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The birds originated from small bipedal, ground-living archosaurs, which evolved the anatomical, physiological, and behavioural preconditions for flying as an adaptation to climb and descend from tree-trunks. The habit of flapping the forelimbs, which initiated the ability to fly, originated before the wings had arisen. FOREWORD. In 1860 was in Solnhofen in the southern Germany discovered the most significant fossil of the vertebrate evolution. It was Archaeopteryx, dated to Upper Jurassic and thus about 150 million years old. It has until now been discovered 7 specimens of this fossil. Archaeopteryx was unmistakably a winged and feathered, two legged creature, and as its similarity to two-legged dinosaurs is apparent it is obvious that birds and dinosaurs are closely related. No doubt was Archaeopteryx able to fly, of which its well-developed wings were evidence. And as feathers and wings must have taken a very long time to evolve, and as Archaeopteryx is likely not to have been the only one of its kind, it can safely be concluded that at that time existed feathered, flying bird-like vertebrates, closely related to dinosaurs. In the following years were nevertheless a great number of theories*) forwarded on the evolutionary origin of birds and on the relation of birds to dinosaurs, and for the time being is a popular theory that birds are dinosaurs and originate from two legged ones which ran on the ground and evolved wings and then began to fly. According to this theory feathers are not a unique bird trait, and it is claimed that the dinosaurs in general were feathered. The only support for this bizarre statement is that some dinosaur-like fossils of China, discovered in the 1990-th, had feathers. **) A weakness – to put it gently – of that theory is that the Chinese fossils are from Cretaceous, more than 25 million years younger than Archaeopteryx, and were most probably ancestors of archaeopteryx-relatives from Jurassic or earlier, which have ceased to fly and reduced their wings and plumage just as ostriches, emus, kiwis and other modern ratites later on have done. They provide no evidence what so ever about the bird/dinosaur relation and nothing can be concluded from them about the dinosaurs being feathered. Another weakness of the idea of the dinosaurs as feathered is that no fossils of dinosaurs have ever been discovered with even traces of feathers. The assertion that the dinosaurs generally were feathered is with no foundation whatsoever. Until furthered evidence feathers must be considered as an exclusive bird-quality not to be found in any other group of vertebrates. Another point is how to explain how two legged; dinosaur-like bird-ancestors which lived on the ground could possibly have evolved wings and the ability to fly. In 1989 I published a theory in Danish “Fuglene – sådan opstod de!” and in 1997 in English “The Origin of Flapping Flight in Birds.” The latter is in full to be found at the Internet.