A new basal archosauriform from the Middle-Late Triassic of Brazil and the monophyly of Doswelliidae

DESOJO, J. B.; EZCURRA, M. D.; SCHULTZ, C. L.

San Luis

Jornada; XXV JORNADAS ARGENTINAS DE PALEONTOLOGÍA DE VERTEBRADOS; 2010

We describe herein a new archosauriform specimen collected from the lower levels of the Santa Maria Formation (Middle-Late Triassic) of southern Brazil (CPEZ 239a). It is based on a basicranium, dorsal and sacral vertebrae, ten paramedian andthree lateral osteoderms, and right humerus, ulna, ilium, ischium, femur, and tibia. A cladistic analysis was conducted andnested CPEZ 239a within a monophyletic group of basal archosauriforms, also composed of Doswellia from the LateTriassic of USA and Tarjadia from the Middle-Late Triassic of Argentina. This group is identified as Doswelliidae and it issupported by the presence of coarse, incised osteoderm ornamentation composed of regular pits of equal size and contour,and the presence of an un-ornamented anterior articular bar. In addition, CPEZ 239a is more closely related to Doswelliathan to other archosauriforms due to the presence of antero-laterally oriented basipterygoid processes, dorsal vertebra centrawith convex lateral surfaces, width of the neural arch plus ribs of the first sacral three times the length of the neuralarch, and iliac blade laterally deflected, with a strongly convex dorsal margin, and a maximum length less than 3 times itsmaximum height. Since Doswelliidae was previously considered a monospecific clade, this study supports for the firsttime its validity and incorporates it to the traditionally known lineages of basal archosauriforms (e.g. Proterosuchidae,Erythrosuchidae, Proterochampsidae). The present phylogenetic analysis indicates that Doswelliidae is the closest largemonophyletic entity to Archosauria, attaining a wide paleolatitudinal distribution during the Middle-Late Triassic.