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Rhadinosuchus (proterochampsid from Triassic of Brazil) redescribed

Ben Creisler

A new online paper:

Martín Ezcurra, Julia B. Desojo & Oliver W.M. Rauhut (2015)
Redescription and phylogenetic relationships of the proterochampsid
Rhadinosuchus gracilis (DIAPSIDA: ARCHOSAURIFORMES) from the early
Late Triassic of southern Brazil.
Ameghiniana (advance online publication)

The proterochampsids are small to medium-sized, quadrupedal and
probable semi-aquatic reptiles that were part of the evolutionary
radiation of Archosauromorpha during the Triassic. The group is
restricted to the Middle and Late Triassic of South America with eight
nominal species. Rhadinosuchus gracilis Huene was the first described
proterochampsid and comes from the late Carnian–earliest Norian of
southern Brazil. This genus and species is currently the most
enigmatic and poorly known member of the group and, as a result, we
redescribe here its anatomy and discuss its phylogenetic
relationships. We found that this species can be distinguished from
other proterochampsids and we dismiss the proposed synonym with
Cerritosaurus binsfeldi Price. Our quantitative phylogenetic analysis
found Rhadinosuchus gracilis as more closely related to Gualosuchus
reigi Romer and Chanaresuchus bonapartei Romer than to other
proterochampsids, together forming the subfamily Rhadinosuchinae.
Characters supporting this assignment include a maxilla with a
distinct longitudinal change in slope between lateral and dorsal
surfaces, and dorsal surface of nasal and frontal ornamented by ridges
disposed in a radial pattern. In addition, Rhadinosuchus gracilis was
found as the sister taxon of Chanaresuchus bonapartei based on a
lacrimal with an antorbital fossa that occupies almost half or more of
the anteroposterior length of the ventral process. The topology of the
phylogenetic analysis shows that the Brazilian species do not form a
monophyletic clade and favours multiple dispersal events between the
Ischigualasto-Villa Unión (northwestern Argentina) and the Paraná
(southern Brazil) basins.