domingo, 16 de março de 2014

Viveu nos Pampas a maior ave voadora que já existiu sobre a Terra!

3,5 metros com envergadura: 5,8 a 8m e altura entre 1,7 a 2 metros. Pesava entre 60 a 110 kg

Argentavis magnificens foi uma ave de rapina extinta da família Teratornithidae que viveu na América do Sul no Mioceno.

Nomeada como a maior ave que já voou, tinha grande dificuldade de alçar vôo devido sua musculatura incompatível com seu tamanho e provavelmente decolava correndo em declive. Com grande desempenho de planeio, ela aproveitava termais e ventos ascendentes comuns nos Andes para se manter no ar. Estima-se que dessa maneira a espécie podia percorrer até 300 km por dia.


O texto abaixo foi compilado do livro HBW, Volume 12, pp 26:

Raptorial birds have evolved several times throughout the fossil record, both within the toothed birds (e.g. Boluochia of the Enantiornithes) and within modern birds. The most obvious of these latter groups are the so-called 'raptors', currently within the order Falconiformes. However, this grouping is artificial, forcing together two groups of birds of very different origins. That of the Accipitridae and their relatives is still ambiguous. In the case of the Cathartidae, both molecular and morphological work point to an ancestry shared with the storks (Ciconiidae), rather than fa1coniform raptors. The oldest fossil in the group, that of the small Diatropornis ellioti, comes not from the Americas, but from the Quercy Fissure deposits of France, and is Late Eocene to Early Oligocene in age (Cracraft & Vickers-Rich 1972, Mourer-Chauvin 2002). Two other species come from early in the history of the Cathartidae: one, Phasmagyps patritus, originates from the Early Oligocene of Colorado, and therefore comes from within the range of modern species. The other, Oligocathartes olsoni, is from the Lower Oligocene of England. However, Mayr (2005a) regards the latter as too fragmentary to be identifiable and perhaps this species should be removed from the Cathartidae. Although the origins of the family may not have been in the New World, or, at least, their origins may have been shared with Europe (as seems to be the case with many groups), the majority of species are from the Americas. Hadrogyps aigialeus represents a small stocky 'condor' from the Middle Miocene of California and was probably a coastal species (Emslie 1988), while the next 'large condor' is the Late Miocene/Early Pliocene Perugyps diazi, from the Pisco formation of Peru. Together, this suggests that condors evolved in North America and spread to South America by the Late Miocene (Stucchi & Emslie 2005). Cathartid vultures were at their most diverse in the Pleistocene, when several species of condor existed in North America. The formerly widespread Gymnogyps cafifornianus, which we call the 'California Condor', had a range that stretched throughout the USA in the Late Pleistocene, but its range contracted with the progressive extinction of the North American megafauna (Steadman & Miller 1987). Another species, G. kofordi, was described from the Early Pleistocene of Florida, while a larger form of the modern species, G. cafifornianus amplus, was exumed from the La Brea tar pits, California. In addition, a closely related condor, G. varonai, was found in Late Pleistocene deposits of Cuba. Alongside the Cathartidae in the Americas was another vulture-like group, the teratorns (Teratornithidae). Three of the four species were North American, the exception being Argentavis magnificens, whose fossil was discovered in Late Miocene deposits of Argentina, and which must have been a huge bird, with a wingspan of 6-8 m. Indeed, A. magnificens is considered to be the largest flying bird ever to have lived. Not only was this the largest of the teratorns, but it was also the oldest (Campbell & Tonni 1983), although it was not the first species in the family to be described. That honour goes to Teratornis merriami, which was also the most abundant of the group. Teratornis was a species whose temporal range extended from the Pliocene until the Late Pleistocene. It is probably typical of the group in many ways. Merriam's Teratorn, as it has been named, was also a large bird, but only half the size of Argentavis, having a wingspan of a mere 3-4 m; if one compares this with the Andean Condor (Vultur gryphus), which can attain a span of about 3·2 m, one can begin to see the true size of these birds. Traditionally, the teratorns have been portrayed as giant versions of the Cathartidae, even sharing their scavenging habits, a perception reinforced by the shape of the skull and by discovery of over a hundred individals of T. merriami in the asphalt deposits of La Brea, a site that has produced hundreds of fossils of raptors and vultures, all thought to be attracted to the animals that became trapped there. However, instead of being scavengers, teratorns are now considered to have been active hunters, with T. merriami being a fish-eater and facultative scavenger (Hertel 1995). In the air, these birds may have soared like condors, but on the ground they were apparently more agile: in the smaller teratorns such as T. merriami, this agility may have helped them in their attempts to take off. How the giant A. magnificens took off is a matter for conjecture, but the age of the deposits in which it was found and the geographical position of the site indicate that its flight was enabled by the constant strong winds that crossed the South American plains in the Late Miocene, unhindered by the Andes, which were, at the time, undergoing upheaval. Another deduction from the age of this specimen is that teratorns probably evolved in South America, later spreading north into North America, before finally dying out at the end of the Pleistocene.

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