Did the sinosauropteryx fly?
Sinosauropteryx
Despite its feathers, most palaeontologists do not consider "Sinosauropteryx" to be a bird. Phylogenetically, the genus is only distantly related to the clade Aves, usually defined as "Archaeopteryx lithographica" plus modern birds. The scientists who described "Sinosauropteryx", however, used a character-based, or apomorphic, definition of the Class Aves, in which any animal with feathers is considered to be a bird. They argued that the filamentous plumes of "Sinosauropteryx" represent true feathers with a rachis and barbs, and thus that "Sinosauropteryx" should be considered a true bird. They classified the genus as belonging to a new biological order, Sinosauropterygiformes, family Sinosauropterygidae, within the subclass Sauriurae. These proposals have not been accepted, and "Sinosauropteryx" is generally classified in the family Compsognathidae, a group of small-bodied long-tailed coelurosaurian theropods known from the Late Jurassic and Early Cretaceous of Asia, Europe, and South America.
Quetzalcoatlus
The nature of flight in "Quetzalcoatlus" and other giant azhdarchids was poorly understood until serious biomechanical studies were conducted in the 21st century. One early (1984) experiment by Paul MacCready used practical aerodynamics to test the flight of "Quetzalcoatlus". MacCready constructed a model flying machine or ornithopter with a simple computer functioning as an autopilot. The model successfully flew with a combination of soaring and wing flapping; the model was based on a then-current weight estimate of around , far lower than more modern estimates of over . The method of flight in these pterosaurs depends largely on weight, which has been controversial, and widely differing masses have been favored by different scientists. Some researchers have suggested that these animals employed slow, soaring flight, while others have concluded that their flight was fast and dynamic. In 2010, Donald Henderson argued that the mass of "Q. northropi" had been underestimated, even the highest estimates, and that it was too massive to have achieved powered flight. He estimated it in his 2010 paper as . Henderson argued that it may have been flightless.