[F] Ischigualasto Formation - Argentina
Badland exposures of the Ischigualasto Formation crop out in the Isschigualasto-Ville Union Basin of northwestern Argentina. This basin is on of several small rift basins that formed along the western margin of South America before the breakup of Pangaea.
The Ischigualsto Formation is included whitin the [Agua de la Pena Group], which is a thick succession of continental Triassic strata that accumulated during the Middle and Late Triassic. Beds of the Ischigualsto Formation rest upon sediments of the [Los Rastros Formation] and pass up into the red and orange cliffs of the Los Colorados Formation.
Deposits of the Ischigualsto Formation located in northwestern Argentina, near the border with Chile consist of medium- to coarse-grained conglomeratic sandstones, siltstones and silty mudstones. Several thin volcanic ash horizons are internedded whitin the Ischigualsto section. Radioisotopic dating of one of these beds indicates that deposition of the Ischigualsto Formation began approximately 228 million yars ago (Rogers et al., 1993). This places the formation and its vertebrate fossils firmly whitin the Carnian Stage.
Based on the analysis of Ischigualasto sediments we can conclude that early dinosaurs inhabited fluvial and floodplain settings. It is the only place in the world where nearly all of the Triassic is represented in an undisturbed sequence of rock deposits, and both the overlying and underlying formations have also yielded important fossils of early dinosaurs as well as of early synapsids and freshwater fish.
The Harvard paleontologist A. S. Romer was so impressed by this formation that he wrote the following: \\\"It is the delight of all vertebrate paleontologists, to get up in the morning, leave the tent and find themselves surrounded by the most extraordinary fossil cemetery ever imagined. And all perfectly preserved. --A. S. Romer , 1958\\\"An arid badland in northwestern Argentina, is such a bizarre and rugged terrain that it has given the popular name \\\"Valley of the Moon\\\".
In the Carnian, 230 million years ago, this area was a volcanically active floodplain dominated by rivers and had a strongly seasonal rainfall. Only about 6% of all tetrapods found there are dinosaurs. Dinosaur fossils from this site include both early ornithischians, and putative early saurischians. And therefore establish not only that dinosaurs existed by this time, but that they had begun to diversify.
Eodromaeus murphi - Valle de la Luna Member, Ischigualsto-Villa Union Basin - Saurischia Theropoda - Triassic Late Carnian
Eoraptor lunensis - Valle de la Luna Member, Ischigualsto-Villa Union Basin - Saurischia Theropoda - Triassic Late Carnian
Frenguellisaurus ischigualastensis - Provincia de San Juan - Theropoda Incertae Sedis \\\"Carnosaurs\\\" - Triassic Late Carnian
Herrerasaurus ischigualastensis - Provincia de San Juan - Herrerasauria Herrerasauridae - Triassic Late Carnian
Ischisaurus cattoi - Provincia de San Juan - Herrerasauria Herrerasauridae - Triassic Late Carnian
Panphagia protos - Saurischia Sauropodomorpha - Triassic Late Carnian
Pisanosaurus mertii - Provincia de La Rioja - Ornithischia Sedis Mutabilis - Triassic Late Carnian
Sanjuansaurus gordilloi - Provincia de San Juan - Herrerasauria Herrerasauridae - Triassic Late Carnian
Staurikosaurus sp. (2) - Provincia de San Juan - Theropoda Staurikosauridae - Triassic Late Carnian