Shrinking gave bird ancestors an edge

"Birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less evolvable relatives could not," says Michael Lee. (Credit: Suzanne Phillips/Flickr)

50 million years of shrinking turned huge, meat-eating, ground-dwelling dinosaurs into agile flying birds, report researchers.

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

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

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“These bird ancestors also evolved new adaptations, such as feathers, wishbones, and wings, four times faster than other dinosaurs,” says coauthor Darren Naish, vertebrate paleontologist at the University of Southampton.

“Birds evolved through a unique phase of sustained miniaturization in dinosaurs,” says lead author Michael Lee of 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.”

Coauthor Gareth Dyke, senior lecturer in vertebrate paleontology at the University of Southampton, adds that “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 over 1,500 anatomical traits of dinosaurs to reconstruct their family tree. The researchers used mathematical modeling to trace evolving adaptions and changing body size over time and across dinosaur branches.

The study concludes 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 Lee.

Source: University of Southampton