VIDEO: This is How Large, Meat-Eating Dinosaurs Became Feather-Weight Flyers

Meet the ancestors: The feathered dinosaur Microraptor pounces on a nest of primitive birds (Sinornis). Both species lived during the Cretaceous Period (~120 million years ago) in what is now northern China. Image: Brian Choo.

A study led by an Adelaide scientist has revealed how massive, meat-eating, ground-dwelling dinosaurs evolved into agile flying birds — they just kept shrinking and shrinking, for more 50 million years.

In the journal Science, the researchers present a detailed family tree of dinosaurs and their bird descendants which maps out this unlikely transformation.

They showed that the branch of theropod dinosaurs, which gave rise to modern birds, were the only dinosaurs which kept getting smaller.

The bird ancestors also evolved new adaptations, such as feathers, wishbones and wings, four times faster than other dinosaurs

“Birds evolved through a unique phase of sustained miniaturisation in dinosaurs,” says lead author Michael Lee, from the University of Adelaide’s School of Earth and Environmental Sciences and the South Australian Museum.

“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.”

The study examined more than 1,500 anatomical traits of dinosaurs to reconstruct a family tree. The researchers used sophisticated mathematical modelling to trace evolving adaptions and changing body size over time and across dinosaur branches.

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 international team also included Andrea Cau, from the University of Bologna, Museo Geologico Giovanni Capellini, Darren Naish, Vertebrate Palaeontologist at the University of Southampton, Darren Naish, Vertebrate Palaeontologist at the University of Southampton.

The dinosaur lineage which evolved into birds shrank in body size continuously for 50 million years. From left to right are: the ancestral neotheropod (~220 Million years old), the ancestral tetanuran (~200 myo), the ancestral coelurosaur (~175 myo), the ancestral paravian (~165 myo), and Archaeopteryx (150 myo). Image: Davide Bonnadonna

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