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Scansorial and aerial ability in Scansoriopterygidae and basal Oviraptorosauria

ABSTRACT Previously proposed hypothesis that known terrestrial and flightless members of the pennaraptoran clade Oviraptorosauria (Dinosauria: Theropoda) evolved from scansorial and volant ancestors is evaluated by reviewing publications on the phylogenetic position and morphology of the pennaraptoran clade Scansoriopterygidae. Publications on the phylogenetic relationships of basal members of the pennaraptoran clade Paraves and morphology of recently discovered basal paravians were also reviewed to re-evaluate a previously supported hypothesis that terrestrial and flightless members of the paravian clade Deinonychosauria evolved from scansorial and volant ancestors. Uncertainty about the phylogenetic position of Scansoriopterygidae among basal pennaraptorans suggests that scansoriopterygid morphology is close to the ancestral morphology of Pennaraptora. Functional morphology indicates that all known scansoriopterygids were capable of scansorial locomotion and gliding, but not active flight, suggesting that the most recent common ancestor of Pennaraptora was also a scansorial glider and therefore, supports the descent of known terrestrial and flightless Oviraptorosauria from scansorial and volant ancestors. This evolutionary scenario (supported by phylogenetic analyses and functional morphology) supports the evolution of pennaceous feathers as a flight adaptation and the ‘from the trees down’ hypothesis of bird flight evolution.