Evidence from the fingers of when flight began evolving in dinosaurs

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This research sprung from an investigation of whether or not birds had pronated (twisted inwards) their hands past what was found in their dinosaurian ancestors. They did not, but retained the same semi-pronated hands (a hand position with the palms pointing inwards if you point your arms anteriorly with the elbows downwards). More importantly, this investigation revealed that, even though the finger joints of birds had been described in functional terms by 1846, no one had ever asked whether Archaeopteryx or other avian dinosaurs possessed these finger joints. This neglect is surprising, because bird finger joints are highly conserved (unchanging) and adapted for flight. Therefore, the presence of even one typical bird finger joint in Archaeopteryx or other maniraptoran theropods would be highly suggestive of flight capability. When combined with our previous work (Hutson & Hutson, 2014, 2015b), we believe that our findings provide additional supportive evidence that many pennaraptoran theropods, like bats and pterosaurs, possessed wing joints stiffened in the semi-pronated plane to resist flight stresses.

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