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| Plumadraco bankoorum Clark, O’Connor, X. Wang, Y. Wang, Pruett-Jones, Zhang, X.Wang, Zheng & Zhou, 2026 Illustration: Ville Sinkkonen |
Abstract
Bird diversity is reflected in the abundance and variety of extraordinary plumages. Some of these include elongate, ornamental tail feathers that are typically attributed to either intraspecific communication in monomorphic species or sexual selection in sexually-dimorphic ones. Enantiornithines (Aves: Ornithothoraces) were the most diverse group of birds during the Cretaceous. Importantly, some enantiornithine fossils preserve soft tissues, most often in the form of feathers surrounding the body. Unlike any living bird, many enantiornithine specimens lack tail feathers (rectrices) all together, with the tail region consisting entirely of contour feathers. However, when present, enantiornithine rectrices typically consist of a pair of elongate, ornamental feathers with unusually wide rachises, referred to as rachis-dominated feathers. Here we describe Plumadraco bankoorum gen. et sp. nov., a new bohaiornithid enantiornithine with a pair of exceptionally long rectrices. These tail feathers measure twice the individual’s body length, ending in proportionally small pennaceous rackets, thus adding to the growing diversity of these unusual feathers. The fine preservation of these tail feathers, in comparison to other enantiornithine rectrices, reveals previously unrecognized structural variation that hints at their potential function in courtship displays. Although ornamental feathers in enantiornithines are widely considered sexually dimorphic, determining the selection pressures that shaped them is difficult due primarily to limited soft tissue data. Enantiornithine rectrices are likely the result of an interplay between both sexual and naturally selective pressures, similar to the processes which produce analogous structures in birds today.
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| Plumadraco bankoorum. The skull of STM11−4. (A) Photo of fossil specimen and (B) a corresponding line drawing. Well preserved bones are colored white, crushed or poorly preserved bones (or portions of bones) are grey, and preserved soft tissues are brown. Abbreviations: at, atlas; cev, cervical vertebrae; dn, dentary; fe, feathers; fp, frontal process of the premaxilla; fe, feather; fr, frontal; l, left; mx, maxilla; ns, nasal; pmx, premaxilla; pr, parietal; r, right; su, surangular; to, tooth. Scale bar 10 mm. |
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| Plumadraco bankoorum. Specimen STM11−4 (A) The holotype specimen of Plumadraco, (B) a closer view of the body and, (C) a line drawing of the same portion of the body shown in B. Well preserved bones are colored white, crushed or poorly preserved bones (or portions of bones) are grey, and preserved soft tissues are brown. The extent of the feather traces are denoted by the thin black outline around the body. Potential outline or crural feather present along the cranial face of the tibia. Abbreviations: al, alula; cev, cervical vertebrae; co, coracoid; fm, femur; fu, furcula; hu, humerus; il, ilium; is, ischium; ma, manus; ph, phalanges (of the peds); pu, pubis; py, pygostyle; ri, rib(s); ra, radius; sc, scapula; sk, skull; sp, sternal plate; sy, synsacrum; tb, tibia; tmt, tarsometatarsus; tf, tail feathers; tv, thoracic vertebrae; ul, ulna. Scale bar (A, C) equals 50 mm. |
Systematic paleontology
Aves Linnaeus, 1758
Pygostylia Chiappe et al., 2002
Ornithothoraces Chiappe, 1995
Enantiornithes Walker, 1981
Plumadraco bankoorum gen. et sp. nov.
Holotype. STM11−4 is a complete, articulated specimen preserved in a single slab primarily in dorsal aspect with feathers preserved around the head, body, wings, and tail.
Locality and horizon. Near Xiaotaizi Village, Jianchang County, Liaoning Province, Jiufotang Formation, 121 Ma (Lower Aptian).
Diagnosis: Mid-sized [112–144 g, similar to some extant turdids (e.g., Cochoa, Turdus) and meliphagids (e.g., Anthochaera) enantiornithine (ventral margin of the furcula wider than dorsal margin; acrocoracoid, glenoid, and scapular cotyla omal-sternally aligned; minor metacarpal extending distally farther than the major metacarpal; metatarsal IV thinner than metatarsals II and III with the trochlea reduced to a single condyle; and a J-shaped metatarsal I), belonging to the family Bohaiornithidae (basally robust, apically tapered dentition; unforked dentary- surangular articulation; proportional width of the coracoid’s sternal margin; caudolateral projection of the sternal plate’s lateral trabeculae; well-developed abruptly terminating deltopectoral crest; robust pedal unguals), with the unique combination of the following features: corpus of the premaxillae dorsoventrally deeper than the dentaries; rostral ~80% of the dentary with parallel dorsal and ventral margins; tip of dentary is rostrodorsally tapered; at least nine sacral vertebrae; caudally-oriented lateral trabeculae of the sternum with asymmetrical, fan-shaped distal expansions; phalanx I of the manual digit craniocaudally thin; weakly curved pedal unguals; RDFs approximately twice body length.
Etymology. “Pluma”, Latin for feather, and “draco”, Latin for dragon. In the theme of avian biology and evolution, the specific name, “bankoorum”, honors Winston E. and Paul C. Banko. Together, their momentous life-long efforts have significantly contributed to our understanding of avian biology and conservation, particularly across the Hawaiian archipelago. Plumadraco bankoorum, the Banko’s feather dragon.
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| B) Finely-preserved structures present in the proximal portion of the right RDF of Plumadraco bankoorum, C) and the preserved racket showing the differentiated barbs and the reduction, and eventual complete termination, of the central support structures (i.e., ramus and medial stripe). (D) The unique, undifferentiated barbs of the occipital plumes of Pteridophora alberti (King-of-Saxony Bird-of-Paradise) (FMNH 280831) forming tab-like laminated sheets. These structures may be uniquely analogous to the lateral margins (ribbon-like sheets) of enantiornithine RDFs preceding the distal ornaments. (E) An in-life restoration of Plumadraco. Illustration by Ville Sinkkonen. |
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| Results of phylogenetic analyses suggest Plumadraco belongs to the diverse Bohaiornithidae. |
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| male and female Plumadraco bankoorum Illustration: Ville Sinkkonen |
Alexander D. Clark, Jingmai K. O’Connor, Xiaoli Wang, Yan Wang, Stephen Pruett-Jones, Xiangyu Zhang, Xing Wang, Xiaoting Zheng and Zhonghe Zhou. 2026. Hyperelongate Ornamental Tail Feathers in A New early Cretaceous enantiornithine Bird. PLoS One 21(5): e0347641. DOI: doi.org/10.1371/journal.pone.0347641 [May 27, 2026]
