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.
U.S. researcher, author, paleontologist, and illustrator
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.
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To a fair extent the Tyrannosaurus species are the tyrannosaur's of tyrannosaurs; they have taken to an extreme the development of skull size, strength, and power. This and the larger, more forward-pointing mid-upper jaw teeth suggest a more potent wounding ability than the albertosaur's. The stoutness of Tyrannosaurus relative to albertosaurs is readily apparent in the skeletal restorations. They are not as graceful, but they have a well-proportioned, majestic attractiveness of their own.
[Velociraptors] are among my very favourite dinosaurs. Their long upcurved skulls, slender yet compact proportions, and great sickle claws make these elegant, attractive, yet demonic animals. There is nothing else like them. Pound for pound, these are among the most powerful of known predators; certainly no other theropod had such a combination of foot, hand, and head weaponry... Among theropods only Tyrannosaurus, with its extreme skull strength, equalled Velociraptor in total power relative to weight.
By the Cretaceous crocodilians of essentially modern form were the theropods [sic] main competitors. Yet crocodilians appear to be less abundant in most Mesozoic deposits than they are later in the mammal-dominated Cenozoic. Not only that, but they tended to be small-bodied: few specimens were as big as American alligators or Nile crocodiles. It is possible that theropods were eating the crocs. Even today, big cats once in a while kill a fairly large crocodilian. A tyrannosaur could have swallowed one whole, and gone into the water after them. Constant attacks could have suppressed croc populations, and favored the smaller, harder to catch species.
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Alas, producers of commercial dinosaur products continue to churn out low quality product that is either obsolete or improperly derivative. Dino documentaries and books have become so plentiful that they are no longer special and I do not try to keep up with them. There are also serious problems with quality and accuracy which often fail to meet the expectations of scientists. More about those problems here. I about kicked in the TV screen when one dino doc claimed that the brain of Tyrannosaurus was as large as that of a gorilla when its IQ was not all that much better than a croc’s. And why are the theropods shown pausing to challenge their prey before they charge, when the actual focus of predators is to hit and overwhelm the victim before it knows what is happening? The low standards are not surprising considering how the media and press frequently carry product that promotes belief in the paranormal. But these are quibbles. Dinosaur science has almost completely transformed over the half century that my neural network has been aware of it. The old stand-bys from Allosaurus to the always strange Stegosaurus are still fascinating, but we now know about armored sauropods, fat-bellied therizinosaurs and multi-winged, near avian, sickle claws. The reptile model is out and the avian-mammalian is dominant.