Another of Nopcsa's theories that was ahead of its time was that birds evolved from ground-dwelling dinosaurs, which is the theory of cursorial origin of flight. He theorized that the Proavis, a theorized predecessor of birds, was running animal with forearms lifted off the ground, which they would flap as they made a jump. The scales on its forearms would develop into feathers to aid this, and eventually allowing for flight. This theory found favor in the 1960s and later gained wide acceptance, though later fossil finds of tree-living feathered dinosaurs suggest the development of flight may have been more complex than Nopcsa envisioned. Additionally, Nopcsa's conclusion that at least some Mesozoic era reptiles were warm-blooded is now shared by much of the scientific community.