Response to Serrano and Chiappe.

Summary In the recent study in Current Biology by Pei and colleagues 1 , we used two proxies — wing loading and specific lift — to reconstruct powered flight potential across the vaned feathered fossil pennaraptorans. The results recovered multiple origins of powered flight. We respectfully disagree with the criticism raised by Serrano and Chiappe 2 that wing loading and specific lift, used in sequence, fail to discriminate between powered flight and gliding. We will explain this in reference to our original conservative approach.