestings (Fig. 1). Dilkes and Arcucci (2012) also describe the long journey this odd branch has taken as new taxa were slowly added over the years. Makes interesting reading.

Figure 1. Proterochampsia tree by Dilkes and Arcucci (2012). Green added to highlight relationships recovered by the large reptile tree (Fig. 2). Some notes added in blue and red highlight missing and “by default” taxa that should not be included. Not sure why parasuchians don’t nest closer to proterochampsids here as they often do in other trees, including the large reptile tree. Euparkeria seems out of place there, but does nest close to Riojasuchus in other trees.

Unfortunately, one again, too few taxa were added to this tree to recover the same relationships recovered by the large reptile tree (Fig. 2) in which all sister taxa share larger suites of traits. In the Dilkes and Arcucci (2012) tree you get such odd pairings as Doswellia and Vancleavea, Riojasuchus and Aetosaurus, Euparkeria and Parasuchus among others. Only the taxa within the focus group, the Proterochampsia (node D), are true sisters also recovered by the large reptile tree.

Wisely, Dilkes and Arcucci (2012) left out pterosaurs, which are often nested close to parasuchians and proterochampsids. Unfortunately they left out Lagerpeton, members of the Choristodera and several Youngina/Youngoides specimens, all of which would have helped clarify relationships, according to the large reptile tree.

Figure 2. Left: A segment of the large reptile tree showing what happens when more taxa are included. The Pararchosauriformes form a branch separate from the Euarchosauriformes and develop an antorbital fenestra and foss by convergence. Right: Reducing the branch on the left to include only those taxa chosen by Dilkes and Arcucci (2012) with the addition of the thalattosaur, Vancleavea, mistakenly chosen for inclusion by Dilkes and Arcucci (2012). Here more parsimony in sister taxa, but several forced nestings further toward the base of the tree.

A segment of the large reptile tree (Fig. 2) recovers a different topology because more taxa are included. In the large reptile tree the Proterochampsia were more closely related to parasuchians and choristoderans. All share a dorsal, posteriorly-displaced naris (reversed in Champsosaurus as a snorkel), and several other synapomorphies.

A Distinct Convergent Antorbital Fenestra
We discussed earlier the four times the antorbital fenestra was developed. Check it out. We also earlier discussed the nesting of the large proterochampsid (Fig. 3),

Figure 3. A new specimen attributed to Proterochampsa alongside the holotype specimen.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Dilkes D and Arcucci A 2012. Proterochampsa barrionuevoi (Archosauriformes: Proterochampsia) from the Late Triassic (Carnian) of Argentina and a phylogenetic analysis of Proterochampsia.  Palaeontology (advance online publication) 1-33. doi: 10.1111/j.1475-4983.2012.01170.x

A New Proterochampsa? This Time with Postcrania!

For several decades all we knew of Proterochampsa barrionuevoia (Reig 1959) consisted of several skulls and cervical vertebrae. The rest of the postcranium remained unknown until now. A new report by Trotteyn (2011) reveals much of the missing post-crania. PVSJ 606 was at least twice as large as the holotype (Fig. 1). It was found in the Ischigualisto Formation of the Late Triassic.

Figure 1. A new specimen (PVSJ 606) attributed to Proterochampsa by Trotteyn (2011). Lateral view from Trotteyn (2011). Dorsal view after tracing the skull image in Trotteyn (2011).

Proterochampsa nodosa
A third specimen and a separate species, P. nodosa, I have not seen yet. The abstract distinguishes the two species, “..snout becoming narrow anteriorly in a less gradual manner than in P. nodosa, lower occiput, nares lanceolate with narrow anterior and posterior ends, and frontal less irregular that in P. nodosa.”

Figure 2. Bone identification in a dorsal view of the skull PVSJ 606.

Comparisons
Due to the compressed skull of PVSJ 606 and its attribution, I expected the post-crania to be likewise compressed with short legs, perhaps most similar to basal parasuchians, like Parasuchus. As it turns out, the post-crania more closely resembled that of Chanaresuchus.

Figure 3. The Pararchosauriformes. Click to see entire tree. Note the nesting of the new specimen attributed to Proterochampsa as a sister to the holotype, but at the base of the chanaresuchids.

Description
The skull of PVSJ 606 (Fig. 2) was relatively enormous! It was as long as the presacral vertebral column. The various fenestrae were relatively smaller. The premaxilla was shorter and the post-orbital area was more robust. The premaxilla was not squared off. Do these differences, plus the major size difference mean the new specimen is a new species? Unfortunately Trotteyn (2011) completely ignored comparisons to the holotype skull, focusing all her efforts on a description of the post-crania alone.

The cervicals and caudals were more gracile in PVSJ 606 than in sister taxa. This seems improbable considering the size of the skull, but true. The torso was rather short and the legs were rather long.

Ecology and Behavior
No one has figured out the ecology and behavior of Proterochampsa or this specimen. Not sure what to make of it yet. It’s a bizarre creature!

Analysis
Trotteyn (2011) did not published a cladistic analysis having opted instead to synonymize the new specimen with the holotype of Proterochampsa. Under cladistic analysis PVSJ 606 nested as a sister to Proterochampsa (Fig. 3) at the base of the Cerritosaurus clade that also includes Chanaresuchus. So, PVSJ 606 is likely not congeneric or conspecific with Proterochampsa. It takes 8 extra steps to create a sisterhood with the holotype.

Figure 4. DGS reveals two other digits and metatarsal 5 not described in the pes of Proterochampsa hidden among the skull bones. See Figure 1 for a reconstruction.

The Pes
Only two toes (including their metatarsals) were described by Trotteyn (2011). Examination of the photograph (Fig. 2) appears to show two more toes plus metatarsal 5 on the skull, which is somewhat fragmented, but largely intact. The  reconstructed elements create what appears to be a valid pes with continuous PILs (Fig. 1). Are these interpretations valid or not? Send data! We’ll figure this out. I’m only working from published photos in black and white.

An Ancestral Sister to Pterosaurs and Dinosaurs?
A recent report on archosaur relations (Brusatte et al. 2010) placed Proterochampsa at the base of the clade that produced dinosaurs and pterosaurs. Ridiculous for dozens of reasons, yet this was one of many such studies with similar results. Unsupportable and illogical results such as these are a direct result of inappropriate exclusions and inclusions in the taxon list resulting in “by default” nestings.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

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.
Reig OA 1959 Primeros datos descriptivos sobre nuevos Reptiles Arcosaurios del Triasico de Ischigualsto (San Juan, Argentina): Revista de la Asociacion Geologica Argentina, tomo 13, n. 4, p. 257-270.
Trotteyn MJ 2011. Material postcraneano de Proterochampsa barrionuevoi Reig, 1959 (Diapsida: Archosauriformes) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 48:424-446.

wiki/Proterochampsa