Powered flight in feathered dinosaurs confirmed in Chinese fossils showing muscle imprints

Direct evidence for powered flight in feathered dinosaurs has finally been found using high-tech laser imaging.

Palaeontologists have previously determined that flying dinosaurs – ancestors of today’s birds – must have used shoulder muscles to power their wings’ upstrokes, and chest muscles to power downstrokes. However, this was based only on existing bony fossil evidence and comparison with living flying creatures.

Now, Chinese University of Hong Kong (CUHK) research has finally confirmed this by finding elusive soft tissues. The findings, which include the earliest soft anatomy profiles of flying dinosaurs, are published in Proceedings of the National Academy of Sciences (PNAS).

The study analysed more than 1,000 fossils of flying feathered dinosaurs that lived in the late Jurassic and early Cretaceous periods, found in north-eastern China.

Using a Laser-Stimulated Fluorescence (LSF) technique, the researchers targeted the shoulder and chest regions of the fossilised animals to study preserved soft tissue flight anatomy. Combining this data with skeletal reconstructions, the team validated the understanding of how the first birds took flight as paravian dinosaurs.

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“We have a good understanding of how living birds fly, but we know much less about how early fossil birds and their closest relatives flew since their soft tissues are rarely preserved,” says lead author Michael Pittman, an assistant professor at CUHK. “By using LSF imaging, my team can now see these elusive soft tissues that were only suggested previously by fossil bones.”

“The LSF data validated the ancestral flight condition of flying dinosaurs, where shoulder muscles powered the wing upstroke and chest muscles powered the wing downstroke, moving the field closer to accurately reconstructing early flight capability,” Pittman adds.

Also included in the study was an early beaked bird, Confuciusornis which lived 125 million years ago. With their reconstruction, the scientists could tell that this ancient bird had a weakly-constructed chest and strong shoulders.

“Our Confuciusornis reconstruction indicates the earliest evidence of upstroke-enhanced flight, which is very exciting,” says joint-corresponding author Professor Xiaoli Wang from Linyi University in China’s Shandong Province.

Some early flying birds and dinosaurs are missing a breastbone, or sternum. This strange quirk of evolution has been a mystery in palaeontology.

“We used our LSF data to propose that a more weakly constructed chest in early birds like Anchiornis was behind their lack of a breast bone,” says co-author Thomas G. Kaye from the Foundation for Scientific Advancement in Arizona. “They didn’t use their chest muscles enough for the sternum to be needed, so it was lost.”

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Many of the specimens displayed at the Shandong Tianyu Museum of Nature in Shandong Province. The museum is world-famous for its collection of feathered dinosaurs.

Museum Director and co-author Professor Xiaoting Zheng adds: “We are delighted that the team used data from more than 1,000 of our specimens to produce further significant advances in the study of flying dinosaurs. We look forward to sharing more exciting discoveries in the future.”