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| Zhengheornis buyu Wang, Tang, Deng, Dong, L. Xu, X. Xu, M. Lin, Du, G. Lin, Chen, Zhang & Zhou, 2026 |
Abstract
The evolutionary assembly of the flight-adapted bird body plan encompasses some of the most profound morphological changes in terrestrial vertebrate history. Beyond feathered wings, the short pygostyle-bearing tail has been pivotal to the clade’s ecological success. However, transition from the long bony tail to the short pygostyle-bearing tail remains a mystery, hindered by the scarcity of early branching avialans with transitional morphologies. Here, we report on a new avialan, Zhengheornis buyu, gen. et sp. nov., from the Upper Jurassic of southeastern China, suggesting that the vertebral reduction and shortening preceded pygostyle fusion in early avialan evolution, providing critical evidence for the stepwise evolution of the bird tail. Z. buyu is smaller than all known non-pygostylian paravians, expanding the species and body size diversity of stemward taxa.
Systematics
Theropoda Marsh, 1881
Maniraptora Gauthier, 1986
Avialae Gauthier, 1986
Zhengheornis buyu gen. et sp. nov.
Etymology: “Zhenghe” (Mandarin), referring to Zhenghe Country, where the holotype specimen was found; “ornis,” bird (Greek); “buyu,” unexpected (Mandarin), from the ancient Chinese book Guoyu, referring to the unique tail and pelvic morphologies preserved in this species.
Holotype: Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) V34168, an articulated and partially complete skeleton (most limb bones are preserved as molds) with feathers preserved on a slab and counter slab (Fig. 1, figs. S1 and S2, and table S1).
Locality and horizon: Near Yangyuan Village, Zhenghe Country, Nanping City, Fujian Province; Upper Jurassic, Nanyuan Formation [Tithonian stage].
Diagnosis: IVPP V34168 is distinguishable from all other paravians in the following combination of characters (*denotes probable autapomorphy): short tail comprising 15 vertebrae that is shorter than the hindlimb (combined length of femur, tibia, and metatarsal III)*; middle and posterior caudal vertebrae less elongate (opposite to the condition in other long tailed avialans); final two caudal vertebrae box-like*; manual phalanx III-1 shorter than III-2, opposite to the condition in Archaeopteryx and Fujianvenator [the three manual digits of maniraptorans are here identified as I, II, and III, as in (Tamura, et al. 2011)]; manual phalanx III-3 50% longer than III-2 (the length ratio greater than 2 in Anchiornis and Archaeopteryx); slender ischium that has a knob-like, distally located obturator process and lacks the posterior process*; short fibula that terminates far proximal to the ankle; metatarsal I that articulates at the distal third of metatarsal II; metatarsal II that ends far proximal to metatarsal III trochlea; short hallux with an ungual that is smaller than that of other pedal digits; and robust digit II that has the longest non-ungual (II-2) and ungual pedal phalanges.
Min Wang, Jianrong Tang, Ke Deng, Liping Dong, Liming Xu, Xing Xu, Min Lin, Honggang Du, Ganmin Lin, Runsheng Chen, Chi Zhang and Zhonghe Zhou. 2026. Jurassic Avialan reveals stepwise Evolution of Bony Tail in Birds. Science Advances. 12(27); DOI: doi.org/10.1126/sciadv.aeb5202 [1 Jul 2026]
