Saturday, November 16, 2019

[Paleontology • 2019] Fukuipteryx prima • An Unusual Bird (Theropoda, Avialae) from the Early Cretaceous of Japan suggests Complex Evolutionary History of Basal Birds

Fukuipteryx prima
Imai, Azuma, Kawabe, Shibata, Miyata, Wang & Zhou, 2019

(artwork by M. Yoshida)

The Early Cretaceous basal birds were known largely from just two-dimensionally preserved specimens from north-eastern China (Jehol Biota), which has hindered our understanding of the early evolution of birds. Here, we present a three-dimensionally-preserved skeleton (FPDM-V-9769) of a basal bird from the Early Cretaceous of Fukui, central Japan. Unique features in the pygostyle and humerus allow the assignment of FPDM-V-9769 to a new taxon, Fukuipteryx prima. FPDM-V-9769 exhibits a set of features comparable to that of other basalmost birds including Archaeopteryx. Osteohistological analyses indicate that FPDM-V-9769 is subadult. Phylogenetic analyses resolve F. prima as a non-ornithothoracine avialan basal to Jeholornis and outgroup of the Pygostylia. This phylogenetic result may imply a complex evolutionary history of basal birds. To our knowledge, FPDM-V-9769 represents the first record of the Early Cretaceous non-ornithothoracine avialan outside of the Jehol Biota and increases our understanding of their diversity and distribution during the time.

Figure 1: FPDM-V-9769. a Photograph. A box indicates where a sample was taken for osteohistological analyses. b Schematic line drawing of the skeletons. Abbreviations: cev cervical vertebra, co coracoid, dv dorsal vertebra, fe femur, fu furcula, hu humerus, il ilium, mc metacarpal, md manual digit, py pygostyle, ra radius, sv sacral vertebra, ti tibia, ul ulna. Scale bars equal 3 cm in a and b

Figure 2: Reconstructions and restoration. a–c Skeletal reconstructions of FPDM-V-9769 in cranial (a), dorsal (b), and left-lateral (c) views. d Life restoration of Fukuipteryx prima (artwork by M. Yoshida). One side of a cube in each image equals 1 cm

Systematic palaeontology
Theropoda Marsh, 1881
Maniraptora Gauthier, 1986
Avialae Gauthier, 1986

Fukuipteryx prima gen. et sp. nov.

Etymology: Fukui refers to Fukui Prefecture in central Japan, where the specimen was collected, and pteryx (Latin) for wingprima (Latin) for primitive, as the species exhibits several primitive morphological features among fossil birds.

Diagnosis: A pigeon-sized non-ornithothoracine avialan with the following autapomorphies: semicircular depression on the craniodorsal corner of the humeral head, dorsally bowed humeral shaft, and robust pygostyle with incipient spinal processes and paddle-like structure at the distal end.

Holotype: FPDM-V-9769 (FPDM: Fukui Prefectural Dinosaur Museum, Fig. 1), a disarticulated but closely associated skeleton, including right surangular; two cervicals; four dorsals including two nearly complete ones, an isolated centrum, and incomplete vertebral arch; incomplete synsacrum composed of two sacrals; five caudals; pygostyle; several dorsal ribs; incomplete furcula; incomplete left and right coracoids; incomplete right ilium; forelimbs including left humerus, incomplete left and complete right ulna, complete left and incomplete right radius, right major metacarpal, left minor metacarpal, left alular digit 1, left major digits 2 and 3, minor digits 3 and 4; and hindlimbs including left and right femur; left and right incomplete tibia; and variably preserved metatarsals II (left), III (incomplete left), and IV (complete left and incomplete right).

Type locality and horizon: Kitadani Dinosaur Quarry in the northern part of the city of Katsuyama, Fukui, Japan (Supplementary Fig. 1); the Lower Cretaceous Kitadani Formation (Aptian)23 (see Supplementary Notes for further details).

Takuya Imai, Yoichi Azuma, Soichiro Kawabe, Masateru Shibata, Kazunori Miyata, Min Wang and Zhonghe Zhou. 2019. An Unusual Bird (Theropoda, Avialae) from the Early Cretaceous of Japan suggests Complex Evolutionary History of Basal Birds. Communications Biology. 2: 399.