Massive meat-eating ground-dwelling dinosaurs shrunk over 50 million years and evolved into agile flying birds, according to new research. Scientists from the University of Southampton have presented in the journal Science a detailed family tree of dinosaurs and their bird descendants, which maps out the evolutionary transformation.
They showed that the branch of theropod dinosaurs, which gave rise to modern birds, were the only dinosaurs that kept getting inexorably smaller. Darren Naish, vertebrate palaeontologist, said: "These bird ancestors also evolved new adaptations, such as feathers, wishbones and wings, four times faster than other dinosaurs."
Associate professor Michael Lee, from the University of Adelaide, added: "Birds evolved through a unique phase of sustained miniaturisation in dinosaurs. Being smaller and lighter in the land of giants, with rapidly evolving anatomical adaptations, provided these bird ancestors with new ecological opportunities, such as the ability to climb trees, glide and fly. Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins."
Co-author Gareth Dyke, senior lecturer in vertebrate palaeontology at the University of Southampton, said: "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 examined more than 1,500 anatomical traits of dinosaurs to reconstruct their family tree. The researchers used sophisticated mathematical modelling to trace evolving adaptions and changing body size over time and across dinosaur branches.
The international team also included Andrea Cau, from the University of Bologna and Museo Geologico Giovanni Capellini. The study concluded that the branch of dinosaurs leading to birds was more evolutionary innovative than other dinosaur lineages. Associate Prof Lee added: "Birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less evolvable relatives could not."