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.
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.
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),
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.
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