New vertebrate findings shed light on the controversial age of the Quebrada del Barro Formation (Marayes – El Carrizal Basin).

MARTÍNEZ, R.N.; APALDETTI C.; PRADERIO A.; FERNÁNDEZ, E.; C. COLOMBI,; ALCOBER O.; SANTI MALNIS; CORREA, G.A.; ABELÍN D.

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Simposio; V Simposio Argentino del Jurásico y sus límites; 2013

Marayes-El Carrizal is an extensional continental basin (Northwestern Argentina) developed during the Early Mesozoic at the southwestern margin of Pangea. Quebrada del Barro Formation is the uppermost unit of the sequence in where vertebrate fossils have been found. The controversial age of the Quebrada del Barro Formation has been regarded such as Cretaceous, Rhaetian and Norian sensu different authors. Based on the recent find of the dinosaur Leyesaurus marayensis Apaldetti et al—a basal sauropodomorph closely related to the South African genus Massospondylus—was suggested a Lower Jurassic age to the Quebrada del Barro Formation. Here we report the discovery of a new faunal association from the upper layers of the Quebrada del Barro Formation that includes eucynodonts, pseudosuchids, basal sauropodomorphs, and sphenodontids. Preliminary comparative analyses indicate that some of the new findings have high affinities with the coloradians Chaliminia Bonaparte (Cynodontia: Tritheledontia), Pseudhesperosuchus Bonaparte (Pseudosuchia: Sphenosuchia), and Riojasaurus Bonaparte (Dinosauria: Sauropodomorpha), which suggest a like-Triassic assemblage for these layers. On the other hand, a geologic survey conducted by the authors indicates that all the finds of the massospondylid Leyesaurus, used to suggest a Lower Jurassic age to the Quebrada del Barro Formation, are located in a different and overlaying stratigraphic unit. The new faunal association, which includes at least three equivalent components of the Los Colorados Formation, supports the Norian age of the Quebrada del Barro Formation whereas the overlaying unit includes only basal sauropodomorphs typical from Lower Jurassic units.