The Quebrada del Barro Formation is a geological formation of the Marayes-El Carrizal Basin in San Juan Province, Argentina. This formation is the most fossiliferous portion of the Triassic Marayes Group, and is also the youngest unit of the group, overlying the El Carrizal Formation. An unconformity at the top of the Quebrada del Barro Formation separates it from the Cretaceous-age Los Riscos Formation of the El Gigante Group.Gardini et al., 2009, p.554 Part of the formation may be made into a provincial park following the discovery of the fossils of Ingentia, a giant sauropodomorph dinosaur which helped elucidate the early evolution of sauropods.
Sedimentology The Quebrada del Barro Formation formed within a rift basin during a period of renewed fracturing. It encompasses of red sandstones, fine conglomerates, and diamictites. Early hypotheses on the depositional environment proposed that the sediments formed in an alluvial fan or braided river system, while a newer proposal outlines how four different facies within the formation can be used to reconstruct a meandering semiarid floodplain deposited by mudflows and discharging in heterolithic terminal splays.
Fossil content The fauna of Quebrada del Barro is similar to that of the neighboring Los Colorados Formation which is considered to be from the Norian stage of the Late Triassic.Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Triassic, South America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 527–528. . Both formations preserve fossils from groups such as sauropodomorph dinosaurs, cynodonts, and testudinatans. However, Quebrada del Barro is more abundant in sphenodontians (Sphenotitan), tritheledontid cynodonts, and coelophysoid dinosaurs (Lucianovenator), while sauropodomorphs are somewhat less common and aetosaurs are completely absent, in contrast to the Los Colorados Formation. Sphenodontians and cynodonts are also abundant in microfossil assemblages. In addition, the Quebrada del Barro Formation preserves some of the only pterosaur and Dromomeron specimens known from Triassic strata in Argentina. Although the sphenodontian and cynodont-dominated fauna of Quebrada del Barro is akin to that of the Faxinal del Sotorno assemblage of the Brazilian Caturrita Formation, the fauna of the Faxinal del Sotorno assemblage is otherwise indicative of an older part of the Triassic than the Quebrada del Barro Formation.
Dinosaurs Theropods of the Quebrada del Barro Formation Genus Species Material Notes Images LucianovenatorRicardo N. Martínez; Cecilia Apaldetti (2017). "A late Norian-Rhaetian coelophysid neotheropod (Dinosauria, Saurischia) from the Quebrada del Barro Formation, northwestern Argentina". Ameghiniana. in press. doi:10.5710/AMGH.09.04.2017.3065. L. bonoi Several specimens including vertebrae, hip fragments, and a partial tibia A coelophysid theropod
Sauropodomorphs of the Quebrada del Barro Formation Taxon Species Material Notes ImagesIngentiaI. prima"cervical and dorsal vertebrae, scapula"A lessemsaurid sauropod Leyesaurus L. marayensis A massospondylid sauropodomorph. Known from uppermost layers which may belong to a different unit of Hettangian (Early Jurassic) age. Sauropodomorpha sp. Complete foot and tail vertebrae Undiagnostic sauropodomorph remains originally referred to Riojasaurus"Riojasaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 41. .
Other avemetatarsalians Non-dinosaur avemetatarsalias of the Quebrada del Barro Formation Taxon Species Material Notes Images Dromomeron D. gigas A partial femur a lagerpetid Pachagnathus P. benitoi Snout fragment A raeticodactylid pterosaur Pterosauria sp. Partial ulna an indeterminate pterosaur Yelaphomte Y. praderioi Snout fragment A raeticodactylid pterosaur
Pseudosuchians Pseudosuchias of the Quebrada del Barro Formation Taxon Species Material Notes Images "Rauisuchidae" sp. Skull fragments, osteoderms an indeterminate "rauisuchid" smaller than Fasolasuchus Crocodylomorpha sp. A specimen including a partial osteoderm and vertebrae fragments Indeterminate, possibly a "sphenosuchid" Crocodylomorpha sp. Two incomplete specimens including osteoderms, vertebrae, and other bones a protosuchid, possibly synonymous with Hemiprotosuchus
Rhynchocephalians Rhynchocephalians of the Quebrada del Barro Formation Genus Species Material Notes Images Sphenotitan S. leyesi numerous specimens (~50% of all recovered fossils) an eilenodontine sphenodontian
Other reptiles Other reptiles of the Quebrada del Barro Formation Taxon Species Material Notes Images Archosauriformes sp. Maxilla, caudal vertebra, metatarsal, indeterminate limb bone (tibia?) Various indeterminate fragments likely belonging to pseudosuchians or dinosauromorphs Waluchelys W. cavitesta 2 partial skeletons and carapaces an australochelyid stem-turtle
Synapsids Synapsids of the Quebrada del Barro Formation Taxon Species Material Notes Images Tritheledontidae sp. 36 specimens, including a partial skeleton an undescribed tritheledontid cynodont. May be two taxa based on two morphotypes: "long-snout" and "short-snout".
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