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Dinosaurs shrank for 50 million years to become birds

by Andy Coghlan

It took 50 million years of continual shrinking to turn massive, lumbering dinosaurs into the first small flying birds.

"No other dinosaur group has undergone such a long and extended period of miniaturisation," says Mike Lee of the South Australian Museum in Adelaide. “Statistically this trend was far stronger than by chance, analogous to flipping a coin a dozen times and getting all heads.”

Lee and his colleagues have performed the most comprehensive analysis yet of fossil theropods, the two-footed meat-eating dinosaurs, like Velociraptor, from which birds evolved. They have charted how 224-million-year-old dinosaurs weighing 238 kilograms evolved into proto-birds, including Archaeopteryx, that weighed just 0.8 kg.

The analysis reveals that the ancestors of birds shrank without interruption. “What was impressive was the consistency of the size change along the dinosaur-to-bird transition, with every descendant smaller than its ancestor,” says Lee. Getting smaller must have offered advantages at every turn…

(read more: New Scientist)

illustration by Davide Bonnadonna

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