Tinguiririca-Fauna
The Tinguiririca fauna summarizes a group of mammals that lived in Patagonia before 33 million to 31.5 million years. Prior to the discovery of many fossils in the Andean regions of South America, the evolution of mammals during this time was unknown until a group of paleontologists in the area of the river Tinguiririca, a 65 km long river in Chile's Región del Libertador General Bernardo O'Higgins, in 1988 to fossil mammal bones came.
Background
30 million years ago South America was a huge island, which had split some 80 million years ago the supercontinent Gondwana from. During this time, the mammals of this continent developed a unique fauna that originated in any other continent. Only 3.5 million years ago to North and South America joined to a continent.
A first major evolution of the mammals of South America was made forty million years ago, when anteaters, created some marsupials and forerunner of sloth. Thirty million years ago, followed by a second development. During the second phase of evolution first occurred on monkeys and rodents in South America that had not evolved on the continent, but had immigrated. Some types of guinea pig relatives as chinchillas reached South America 50 million to 30 million years ago, so millions of years before the continent united with North America. Scientific studies of tooth shapes was discovered that the immigrant animals from Africa and not on an island chain had migrated North to South America. As they crossed the Atlantic, is still unclear. Because of this, however, was not even 1500 km wide at this time, paleontologists suggest that immigration on flotsam was performed using strong east-west flows. Such a trip would have taken about two weeks. In order to survive during the 14 - day journey, the animals may be displaced in a apathetic state during which their metabolic function was reduced.
Although no plants came from the period 33-31 million years ago to the fore, it is assumed that have fed the then living mammals of plants. From earlier times derived fossils that were found in the region of Tierra del Fuego, confirm this hypothesis. In these fossils, the incisors were broad, reduces the canine teeth or even missing - the characteristics of a plant -eater. Many of the mammalian fossils from the area of the river Tinguiririca have greatly increased tooth crowns, which protects against wear and tear of the teeth. The teeth of extant animal groups such as horses and deer are also built so; as they find their food in grasslands, it behaved in the animals of Tinguiririca fauna probably as well. So this area was like in those days probably African savannas. Grasslands developed on other continents until about 18 million years ago. This is probably not only by climate change but by plate movement caused, which provided for the formation of the Andes and ensures even today. By orogeny created valleys where settled the prehistoric mammals. Surrounded by mountains, there was very little precipitation in these basins. Since this condition was unfavorable for the rainforests, there developed grasses that coping better with the changed conditions of life.
The excavations
The first fossil, a fossilized bone was discovered in 1988 in the valley of the Río Tinguiririca by a group of paleontologists who were actually for dinosaur bones. Supposedly, the footprint of a dinosaur had been sighted in the area of the river Tinguiririca. Although these regions had previously been little studied by paleontologists because after former opinion could preserve not living in volcanic rocks, paleontologists hoped to possibly come across dinosaur bones and also to mammalian fossils. The expedition examined the slopes on both sides of the river lay next to dinosaur tracks only fossils of fish and ammonites free. Some of the researchers finally came in about a thousand meters above the river on bone, which seemed to include mammals. In January, a second expedition was sent with seven members, who met in the valley of the Río Tinguiririca to other fossils. Since then, a group of researchers from nearly every other year broke up in this area. As for another expedition in 1994, the road to the Rio Tinguiririca was not passable, paleontologists explored the valleys available to them and there came also on fossils.
Finally, more than 1,500 fossils have been uncovered in mammals, including unknown species of mammals, such as the oldest rodent of South America and four other species, Archaeotypotherium tinguiriricaense, Santiagorothia chilensis, the Urklippschliefer and Eomorphippus that belong to the order of the Notoungulata, ie, to the South American ungulates, and as their oldest representatives apply. Another find was a prehistoric animal bag Klahnia charrieri and bones of a giant sloth. In addition, a skull of the unknown species of ape Chilcebus carrascoensis and a saber-toothed cat was found. The mammals of the Tinguiririca fauna probably died out by a volcanic eruption, for which the volcanic rock, appeals, among which they were buried. During the millions of years always new volcanic eruptions had caused in the Andes that the fossils were buried deeper and deeper under the solidified lava that were 3 m high.