Fuglenes oprindelse: Forskelle mellem versioner
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*[[Gerhard Heilmann]] |
*[[Gerhard Heilmann]] |
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==Eksterne henvisninger== |
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*[http://www.dr.dk/Videnskab/viden_om/Programmer/Dino/Fuglenes_forfader.htm Viden Om: Fuglenes Forfader] |
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[[Kategori:Flyvende_dyr]] |
[[Kategori:Flyvende_dyr]] |
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Versionen fra 13. jun. 2009, 10:02
Fuglenes oprindelse kan undersøges takket være en række fundne uddøde fugleslægter, der stadigvæk bar mange skeletkendetegn.
En del tyder på at fugle stammer fra en bestemte gruppe dinosaurer, og er meget nært beslægtet med familien Dromaeosauridae. Fossile rester af Dromaeosaurer og primitive fugle har mange lighedstræk, og derfor bør alle fugle kaldes for 'flyvende dinosaurer'. Fugle stammer altså ikke fra flyveøgler [1] , som ikke engang var dinosaurer, omend nært beslægtede til dinosaurer.
Der er i de senere år (siden 1990'erne) blevet fundet en del fjerede dinosaurer, måske et klart bevis for en forbindelse mellem dinosaurer og fugle. [2] [3] De fleste af disse fund er fra Kina, hvor fundsteder med de nødvendige omstændigheder til bevaring af fjer- og hudaftryk findes. Andre former synes at have en nopret hud med hårlignende strukturer.
Foreløbig er der fundet fjer/dun hos sinosauropteryx, protarchaeopteryx, caudipteryx og confuciusornis, alle fra det nordlige Kinas Yixian formation. Familien dromaeosauridae synes at have været forsynet med egentlige fjer, ikke blot dun, og anses af de fleste forskere som nært beslægtet med fuglene. Det er ikke usandsynligt at dromaeosaurer har kunnet flyve.
Samtidig finder man flere og flere af fuglenes særlige skeletale kendetegn hos små theropoder. Kendetegn, som man troede var tilpasninger til flyvning dukker op hos former, der netop ikke er fugle. [4] [3] [5] [6] Udviklingen af flyvning hos fuglene eller deres dinosaurforfædre er således mere kompliceret end som så. [7] [8] [9] [10] [11]
Senest er der dog igen dukket tvivl op om fugle stammer fra dinosaurer, da man har fundet fugle fra før dinosaurernes tid. [12]
Liste over primitive fugle:
Kilder/referencer
- ^ dinodatabase.com: Flying Dinosaurs Citat: "...pterosaurs...were not dinosaurs, although they were related to them; they were flying reptiles..."
- ^ BBCNews, 6 March, 2002, 'Modern' feathers found on Chinese dino
- ^ a b dinohunters.com: Microraptor Citat: "...Microraptor zhaoianus...The discovery of a 130-million-year-old fossil of a feathered dinosaur provides dramatic evidence that birds evolved from the ancient reptiles, according to new research...Theropod dinosaurs and birds share about 100 anatomical features, including a wishbone, swiveling wrists and three forward-pointing toes. Norell said dromaeosaurs were theropod dinosaurs thought to be most closely related to birds..."
- ^ 13 October 2005 BBC News: Bird-like dinosaur forces rethink Citat: "...A rooster-sized dinosaur with a long, slender snout and wing-like limbs is forcing a rethink on bird evolution...The authors say the discovery Rahonavis and Buitreraptor have long and wing-like forelimbs could imply that flight evolved twice, once in birds and once among this group of Gondwanan dromaeosaurs..."
- ^ 2005-10-18, Sciencedaily: Wright Brothers Upstaged! Dinos Invented Biplanes Citat: "..."It seems likely that Microraptor invented the biplane 125 million years before the Wright 1903 Flyer."..."
- ^ University of California, Berkeley, The Dinosauria: Truth is Stranger than Fiction Citat: "...Dinosaurs are not extinct. Technically. Based on features of the skeleton, most people studying dinosaurs consider birds to be dinosaurs..."
- ^ University of California, Berkeley: Are Birds Really Dinosaurs? Citat: "...In fact, the evidence is overwhelmingly in favor of birds being the descendants of a maniraptoran dinosaur...Some researchers today do not agree that dinosaurs gave rise to birds, and are working to falsify this theory, but so far the evidence for the theory has swamped their efforts...."
- ^ birding.com: Are Birds Dinosaurs? Citat: "...YES they are...NO they are not..."
- ^ Tree of Live web project: Neornithes, Modern Birds Quote: "...Introduction...Whether modern birds are most closely related to dinosaurs or crocodylian ancestors is a point of current debate...."
- ^ 20 January, 2005, BBC News: Cretaceous duck ruffles feathers Citat: "...Fossil remains of a bird that lived 70 million years ago appear to belong to a relative of modern ducks and geese..."This is basically an unidentifiable bundle of bones," Alan Feduccia, a bird expert from the University of North Carolina, US, said...And now all of a sudden it's a modern duck..."
- ^ 11 July 2006, Big dinosaurs 'had warmer blood' Citat: "...The bigger a dinosaur was, the warmer its blood...smallest dinosaurs had temperatures of around 25C, close to environmental temperatures...biggest dinosaurs - had a body temperature of just over 40C...Most animals cannot tolerate body temperatures of above 45C, so Apatosaurus is both near the upper limit..."
- ^ Oregon State University (2009, June 9). Discovery Raises New Doubts About Dinosaur-bird Links. ScienceDaily. Retrieved June 13, 2009 Citat: "..."This discovery probably means that birds evolved on a parallel path alongside dinosaurs, starting that process before most dinosaur species even existed."...Warm-blooded birds need about 20 times more oxygen than cold-blooded reptiles, and have evolved a unique lung structure that allows for a high rate of gas exchange and high activity level. Their unusual thigh complex is what helps support the lung and prevent its collapse...The implication, the researchers said, is that birds almost certainly did not descend from theropod dinosaurs, such as tyrannosaurus or allosaurus..."For one thing, birds are found earlier in the fossil record than the dinosaurs they are supposed to have descended from," Ruben said. "That's a pretty serious problem, and there are other inconsistencies with the bird-from-dinosaur theories..."