When it was assumed that birds did not evolve from dinosaurs, it was correspondingly presumed that their flight evolved among climbers that first gli… - Gregory S. Paul

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When it was assumed that birds did not evolve from dinosaurs, it was correspondingly presumed that their flight evolved among climbers that first glided and then developed powered flight. This has the advantage that we know that arboreal animals can evolve powered flight with the aid of gravity, as per bats. When it was realized that birds descended from deinonychosaurs, many researchers switched to the hypothesis that running dinosaurs learned to fly from the ground up. This has the disadvantage that it is not certain whether it is practical for tetrapod flight to evolve among ground runners working against gravity.
The characteristics of birds indicate that they evolved from dinosaurs that had first evolved as bipedal runners, and then evolved into long armed climbers. If the ancestors of birds had been entirely arboreal, then they should be semiquadrupedal forms whose sprawling legs were integrated into the main airfoil, like bats. That birds are bipeds whose erect legs are separate from the wings indicates that their ancestors evolved to run.

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About Gregory S. Paul

Gregory S. Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal.

Also Known As

Native Name: Gregory Scott Paul

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The dinosaur world I grew up in was classical. They were universally seen as scaley herps that inhabited the immobile continents. There was no hint that birds were their direct descendents. Being reptiles, dinosaurs were cold-blooded and rather sluggish except perhaps for the smaller more bird-like examples. They all dragged their tails. Forelimbs were often sprawling. Leg muscles were slender in the reptilian manner. Intellectual capacity was minimal, as were social activity and parenting; the Knight painting of a Triceratops pair watching over a baby threatened by the Tyrant King was a notable exception. Hadrosaurs and especially sauropods were dinosaurian hippos, the latter perhaps too titanic to even emerge on land, and if they did so were limited by their bulk to lifting one foot of the ground at a time. Suitable only for the lush, warm and sunny tropical climate that enveloped the world from pole to pole before the Cenozoic, a cooling climate and new mountain chains did the obsolete archosaurs in, leaving only the crocodilians. Dinosaurs and the bat-winged pterosaurs were merely an evolutionary interlude, a period of geo-biological stasis before things got really interesting with the rise of the energetic and quick witted birds and especially mammals, leading with inexorable progress to the apex of natural selection: Man. It was pretty much all wrong. Deep down I sensed something was not quite right. Illustrating dinosaurs I found them to be much more reminiscent of birds and mammals than of the reptiles they were supposed to be. I was primed for a new view.

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Tyrannosaurus rex did not have 6-to-8-inch serrated teeth and an arc of D-cross-sectioned teeth set in a massive, powerful skull just to consume rotting carcasses! These were killing tools. In sharp contrast are the weak beaks and feet of vultures and condors- the only true living scavengers.

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