Serrano and Chiappe 2021 seek to
"weaken prior evidence"
supporting a multiple origin of powered flight. They wrote, “Feathered dinosaurs discovered during the last decades have illuminated the transition from land to air in these animals, underscoring a significant degree of experimentation in wing-assisted locomotion around the origin of birds. Such evolutionary experimentation led to lineages achieving either wing-assisted running, four-winged gliding, or membrane-winged gliding.”
Oops. They just undermined their argument. No one has yet produced four long bones per forelimb (rather than the typical three found in all limbed tetrapods) in scansoriopterygids like Ambopteryx and Yi qi.
“Birds are widely accepted as the only dinosaur lineage that achieved powered flight, a key innovation for their evolutionary success. However, in a recent paper in Current Biology, Pei and colleagues disputed this view. They concluded that three other lineages of paravian dinosaurs (those more closely related to birds than to oviraptorosaurs) — Unenlagiinae, Microraptorinae and Anchiornithinae — could have evolved powered flight independently. While we praise the detailed phylogenetic framework of Pei and colleagues and welcome a new attempt to understand the onset of flight in dinosaurs, we here expose a set of arguments that significantly weaken their evidence supporting a multiple origin of powered flight. Specifically, we maintain that the two proxies used by Pei and colleagues to assess powered flight potential in non-avian paravians — wing loading and specific lift — fail to discriminate between powered flight (thrust generated by flapping) and passive flight (gliding).”
Once again… you heard it here first (“fail to discriminate between powered flight and passive flght” see links above).
Pittman et al. 2021 responded
“In the recent study in Current Biology by Pei and colleagues, 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 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.”
“Will explain this” does not explain this. So this abstract is more of a tease.
And, of course, a valid phylogenetic context, employing more than one Solnhofen bird, is really all you need (Fig. 1).
Pei R et al. 2020. Potential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds. Current Biology online here.
Pittman M et al. (8 co-authors) 2021. Response to Serrano and Chiappe.
Current Biology 31(8): R372-R373 doi: https://doi.org/10.1016/j.cub.2021.03.059
Serrano FJ and Chiappe LM 2021. Independent origins of powered flight in paravian dinosaurs? Current Biology 31(8): R370-R372