Lagerpeton chanarensis (Romer 1971; Novas and Agnolin 2016) Middle Triassic, ~ 240 mya, ~70cm long; originally MLP 64-XI-14-10, later PULR 06, additional material PVL 4619, PVL 4625) was originally considered a dinosauromorph, like Marasuchus. Here convergent evolution has created a bipedal chanaresuchid, derived from Tropidosuchus that has similar pedal proportions to the second specimen attributed to Tropidosuchus. Only the hindlimb and a portion of the lumbar and caudal regions of the vertebral series have been attributed to Lagerpeton.

Gualosuchus reigi (Romer 1970) was the largest Chañares formation taxon. The orbits were more lateral and taller. The arch between the temporal fenestra were parallel. In the large reptile tree, skull only Gualosuchus nests with skull-less Lagerpeton.

Recently a femur attributed to Dromomeron was described by Irmis et al. (2007) and Nesbitt et al. (2009) as a sister to Lagerpeton. This may be be true. However, neither nested as dinosaur ancestors in the large study. Prior nestings are errors resulting from too small of an inclusion set. In those studies, pterosaurs and these bipeds were derived from parasuchians, like Parasuchus, which are almost polar opposites in terms of morphology. Here a more gradual demonstration of the evolution of each taxa is provided.

Arcucci A 1986 New materials and reinterpretation of Lagerpeton chanarensis Romer (Thecodontia, Lagerpetonidae nov.) from the Middle Triassic of La Rioja, Argentina. Ameghiniana 23(3-4):233-242. online pdf

Bonaparte JF 1994. Dinosaurios de America del Sur. Impreso en Artes Gráficas Sagitario. Buenes Aires. 174pp. ISBN: 9504368581

Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.

Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218.

Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios”. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.

Romer AS 1971. The Chañares (Argentina) Triassic reptile fauna. XI. Two new long-snouted thecodonts, Chanaresuchus and Gualosuchus. Breviora 379: 1–22.

Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton
wiki/Gualosuchus