"These bird ancestors also evolved new adaptations, such as feathers, wishbones and wings, four times faster than other dinosaurs," says co-author Darren Naish, Vertebrate Palaeontologist at the University of Southampton.
"Birds evolved through a unique phase of sustained miniaturisation in dinosaurs," says lead author Associate Professor Michael Lee, from the University of Adelaide's School of Earth and Environmental Sciences and the South Australian Museum.
Co-author Gareth Dyke, Senior Lecturer in Vertebrate Palaeontology at the University of Southampton, adds: "The dinosaurs most closely related to birds are all small, and many of them - such as the aptly named Microraptor - had some ability to climb and glide."
The study concluded that the branch of dinosaurs leading to birds was more evolutionary innovative than other dinosaur lineages. "Birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less evolvable relatives could not," says Associate Professor Lee.
The study is published in the Journal Science.