A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early paravian evolution

Abstract

The Jurassic Yanliao theropods have offered rare glimpses of the early paravian evolution and particularly of bird origins, but, with the exception of the bizarre scansoriopterygids, they have shown similar skeletal and integumentary morphologies. Here we report a distinctive new Yanliao theropod species bearing prominent lacrimal crests, bony ornaments previously known from more basal theropods. It shows longer arm and leg feathers than Anchiornis and tail feathers with asymmetrical vanes forming a tail surface area even larger than that in Archaeopteryx. Nanostructures, interpreted as melanosomes, are morphologically similar to organized, platelet-shaped organelles that produce bright iridescent colours in extant birds. The new species indicates the presence of bony ornaments, feather colour and flight-related features consistent with proposed rapid character evolution and significant diversity in signalling and locomotor strategies near bird origins.

Fig. 1

Caihong juji holotype specimen (PMoL-B00175). Photographs of the slab (a) and counter slab (b) and line drawing (c) of the specimen based on both slabs. Photograph (d) and line drawing (e) of a composite of the rostrum of the skull and mandible exposed on the counter slab and the post-rostrum cranium exposed on the slab. Arrows indicate lacrimal crests. Question mark indicates uncertain identification. Scale bars: 10 cm a–c, 1 cm d and e. aof antorbital fenestra, cav caudal vertebra, cev cervical vertebra, dr dorsal rib, dv dorsal vertebra, ect ectopterygoid, emf external mandibular fenestra, en external naris, f feather, fu furcula, ga gastralia, hy hyoid, il ilium, is ischium, la left angular, lar left articular, lc left coracoid, lcr lacrimal crest, ld left dentary, lf left, frontal, lfe left femur, lh left humerus, lj left jugal, ll left lacrimal, lma left maxilla, lm left manus, ln left nasal, lp left pes, lpa left palatine, lpo left postorbital, lq left quadrate, lqj left quadratojugal, lr left radius, ls left scapula, lsp left splenial, lsa left surangular, lsq left squamosal, lt left tibiotarsus, lu left ulna, ma mandible, mf maxillary fenestra, o orbit, p parietal, pm premaxilla, pt pterygoid, pu pubis, rar right articular, rc right coracoid, rd right dentary, rfe right femur, rh right humerus, rm right manus, rp right pes, rpra right prearticular, rq right quadrate, rr right radius, rs right scapula, rt right tibiotarsus, ru right ulna, scl sclerotic bones, sk skull, sy synsacrum

Fig. 2

Photographs of the vertebral column of Caihong juji. a Posterior cervical vertebrae in dorsal view; b middle dorsal vertebrae in lateral view; c anterior caudal vertebrae in dorsal view; d middle caudal vertebrae in lateral view; e posterior caudal vertebrae in lateral view. Scale bars: 0.5 cm

Fig. 3

Photographs of the pectoral girdle and limbs of Caihong juji. a Right scapula and coracoid in medial and proximal views; b right forelimb; c left manus; d left and right hind limbs. Scale bar: 1 cm in a, c, and 5 cm in b, d

Fig. 4

Feathers preserved in Caihong juji. Feathers attached to the neck: (a) pennaceous feathers and (b) down-like feather; (c) feathers attached to the chest and trunk region; (d) primary or secondary remige near the carpal joint; (e) alula; (f) pennaceous feather on the tibiotarsus; (g) anterior rectrix; (h) posterior rectrix; (i) middle rectrix; (j) close-up of barbs and barbules. Scale bars are 0.2 cm in a, b, j; 0.5 cm in d, e, f, g, h; and 1 cm in c, i, respectively. Arrows in j indicate barbules of a rectrix

Fig. 5

Platelet-like nanostructures in Caihong juji and melanosomes in iridescent extant feathers. a–d Fossilized nanostructures from Caihong feathers preserved as molds in a neck feather (a) and three-dimensional preservation in a neck feather, with SEM stage rotated 45° to show 3D platelet morphology (b), a back feather with SEM stage at 0° (c) and a neck feather showing nanostructure packing (d); e Anna’s hummingbird (Calypte anna) showing overlapping melanosomes within a feather barbule; f white-tailed starfrontlet (Coeligena phalerata) showing stacking and interior morphology (air bubbles) of melanosomes in a feather barbule; g black-tailed trainbearer (Lesbia victoriae) showing exterior surface and morphology of isolated melanosomes in a feather barb; h moustached treeswift (Hemiprocne mystacea) showing densely packed melanosomes in the barbule of a crown feather. Inset in d illustrates 3D stacking of platelet-shaped nanostructures. All scale bars: 1000 nm. Photo credits: Chao PC (e, license CC BY-2.0, https://creativecommons.org/licenses/by/2.0/legalcode), Misty Vaughn f, Lip Kee (g, license CC BY-SA 2.0, https://creativecommons.org/licenses/by-sa/2.0/legalcode), Lip Kee (h, CC BY-SA 2.0, https://creativecommons.org/licenses/by-sa/2.0/legalcode)

Fig. 6

Analyses of nanostructure shape diversity and phylogenetic position of Caihong juji. a Mean length and diameter measurements for nanostructures from various body regions in Caihong juji (red), Anchiornis huxleyi (grey) and Microraptor (black). Rarefaction analyses show that sampling of the fossil taxa is appropriate to determine significant differences: Anchiornis shows significantly more nanostructure diversity than either Caihong or Microraptor (Supplementary Fig. 13). b Morphospace plots of raw nanostructure measurements for Caihong juji relative to extant avian groups with platelet-like melanosomes (orange: hummingbirds, green: swifts, blue: trumpeters and trogons, grey: other non-platelet avian melanosomes). Contour lines show 2D density of measurements. Numbers give proportional overlap (∩) between Caihong juji (red) and each group (Methods). c Simplified coelurosaurian phylogeny (strict consensus of 192 most parsimonious trees from the primary analysis) showing the recovered position of Caihong juji (Supplementary Note 3; Supplementary Figs. 18 and 19). Additional assessments of the taxon utilizing another recent data set recover an Anchiorninae clade as a part of Troodontidae (Supplementary Note 3; Supplementary Figs. 20, 22). Photo credits: Fred Wierum (Microraptor, CC BY SA 4.0, https://creativecommons.org/licenses/by-sa/4.0/legalcode), Dick Daniels (Trumpeter, CC BY SA 3.0, https://creativecommons.org/licenses/by-sa/3.0/legalcode), Alan Vernon (Red-tailed hawk, CC BY 2.0, https://creativecommons.org/licenses/by/2.0/legalcode), T R Shankar Raman (Glossy swiftlet, CC BY SA 4.0, https://creativecommons.org/licenses/by-sa/4.0/legalcode), Nobu Tamura (Anchiornis, CC BY 3.0, https://creativecommons.org/licenses/by/3.0/legalcode), J. Clarke (Caihong, modified from original artwork by Velizar Simeonovski, used with permission), Robert McMorran/USFWS (Anna’s hummingbird, CC BY 2.0, https://creativecommons.org/licenses/by/2.0/legalcode)