<P> The Mesozoic and Cenozoic deposits have revealed a most interesting vertebrate fauna . This, together with the discovery of the perfect cranium of a chelonian of the genus Myolania, which is almost identical with Myolania oweni of the Pleistocene age in Queensland, forms an evident proof of the connection between the Australian and South American continents . The Patagonian Myolania belongs to the Upper Chalk, having been found associated with remains of Dinosauria . Fossils of the mid-Cretaceous Argentinosaurus, which may be the largest of all dinosaurs, have been found in Patagonia, and a model of the mid-Jurassic Piatnitzkysaurus graces the concourse of the Trelew airport (the skeleton is in the Trelew paleontological museum; the museum's staff has also announced the discovery of a species of dinosaur even bigger than Argentinosaurus). Of more than paleontological interest, the middle Jurassic Los Molles Formation and the still richer late Jurassic (Tithonian) and early Cretaceous (Berriasian) Vaca Muerta formation above it in the Neuquén basin are reported to contain huge hydrocarbon reserves (mostly gas in Los Molles, both gas and oil in Vaca Muerta) partly accessible through hydraulic fracturing . Other specimens of the interesting fauna of Patagonia, belonging to the Middle Cenozoic, are the gigantic wingless birds, exceeding in size any hitherto known, and the singular mammal Pyrotherium, also of very large dimensions . In the Cenozoic marine formation, a considerable number of cetaceans has been discovered . </P> <P> During the Oligocene and Early Miocene large swathes of Patagonia were subject to a marine transgression . The transgression might have temporarily linked the Pacific and Atlantic oceans, as inferred from the findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation . Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography . The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene forming the Chile Triple Junction . At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction was located near the Strait of Magellan . As the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time . The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of ca . 1 km that reversed the Miocene transgression . </P> <P> At a state level, Patagonia lies inside two countries: 10% in Chile and 90% in Argentina . Both countries have organised their Patagonian territories into non-equivalent administrative subdivisions: Provinces and departments in Argentina; and regions, provinces and communes in Chile . Chile being a unitary state, its first - level administrative divisions--the regions--enjoy far less autonomy than Argentine provinces . Argentine provinces have elected governors and parliaments, while Chilean regions have government - appointed intendants . </P> <P> The Patagonian Provinces of Argentina are Neuquén, Río Negro, Chubut, Santa Cruz, and Tierra del Fuego . The southernmost part of Buenos Aires Province can also be considered part of Patagonia . </P>

Desert along the west coast of south america