Researchers from the University of Texas, Stony Brook University, and the American Museum of Natural History presented new evidence in the July 31, 2013, issue of the journal Nature that indicates some terrestrial dinosaurs had developed the brain adaptations that make flight possible before any dinosaur or bird ever took flight.
Modern birds have brains that have a distinctively enlarged forebrain that is adapted to provide superior vision and coordination during flight.
The researchers used X-ray computed tomographic (CT) scans to examine and compare the skulls of the oldest known bird (Archaeopteryx), modern birds, and terrestrial dinosaurs including tyrannosaurs, oviraptorosaurs, and troodontids.
The fossil remains do not contain fossilized brain matter, but a very accurate approximation of the size of the brain and the placement of the various functional parts of the brain can be determined from the size and shape of the interior of the skull.
The researchers found that oviraptorosaurs and troodontids had brains similar in size, shape, and function to the brain of Archaeopteryx and modern birds despite being totally terrestrial dinosaurs. Some of the terrestrial dinosaurs had larger brains than Archaeopteryx. Some terrestrial dinosaur brains that had a higher degree of relationship to modern birds than flying dinosaurs.
The conclusion is that the brain that allows birds to fly developed in terrestrial dinosaurs long before any dinosaur took to the air for the first time.