A new paper by Schoch and Sues (2013)
introduces a new armored archosauriform with long teeth, Jaxtasuchus salomoni (Fig. 1). It was considered semi-aquatic because it was found in Middle Triassic mudstones along with amphibians, crustaceans, and mollusks. Several incomplete skeletons are known. Schoch and Sues (2013) ran a phylogenetic analysis of 17 taxa that nested Jaxtasuchus with doswelliids, which were similarly armored. Unfortunately, that tree also nested several strange-bedfellows together, including Mesosuchus with Prolacerta, Vancleavea with Chanaresuchus, Parasuchus with Stagonolepis and Scleromochlus with Marasuchus none of whom resemble their putative sisters.
Maybe not a doswelliid
Adding what little is know of Jaxtasuchus to the large reptile tree nests it firmly with Pamelaria, a protorosaur. Protorosaurs are known for their elongated necks, but not for their armor.
In any case, it takes 10 more steps to move Jaxtasuchus to Prolacerta (which was included in the Schoch and Sues (2013) phylogenetic analysis) and 14 steps to move Jaxtasuchus to Doswellia. If valid, the long teeth and armor of Jaxtasuchus would be protorosaur autapomorphies that add new variety to this clade.
A new fifth instance of an antorbital fenestra!
Perhaps even more exciting than armor, Jaxtasuchus was described with an antorbital fenestra lacking a fossa. Doswellia (Heckert et al. 2012) likewise has a tiny antorbital fenestra, but not similar in design. However, a reexamination of Pamelaria reveals a very similar maxilla to Jaxtasuchus, which means it also had a previously overlooked antorbital fenestra (Fig. 2). Together these two up the total number of novel inventions of the antorbital fenestra from four to five. That’s a big deal.
Restoring the manus and pes
I reconstructed the pes and manus of Jaxtasuchus using PILs (parallel interphalangeal lines). On both the manus and pes proximal phalanges were all longer and distal phalanges were all subequal.
The osteoderms have a longer history
The osteoderms of Jaxtasuchus were previously interpreted as coming from temnospondyl amphibians or aetosaurs. Remains of Jaxtasuchus have been found in five localities and have been considered common. Now, courtesy of Schoch and Sues (2013) we know enough about it to consider it an armored predator with an antorbital fenestra. Thanks to the large reptile tree, which includes virtually every basal reptile clade, we can consider Jaxtasuchus a new protorosaur, rather than a doswelliid.
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.
Heckert AB, Lucas SG and Spielmann JA 2012. A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA”. Palaeontology (Blackwell Publishing Ltd) 55 (6): 1333-1348.
Sen K 2003. Pamelaria dolichotrachela, a new prolacertid reptile from the Middle Triassic of India. Journal of Asian Earth Sciences 21: 663–681.
Schoch RR and Sues H-D (2013). A new archosauriform reptile from the Middle Triassic (Ladinian) of Germany. Journal of Systematic Palaeontology (advance online publication) DOI:10.1080/14772019.2013.781066 online