The plumage of Longipteryx (Aves: Enantiornithes)

Abstract The 121 Ma Jiufotang Formation in northeastern China contains the greatest avifaunal diversity of any known Mesozoic deposit. Enantiornithine birds dominate this formation with hundreds of exceptionally preserved specimens often bearing soft tissues such as feather traces. Of the described enantiornithines from these deposits, Longipteryx is the most abundant, easily identified by its elongate rostrum and distally restricted, proportionally large teeth. Although numerous specimens of this taxon have been described, data concerning its plumage is surprisingly lacking. Here, we qualitatively describe two new Longipteryx chaoyangensis specimens preserving feathers across the body, including the best evidence of wing feather (remex) morphology thus far for this taxon. The folded wing of Longipteryx has a predominantly linear trailing margin and primary feathers nearly twice the length of the secondaries. Based on remex lengths and the preserved position of the forelimbs, the outstretched wings of Longipteryx may have been intermediate (i.e., a wing profile between the broad morphology inferred for some enantiornithines and the elongate shape reconstructed for Confuciusornis ), superficially resembling extant bird species whose wing profiles are associated with bounding, continuous-flapping, and flap-gliding flight. These flight strategies have been previously predicted for some enantiornithines based also on remex and skeletal morphometrics. Additionally, all known Longipteryx specimens lack traces or impressions of tail feathers (rectrices) altogether. Most enantiornithines with preserved rectrices have a pair of elongate ornamental feathers. It is thus unusual and notable that these appear to be absent in both sexes in Longipteryx.