Proterochampsia: an endemic archosauriform clade from South America

Abstract

Proterochampsia is a monophyletic group of crocodile-like archosauriforms currently endemic to the late Middle and early Late Triassic of South America considered as one of the potential successive sister-taxa of the crown group Archosauria. The proterochampsians come from the Ischigualasto-Villa Unión Basin in the west of Argentina and the Parana Basin in the south of Brazil. The traditional composition of the group includes the genera Cerritosaurus Price 1946, Proterochampsa Reig 1959 (with two species: P. barrionuevoi in Argentina and P. nodosa Barberena 1982 in Brazil), Chanaresuchus Romer (with two species from Argentina: C. bonapartei Romer and C. ischigualastensis Trotteyn et al. 2012), Gualosuchus reigi Romer 1971 and Tropidosuchus romeri Arcucci 1990. After a precladistic history of confusion about their relationships with crocodilians, in the last 20 years new discoveries of taxa, and more systematic and phylogenetic studies, have clarified their position as non-archosaurian archosauriforms and their relationships with other Triassic archosaurs.

The Origin and Early Evolution of Sauria: Reassessing the Permian Saurian Fossil Record and the Timing of the Crocodile-Lizard Divergence

“…Vertebrae 2 (A, E, I, M, Q, U), 3 (C, G, K, O, S, W), 4 (B, F, J, N, R, V) and 5 (D, H, L, P, T, X) sensu Parrington [8]. Scale bar equals 1 cm.…”

Redescription and Phylogenetic Relationships of the Proterochampsid Rhadinosuchus gracilis (Diapsida: Archosauriformes) from the Early Late Triassic of Southern Brazil

“…PROTEROCHAMPSIDS are a group of small to medium-sized quadruped and semi-aquatic (at least Proterochampsa Reig, 1959) archosauriforms with an overall crocodile-like aspect (Trotteyn et al, 2013). Proterochampsids were part of the evolutionary radiation of Archosauromorpha during the Triassic and they have been regarded as close relatives (Benton and Clark, 1988;Dilkes and Sues, 2009;Ezcurra et al, 2010;Nesbitt, 2011;Dilkes and Arucci, 2012) or the immediate sister-taxon of crownarchosaurs (Gauthier, 1984;Sereno and Arcucci, 1990;Sereno, 1991;Parrish, 1993;Juul, 1994).…”

“…Proterochampsids differ from most other archosauromorphs in the presence of dorsally facing external nares, strongly ornamented skull roofs, very long snouts (ca. 50-55% of total skull length; e.g., Chanaresuchus bonapartei Romer, 1971: MCZ 4037, 4039) and-particularly in some species-a strongly dorsoventrally compressed skull with dorsally facing antorbital fenestrae and orbits (Trotteyn et al, 2013). The fossil record of the group is currently restricted to eight nominal species from the Middle and Late Triassic Ischigualasto-Villa Unión and Paraná basins of northwestern Argentina and southern Brazil, respectively (Reig, 1959;Romer, 1971;Kischlat, 2000;Dilkes and Arcucci, 2012;Trotteyn et al, 2013).…”

“…50-55% of total skull length; e.g., Chanaresuchus bonapartei Romer, 1971: MCZ 4037, 4039) and-particularly in some species-a strongly dorsoventrally compressed skull with dorsally facing antorbital fenestrae and orbits (Trotteyn et al, 2013). The fossil record of the group is currently restricted to eight nominal species from the Middle and Late Triassic Ischigualasto-Villa Unión and Paraná basins of northwestern Argentina and southern Brazil, respectively (Reig, 1959;Romer, 1971;Kischlat, 2000;Dilkes and Arcucci, 2012;Trotteyn et al, 2013). Several papers have improved our anatomical and phylogenetic knowledge of proterochampsids in the last few years (e.g., Trotteyn, 2011;Trotteyn andHaro, 2011, 2012;Dilkes and Arcucci, 2012;Trotteyn et al, , 2013Raugust et al, 2013;Trotteyn and Ezcurra, 2014), but there are still some poorly known species that constitute a gap in the knowledge of the group.…”

“…As a result, several aspects of the anatomy and the phylogenetic relationships of the species remain uncertain (Desojo et al, 2010;Trotteyn et al, 2013).…”