A paper published this week suggests these dinosaurs shrank for 50 million years as they assumed their new identities as feathered creatures of the sky.
Researchers used a massive fossil database to plot and analyze over 1,500 anatomical traits and reconstruct a vast dino family tree. Their efforts showed theropods shrank in size 12 times over 50 million years leading up to the emergence of birds -- from giant meat-eater to smaller raptor and eventually to regal bird. Along the way, the dinosaurs not only became smaller but also got faster, and developed more pronounced feathers, as well as wishbones and wings.
"Birds evolved through a unique phase of sustained miniaturization in dinosaurs," explained Professor Michael Lee, researcher at both the University of Adelaide's School of Earth and Environmental Sciences and the South Australian Museum.
Lee is the lead author of the study, published in the journal Science.
"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," Lee added. "Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins."
Ultimately, Lee says, theropods out-evolved other lineages of dinosaurs -- learning to climb, glide and forage trees for new food sources.
"This evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins."