Getting Small the Key for Dinos that Became Birds

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The dinosaur lineage that 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 million years old), the ancestral coelurosaur (~175 million years old), the ancestral paravian (~165 million years old), and Archaeopteryx (150 million years old).
Davide Bonnadonna

How did some dinosaurs go from being impossibly huge, Earth-bound creatures to winged masters of the sky? The answer, a new study suggests, is simple: They got small, and kept on getting smaller.

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A study out of the University of Southampton just published in the journal Science involved an examination of 1,500 dinosaur traits by researchers, who reassembled the dinosaur family tree and used mathematical models to track adaptations and body size over time, and across branches of the dino family tree.

They observed that the therpod branch of dinosaurs, from which ultimately evolved modern birds, was the only branch that kept getting smaller in size, sustaining the shrinkage for 50 million years.

"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," said lead author Associate Professor Michael Lee, from the University of Adelaide's School of Earth and Environmental Sciences and the South Australian Museum, in a press release.

The adaptations taken on by early bird ancestors included such features as wishbones, feathers, and wings. These changes came "four times faster than other dinosaurs," observed the study's co-author Darren Naish, vertebrate palaeontologist at the University of Southampton.

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When it got right down to it, the researchers say, the branch of dinosaurs that became birds simply knew how to innovate, evolutionarily speaking, and then put the changes into a microwave on high. "Birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less evolvable relatives could not," said Lee.

"Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins," he added.