overall as in derived troodontids, despite the presence of basal traits. An ancestral state reconstruction conducted along with the phylogenetic analysis (results labelled in the above phylogenetic tree) suggests that wing feather asymmetry evolved only once, at the last common ancestor of the Paraves. Asymmetrical tail feathers would then also have evolved once, at the common ancestor of all paravians excluding scansoriopterygids and avialans. However, given the uncertainty of whether dromaeosaurids possessed asymmetrical wing feathers, the support for a single emergence of asymmetrical wing feathers in the common ancestor of the Paraves is equivocal, the alternative scenario that it evolved twice being plausible. The distinct possibility thus remains that troodontids had asymmetrical tail feathers but symmetrical arm feathers, suggesting that asymmetry in the tail appeared first, but this is not supported by the ancestral state reconstruction. Paleobiology Jianianhualong preserves the first evidence of feathers in an unquestionable troodontid, with the troodontid affinities of taxa such as Anchiornis, Eosinopteryx, Jinfengopteryx, and Xiaotingia having been questioned by various studies. Additionally, Jianianhualong represents the first record of asymmetrical feathers among troodontids, thus making troodontids the second group among non-avialan theropods to possess asymmetrical feathers; asymmetrical arm feathers are found in the microraptorians Microraptor, Changyuraptor, and possibly Zhenyuanlong. Asymmetrical feathers are correlated with flight capabilities among paravians, and their emergence marked a major step in the evolution of modern avian feathers. This trait may have been selected for due to its augmentation of locomotion on the ground or in the air. However, the presence of asymmetrical feathers in Jianianhualong does not guarantee that it was capable of either gliding or powered flight. The feathers in the tail of Jianianhualong could certainly have functioned in either maintaining feather stability (the barbs of the leading edge, having a low angle of 10°, augmented the vane's rigidity) or controlling airflow (through the variation of the feathers' blade pitch). However, these feathers differ from those of modern birds in that the barbs of the trailing edge also have a relatively low angle of approximately 15°. Thus, aerodynamically speaking, the feathers in the tail of Jianianhualong likely did not have the same function as those of modern birds. Regardless, the subtriangular outline of the tail frond, as well as the slots separating the tips of individual feathers, would have provided drag reduction when the tail was in use. Paleoecology After Mei, Sinovenator, Sinusonasus, and Jinfengopteryx, Jianianhualong is the fifth