CONICET | Buscador de Institutos y Recursos Humanos

The proterochampsids are a Triassic group which belongs to the Archosauriformes. The fossil record of the clade is restricted to the late Middle to the early Late Triassic of South America. The phylogenetic relationships of this group have not been analyzed at specific level and including all the taxa from South America yet. The aim of the present contribution is to establish a phylogenetic hypothesis of proterochampsid interrelationships at specific level and test the monophyly of the clade a whole. The employed data matrix was a modified version to that published by Dilkes and Sues (2009). It includes four new characters and five taxa of proterochampsids at species level (Proterochampsa barrionuevoi, Proterochampsa nodosa, Chanaresuchus bonapartei, Gualosuchus reigi and Chanaresuchus sp nov.). Also add the Brazilian specie Cerritosaurus binsfeldi which has been considered within the Proterochampsidae by some authors and within Cerritosauridae by others. But Rhadinosuchus garcilis is excluded because this specie is actually in study by other researchers. The matrix consists of 24 taxa, including basal archosaurs (e.g. Saurosuchus, Arizonasaurus), archosauriforms (e.g. Doswellia, Vancleavea), and the arcosauromorph Prolacerta and Mesosuchus, which was the root taxa. The data set is composed of 89 characters: 34 from the skull, 14 from the braincase, and 41 from postcranium. The recovered most parsimonious trees found a new clade named Proterochampsoidea. These clade is formed by a trichotomy that includes Vancleavea campi, Tropidosuchus romeri, and the innominated group A. The group A is composed of Doswellia kaltenbachi and Proterochampsidae. In the present contribution the conformation of Proterochampisdae follows that proposed by Barberena (1982), including the genera Chanaresuchus Romer, 1971, Proterochampsa Reig, 1959, and Gualosuchus Romer, 1971. This group is supported by two synapomorphies: basiesphenoid with a semilunar groove and pterygoid with only one row of teeth on its transverse flange. Besides, the monophyly of the genus Proterochampsa is supported by the presence of a skull ornamented by nodular crests. The clade composed by the two species of Chanaresuchus is supported by the presence of a skull ornamented by longitudinal crests and depressions on the nasals and parietal and with a radial pattern on the frontals. Finally, Chanaresuchus is nested as the sister-group of Gualosuchus, based on the presence of a depressed region on the maxilla-lacrimal contact. Finally, this analysis support the monophyly of Proterochampsidae composed by Proterochampsa, Chanaresuchus and Gualosuchus reigi, but excluding Tropidosuchus romeri.

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