ArticlePDF Available

Pterosaur integumentary structures with complex feather-like branching

Authors:

Abstract and Figures

Pterosaurs were the first vertebrates to achieve true flapping flight, but in the absence of living representatives, many questions concerning their biology and lifestyle remain unresolved. Pycnofibres—the integumentary coverings of pterosaurs—are particularly enigmatic: although many reconstructions depict fur-like coverings composed of pycnofibres, their affinities and function are not fully understood. Here, we report the preservation in two anurognathid pterosaur specimens of morphologically diverse pycnofibres that show diagnostic features of feathers, including non-vaned grouped filaments and bilaterally branched filaments, hitherto considered unique to maniraptoran dinosaurs, and preserved melanosomes with diverse geometries. These findings could imply that feathers had deep evolutionary origins in ancestral archosaurs, or that these structures arose independently in pterosaurs. The presence of feather-like structures suggests that anurognathids, and potentially other pterosaurs, possessed a dense filamentous covering that probably functioned in thermoregulation, tactile sensing, signalling and aerodynamics. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.
This content is subject to copyright. Terms and conditions apply.
1
Pterosaur integumentary structures with complex feather-like branching 1
Zixiao Yang1, Baoyu Jiang1, Maria E. McNamara2, Stuart L. Kearns3, Michael 2
Pittman4, Thomas G. Kaye5, Patrick J. Orr6, Xing Xu7, Michael J. Benton3 3
4
1. Center for Research and Education on Biological Evolution and Environments, 5
School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, 6
China 7
2. School of Biological, Earth and Environmental Sciences, University College Cork, 8
Cork T23 TK30, Ireland 9
3. Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK 10
4. Vertebrate Palaeontology Laboratory, Department of Earth Sciences, University of 11
Hong Kong, Pokfulam, Hong Kong, China 12
5. Foundation for Scientific Advancement, Sierra Vista, Arizona USA 13
6. UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4 14
D04V1W8, Ireland 15
7. Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate 16
Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, 17
China 18
19
Pterosaurs were the first vertebrates to achieve true flapping flight, but in the 20
absence of living representatives, many questions concerning their biology and 21
lifestyle remain unresolved. Pycnofibres, the integumentary coverings of 22
pterosaurs, are particularly enigmatic: although many reconstructions depict 23
2
fur-like coverings composed of pycnofibres, their affinities and function are not 24
fully understood. Here we report the preservation in two anurognathid pterosaur 25
specimens of morphologically diverse pycnofibres that show diagnostic features 26
of feathers, including non-vaned grouped filaments and bilaterally branched 27
filaments, hitherto considered unique to maniraptoran dinosaurs, and preserved 28
melanosomes with diverse geometries. These findings could imply that feathers 29
had deep evolutionary origins in ancestral archosaurs, or that these structures 30
arose independently in pterosaurs. The presence of feather-like structures 31
suggests that anurognathids, and potentially other pterosaurs, possessed a dense 32
filamentous covering that likely functioned in thermoregulation, tactile sensing, 33
signalling, and aerodynamics. 34
Feathers are the most complex integumentary appendages in vertebrates1. Most 35
feathers in modern birds possess an axial shaft from which branch lateral barbs and 36
barbules. Much is known about the anatomy, developmental biology, and genomic 37
regulation of these structures, but their deep evolutionary origin is controversial2-4. 38
Feathers and feather-like integumentary structures have been reported in many 39
theropod dinosaurs (including birds)3,5 and ornithischians such as Psittacosaurus6, 40
Tianyulong7, and Kulindadromeus8. Feather-like or hair-like structures, termed 41
pycnofibres9, have also been reported in several pterosaur specimens9-13, but their 42
nature is not resolved. 43
Here we report remarkably well-preserved pycnofibres in two anurognathid 44
pterosaurs and demonstrate, using evidence from morphology, chemistry and 45
3
macroevolutionary analyses, that the preserved pycnofibres bear key features of 46
feathers: monofilaments, two types of non-vaned grouped filaments, bilaterally 47
branched filaments that were previously considered unique to maniraptoran dinosaurs, 48
and preserved melanosomes with diverse geometries. Both specimens studied are 49
from the Middle–Late Jurassic Yanliao Biota (ca. 165–160 Mya14). NJU–57003 50
(Nanjing University) is a newly excavated specimen from the Mutoudeng locality and 51
CAGS–Z070 (Institute of Geology, Chinese Academy of Geological Sciences), which 52
has been noted previously13, is from the Daohugou locality. Both specimens are 53
near-complete and well-articulated, with extensive soft tissues (Figs. 1 and 2, and 54
Supplementary Figs. 1–5). Both specimens are identified as anurognathids17 (see 55
Supplementary text for osteological descriptions). 56
Preserved soft tissues include structural fibres (actinofibrils) and pycnofibres. 57
Structural fibres, common in the pterosaur wing membrane9,12,18, are observed only in 58
the posterior portion of the uropatagium in CAGS–Z070 (Fig. 1op). As reported 59
elsewhere, they are parallel to subparallel and closely packed. Individual fibres are 60
0.08–0.11 mm wide (ca. 5 fibres per mm) and at least 1.9 mm long. Pycnofibres are 61
preserved extensively in both pterosaur specimens (especially CAGS–Z070; Figs. 1 62
and 2, and Supplementary Figs. 1, 4 and 5) and are discriminated from structural 63
fibres based on their curved morphology and overlapping arrangement. In the 64
posterior portion of the uropatagium in CAGS–Z070, pycnofibres co-occur with 65
structural fibres; oblique intersections reflect superposition of these features during 66
decay (Fig. 1op). 67
4
Pycnofibres are categorized here into four types. Type 1 occurs around the head, 68
neck, shoulder, torso, all four limbs and tail of both specimens (Figs. 1ce, op, 2bc 69
and f). It comprises curved monofilaments that are 3.5–12.8 mm long and 70–430 μm 70
wide. Some short, distally tapering examples discriminate between dark-toned lateral 71
margins and light-toned axial regions, especially near the filament base where the 72
light-toned axis is wider, suggesting a tube-like morphology (Fig. 1ce). Type 2 is 73
preserved in the neck, proximal forelimb, plantar metatarsus and proximal tail regions 74
of CAGS–Z070. It consists of bundles of curved filaments of similar length that 75
appear to form brush-like structures at the distal ends of thicker filaments (2.0–13.8 76
mm long and 80–180 μm wide) (Fig. 1fh). The latter may represent individual thick 77
filaments or fused proximal regions of thinner distal filaments. Type 3 occurs around 78
the head of CAGS–Z070. It comprises straight to slightly curved, distally tapered, 79
central filaments (4.5–7.0 mm long and 50–450 μm wide) with short lateral branches 80
that diverge from the central filament near the midpoint (Fig. 1ik). There are five 81
Type 3 filaments identified on the head, next to five similar filaments likely of the 82
same nature but obscured by overlapping filaments (Supplementary Fig. 5b). Type 4 83
occurs on the wing membrane of both specimens. It comprises tufts of curved 84
filaments (2.5–8.0 mm long and 70–130 μm wide) that diverge proximally (Figs. 1ln 85
and 2de), in contrast to the clear separation between Type 1 filaments (Fig. 1op). 86
Filamentous integumentary structures in extant and fossil vertebrates commonly 87
contain melanin-bearing organelles (melanosomes). Scanning electron microscopy 88
(SEM) of the filamentous structures of NJU–57003 reveals densely packed 89
5
microbodies 0.70 ± 0.11 μm long and 0.32 ± 0.05 μm wide (Fig. 2gh, Supplementary 90
Figs. 4af, 6 and 7, and Supplementary Table 2). As with most melanosome-rich 91
fossil feathers19-21, energy dispersive X-ray spectroscopy (EDS) spectra of the 92
filaments are dominated by a major peak for carbon (Supplementary Fig. 8). These 93
carbonaceous microbodies resemble fossil melanosomes in terms of their geometry, 94
dense packing, parallel alignment relative to the long axis of the integumentary 95
structure (i.e. barbules in Paraves), and preservation within the matrix of the filament 96
(see Supplementary text). Most of the microbodies are oblate and morphologically 97
similar to those that are usually interpreted as phaeomelanosomes in fossils19 (Fig. 2h). 98
Rod-shaped examples, usually interpreted as eumelanosomes in fossils19 (Fig. 2g), are 99
rare. 100
Fourier transform infrared spectroscopy (FTIR) of samples of pterosaur filaments 101
shows four major peaks unique to the filaments (Fig. 2i). These peaks are consistent 102
with the absorption regions of amide I at ca. 1650 cm1 (principally the C=O 103
asymmetric stretching vibration with some C–N bending), amide II at ca. 1540 cm1 104
(a combination of N–H in-plane bending and C–N and C–C stretching as in indole 105
and pyrrole in melanin and amino acids), and aliphatic C–H stretching at 2850 cm1 106
and 2918 cm1 22. These peaks also occur in spectra obtained from extant feathers21,23, 107
fossil feathers of the paravian Anchiornis20, and melanosomes isolated from human 108
hair24. Further, spectra of the pterosaur filaments more closely resemble those of 109
pheomelanin-rich red human hair in the stronger absorption regions at ca. 2850 cm1
110
and 2918 cm1 and higher resolution in the region ca. 1500–1700 cm1 than those 111
6
from eumelanin-rich black human hair and the ink sac of cuttlefish24. This, together 112
with the SEM results, suggests that the densely packed microbodies in the pterosaur 113
filaments are preserved melanosomes. The amide I peak at 1650 cm1 is more 114
consistent with α-keratin (characteristic of extant mammal hair25) than β-keratin (the 115
primary keratin in extant avian feathers22,26). This signal may be original or diagenetic; 116
the molecular configuration of keratin26 and other proteins27 can alter under 117
mechanical stress and changes in hydration levels. 118
The ultrastructural and chemical features of the pterosaur filaments confirm that 119
they are hair-like or feather-like integumentary structures. The four types of filaments 120
described here show distinct distributions and morphologies. They are separated 121
clearly from the sedimentary matrix by sharp boundaries (Supplementary Fig. 4gi). 122
There is no evidence that one or more filament type(s) were generated taphonomically, 123
e.g. through selective degradation or fossilization, or superimposition of filaments. 124
For instance, although Type 1 and 4 filaments occur widely in both specimens, Type 4 125
occurs only in the wings, while Type 1 occupies the remaining body regions. Type 1 126
filaments are thus not degraded products of Type 4, and Type 4 filaments do not 127
represent superimposed clusters of Type 1 filaments. Filament types 2 and 3 occur 128
only in CAGS–Z070. Type 3 occurs only in the facial area and is associated with Type 129
1, where Types 2 and 4 are not evident. Type 3 filaments are thus not degraded Type 2 130
or 4 filaments. Central filaments of Type 3 are morphologically identical to the short, 131
distally tapering filaments of Type 1, but the branching filaments are much thinner (< 132
40 μm (Type 3) versus >70 μm (Type 1) wide) and shorter (< 0.6 mm vs. > 3.5 mm 133
7
long) than the latter. The branching filaments are thus unlikely to reflect 134
superimposition of clusters of Type 1 filaments. In contrast, the distal ends of Type 2 135
filaments are similar, and have a similar distribution pattern to, Type 1 filaments. An 136
alternative interpretation, that Type 2 filaments might represent superimposition of 137
Type 1 filaments at their proximal ends, is unlikely (see detailed discussion in 138
Supplementary text). 139
Feathers and feather-like integumentary structures have been reported in 140
non-avian dinosaurs, although debate continues about their true nature2. These 141
structures have been ascribed to several morphotypes, some absent in living birds3,5, 142
and provide a basis to analyse the evolutionary significance of pterosaur pycnofibres. 143
The pterosaur Type 1 filaments resemble monofilaments in the ornithischian 144
dinosaurs Tianyulong and Psittacosaurus and the coelurosaur Beipiaosaurus: 145
unbranched, cylindrical structures with a midline groove that widens towards the base 146
(presumed in Beipiaosaurus)3,5. The pterosaur Type 2 filaments resemble the 147
brush-like bundles of filaments in the coelurosaurs Epidexipteryx and Yi3,5,28: both 148
comprise parallel filaments that unite proximally. The morphology and circum-cranial 149
distribution of pterosaur Type 3 filaments resemble bristles in modern birds1, but 150
surprisingly do not correspond to any reported morphotype in non-avian dinosaurs. 151
The Type 3 filaments recall bilaterally branched filaments in Sinornithosaurus, 152
Anchiornis, and Dilong, but the latter filaments branch throughout their length rather 153
than halfway along the central filament(s), as in the pterosaur structure3,5. The 154
pterosaur Type 4 filaments are identical to the radially branched, downy feather-like 155
8
morphotype found widely in coelurosaurs such as Sinornithosaurus, Beipiaosaurus, 156
Protarchaeopteryx, Caudipteryx, and Dilong3,5. 157
The filamentous integumentary structures in our anurognathid pterosaurs are thus 158
remarkably similar to feathers and feather-like structures in non-avian dinosaurs. 159
Intriguingly, cylindrical (Type 1), radially symmetrical branched (Types 2 and 4) and 160
bilaterally symmetrical branched (Type 3) filaments clearly coexisted in individual 161
animals; these structures may represent transitional forms in the evolution of feathers, 162
as revealed by developmental studies3,5. 163
These new findings warrant revision of the origin of complex feather-like 164
branching integumentary structures from Dinosauria to Avemetatarsalia, the wider 165
clade that includes dinosaurs, pterosaurs, and close relatives4,29. The early 166
evolutionary history of bird feathers and homologous structures in dinosaurs, and the 167
multiple complex pycnofibres of pterosaurs, is enigmatic. A previous study concluded 168
that the common ancestor of these clades bore scales and not filamentous 169
integumentary appendages2, but this result emerged only when the filaments of 170
pterosaurs were coded as non-homologous with those of dinosaurs. There are no 171
morphological criteria, however, for such a determination. The presence of multiple 172
pycnofibre types and their morphological, ultrastructural and chemical similarity to 173
feathers and feather-like structures in various dinosaurian clades, confirms their likely 174
homology with filamentous structures in non-avian dinosaurs and birds. Comparative 175
phylogenetic analysis produces equivocal results: maximum likelihood modelling of 176
plausible ancestral states, against various combinations of branch length and character 177
9
transition models (Supplementary text and Supplementary Fig. 9, Table 3), reveals 178
various potential solutions. The statistically most likely result (Fig. 3 and 179
Supplementary Table 3, highest log-likelihood value) shows that the avemetatarsalian 180
ancestors of dinosaurs and pterosaurs possessed integumentary filaments, with highest 181
likelihood of possessing monofilaments; tufts of filaments, and, especially, brush-type 182
filaments, are less likely ancestral states. This confirms that feather-like structures 183
arose in the Early or Middle Triassic. The alternative tree for Dinosauria, with 184
Ornithischia and Theropoda paired as Ornithoscelida30, produces an identical result. 185
We present these modelling data with caution, however, for two reasons: (1) the 186
tree rooting method can influence the result (Supplementary Table 3), favouring 187
results in which either scales are the basal condition or where non-theropod 188
feather-like structures and feathers evolved independently (Supplementary Figure 9, 189
Table 3), and (2) there is no adequate way to model probabilities of evolution of all 190
six feather types, or to model probabilities of transitions between the six different 191
feather types. 192
The discovery of multiple types of feather-like structures in pterosaurs has broad 193
implications for our understanding of pterosaur biology and the functional origin of 194
feather-like structures in Avemetatarsalia31,32. Potential functions of these structures 195
include insulation, tactile sensing, streamlining and coloration (primarily for 196
camouflage and signalling), as for bristles, down feathers and mammalian hairs31-34. 197
Type 1, 2 and 4 filaments could shape a filamentous covering around the body and 198
wings (Fig. 4) that might have functioned in streamlining the body surface in order to 199
10
reduce drag during flight, as for modern bat fur or avian covert feathers33,35. Type 1 200
and 2 filaments occur in considerably high densities, particularly around the neck, 201
shoulder, hindlimb and tail regions where the high degree of superposition prevents 202
easy discrimination of adjacent fibres. This, along with the wide distribution and 203
frayed appearance, resembles mammalian underfur adapted for thermal insulation36,35. 204
Despite the less dense packing of Type 4 filaments on the wings, the morphology of 205
the structures is consistent with a thermoregulatory function: down feathers can 206
achieve similar insulation as mammalian hair with only about half the mass, due to 207
their air-trapping properties and high mechanical resilience, effective in retaining an 208
insulating layer of still air38. This may optimize the encumbrance of the large wing 209
area to wing locomotion18. Type 3 filaments around the jaw (Fig. 4) may have had 210
tactile functions in e.g. prey handling, information gathering during flight, navigating 211
in nest cavities and on the ground at night, similar to bristles in birds39. 212
213
References 214
1 Lucas, A. M. S. & Peter, R. Avian anatomy: integument (U.S. Agricultural 215
Research Service, Washington, 1972). 216
2 Barrett, P. M., Evans, D. C. & Campione, N. E. Evolution of dinosaur epidermal 217
structures. Biol. Lett. 11, 20150229 (2015). 218
3 Xu, X. et al. An integrative approach to understanding bird origins. Science 346, 219
1253293 (2014). 220
4 Di-Poï, N. & Milinkovitch, M. C. The anatomical placode in reptile scale 221
11
morphogenesis indicates shared ancestry among skin appendages in amniotes. Sci. 222
Adv. 2, e1600708 (2016). 223
5 Chen, C. F. et al. Development, regeneration, and evolution of feathers. Ann. Rev. 224
Anim. Biosci. 3, 169–195 (2015). 225
6 Mayr, G., Pittman, M., Saitta, E., Kaye, T. G. & Vinther, J. Structure and 226
homology of Psittacosaurus tail bristles. Palaeontol. 59, 793–802 (2016). 227
7 Zheng, X. T., You, H. L., Xu, X. & Dong, Z. M. An Early Cretaceous 228
heterodontosaurid dinosaur with filamentous integumentary structures. Nature 229
458, 333–336 (2009). 230
8 Godefroit, P. et al. A Jurassic ornithischian dinosaur from Siberia with both 231
feathers and scales. Science 345, 451–455 (2014). 232
9 Kellner, A. W. et al. The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, 233
Batrachognathinae) and the structure of the pterosaur wing membrane. Proc. Biol. 234
Sci. 277, 321–329 (2010). 235
10 Sharov, A. G. New flying reptiles from the Mesozoic of Kazakhstan and Kirgizia 236
(in Russian). Akad. nauk SSSR Paleont. Inst. Tr. 130, 104–113 (1971). 237
11 Czerkas, S. A. & Ji, Q. A new rhamphorhynchoid with a headcrest and complex 238
integumentary structures. In: S. J. CZERKAS (Ed), Feathered dinosaurs and the 239
origin of flight (Blanding, The Dinosaur Museum), 15–41 (2002). 240
12 Unwin, D. M. & Bakhurina, N. N. Sordes pilosus and the nature of the pterosaur 241
flight apparatus. Nature 371, 62–64 (1994). 242
13 Ji, Q. & Yuan, C. Discovery of two kinds of protofeathered pterosaurs in the 243
12
Mesozoic Daohugou Biota in the Ningcheng region and its stratigraphic and 244
biologic significances. Geol. Rev. 48, 221–224 (2002). 245
14 Xu, X., Zhou, Z., Sullivan, C., Wang, Y. & Ren, D. An updated review of the 246
MiddleLate Jurassic Yanliao Biota: chronology, taphonomy, paleontology and 247
paleoecology. Acta Geol. Sin. (Engl. Ed.) 90, 2229–2243 (2016). 248
15 Wang, X. et al. Basal paravian functional anatomy illuminated by high-detail 249
body outline. Nat. Commun. 8, (2017). 250
16 Kaye, T. G. et al. Laser-stimulated fluorescence in paleontology. PloS one 10, 251
e0125923 (2015). 252
17 Unwin, D. M. On the phylogeny and evolutionary history of pterosaurs. Geol. 253
Soc., London, Spec. Publ. 217, 139–190 (2003). 254
18 Frey, E., Tischlinger, H., Buchy, M. C., & Martill, D. M. New specimens of 255
Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy 256
and locomotion. Geol. Soc., London, Spec. Publ. 217, 233–266 (2003). 257
19 Lindgren, J. et al. Interpreting melanin-based coloration through deep time: a 258
critical review. Proc. R. Soc. B 282, 20150614 (2015). 259
20 Lindgren, J. et al. Molecular composition and ultrastructure of Jurassic paravian 260
feathers. Sci. Rep. 5, 13520 (2015). 261
21 Barden, H. E. et al. Morphological and geochemical evidence of eumelanin 262
preservation in the feathers of the Early Cretaceous bird, Gansus yumenensis. 263
PLoS One 6, e25494 (2011). 264
22 Bendit, E. Infrared absorption spectrum of keratin. I. Spectra of α-, β-, and 265
13
supercontracted keratin. Biopolymers 4, 539–559 (1966). 266
23 Martinez-Hernandez, A. L., Velasco-Santos, C., De Icaza, M. & Castano, V. M. 267
Microstructural characterisation of keratin fibres from chicken feathers. Int. J. 268
Envir. Pollut. 23, 162–178 (2005). 269
24 Liu, Y. et al. Comparison of structural and chemical properties of black and red 270
human hair melanosomes. Photochem. Photobiol. 81, 135–144 (2005). 271
25 Alibardi, L. Adaptation to the land: the skin of reptiles in comparison to that of 272
amphibians and endotherm amniotes. J. Exp. Zool. 298B, 12–41 (2009). 273
26 Kreplak, L., Doucet, J., Dumas, P. & Briki, F. New aspects of the α-helix to 274
β-sheet transition in stretched hard α-keratin fibers. Biophys. J. 87, 640–647 275
(2004). 276
27 Yassine, W., Taib, N., Federman, S., Milochau, A., Castano, S., Sbi, W. Manigand, 277
C., Laguerre, M., Desbat, B., Oda, R. & Lang, J. Reversible transition between 278
α-helix and β-sheet conformation of a transmembrane domain. Biochim. Biophys. 279
Acta – Biomembranes. 1788, 1722–1730 (2009). 280
28 Xu, X. et al. A bizarre Jurassic maniraptoran theropod with preserved evidence of 281
membranous wings. Nature 521, 70–73 (2015). 282
29 Donoghue, P. C. J. & Benton, M. J. Rocks and clocks: calibrating the Tree of Life 283
using fossils and molecules. Trends Ecol. Evol. 22, 424–431 (2007). 284
30 Baron, M. G., Norman, D. B. & Barrett, P. M. A new hypothesis of dinosaur 285
relationships and early dinosaur evolution. Nature 543, 501–506 (2017). 286
31 Persons IV, W. S. & Currie, P. J. Bristles before down: a new perspective on the 287
14
functional origin of feathers. Evolution 69, 857–862 (2015). 288
32 Ruxton, G. D., Persons IV, W. S. & Currie, P. J. A continued role for signaling 289
functions in the early evolution of feathers. Evolution 71, 797–799 (2017). 290
33 Bullen, R. D. & McKenzie, N. L. The pelage of bats (Chiroptera) and the 291
presence of aerodynamic riblets: the effect on aerodynamic cleanliness. Zoology 292
111, 279–286 (2008). 293
34 Caro, T. The adaptive significance of coloration in mammals. BioScience 55, 294
125–136 (2005). 295
35 Homberger, D. G., & de Silva, K. N. Functional microanatomy of the 296
feather-bearing integument: implications for the evolution of birds and avian 297
flight. Amer. Zool. 40, 553–574 (2000). 298
36 Scholander, P., Walters, V., Hock, R. & Irving, L. Body insulation of some arctic 299
and tropical mammals and birds. Biol. Bull. 99, 225–236 (1950). 300
37 Ling, J. K. Pelage and molting in wild mammals with special reference to aquatic 301
forms. Quart. Rev. Biol. 45, 16–54 (1970). 302
38 Gao, J., Yu, W. & Pan, N. Structures and properties of the goose down as a 303
material for thermal insulation. Text. Res. J. 77, 617–626 (2007). 304
39 Cunningham, S. J., Alley, M. R., & Castro, I. Facial bristle feather histology and 305
morphology in New Zealand birds: implications for function. J. Morphol. 272, 306
118–128 (2011). 307
308
Supplementary Information is available in the online version of the paper. 309
15
310
Acknowledgements We thank Qiang Ji, Shu’an Ji and Hao Huang for access to the 311
specimen CAGS–Z070, as well as Simon C. Kohn, Yan Fang, Chunzhao Wang and 312
Tong He for laboratory assistance. This work was supported by the National Science 313
Foundation of China (41672010; 41688103) and the Strategic Priority Research 314
Program (B) of the Chinese Academy of Sciences (XDB26000000) to B.Y.J., the 315
Research Grant Council of Hong Kong-General Research Fund (17103315) to M.P., 316
ERC-StG-2014-637691-ANICOLEVO to M.E.M., and Natural Environment 317
Research Council Standard Grant NE/1027630/1 to M.J.B. 318
319
Author Contributions B.Y.J. and M.J.B. designed the research, Z.X.Y., B.Y.J. and 320
X.X. systematically studied the specimens, Z.X.Y., S.L.K., M.E.M, and P.J.O. did the 321
SEM analysis, Z.X.Y. and B.Y.J. did the FTIR analysis, M.P. and T.G.K. did the LSF 322
imaging, data reduction and interpretation, M.J.B. did the maximum likelihood 323
analyses, and Z.X.Y., B.Y.J., M.J.B., M.E.M, X.X. and P.J.O. wrote the paper; all 324
authors approved the final draft of the paper. 325
326
Author Information Reprints and permissions information is available at 327
www.nature.com/reprints. The authors declare no competing financial interests. 328
Correspondence and requests for materials should be addressed to B.Y.J. 329
(byjiang@nju.edu.cn) or M.J.B. (mike.benton@bristol.ac.uk). 330
331
16
332
Figure 1 | Integumentary filamentous structures in CAGSZ070. a, Overview 333
shows extensive preservation of soft tissues. bp, Details of the integumentary 334
filaments in the regions indicated in a on the head and neck (bd, ij), forelimb (fg), 335
wing (lm) and tail (op), and illustrated reconstructions of the filaments (e: Type 1 336
filament; h: Type 2 filament; k: Type 3 filament; n: Type 4 filament). Scale bars: 20 337
mm in a; 10 mm in b; 500 µm in c and i; 100 µm in d; 1 mm in f, l, m and p; 200 µm 338
in g and j; 5 mm in o. 339
340
Figure 2 | Preservation, microstructure and chemistry of the integumentary 341
filamentous structures in NJU–57003. a, Laser-stimulated fluorescence6,15,16 image 342
highlights extensive preservation of soft tissues (black areas). b–f, Details of the 343
integumentary filaments in the regions indicated in A on the head and neck (b–c), 344
wing (d–e) and tail (f). g–h, Scanning electron micrographs of the monofilaments on 345
the neck and hindlimb of NJU57003 (samples 10 and 39, respectively, 346
Supplementary Fig. 1a) show densely packed, elongate and oblate melanosomes. i, 347
FTIR absorbance spectra of the monofilaments, monofilaments with sediment matrix, 348
and sediment matrix in NJU57003 (Sample 15, Supplementary Fig. 1a) compared 349
with spectra from a feather of Anchiornis (from ref. 20), extant Marabou stork feather 350
(from ref. 21) and black and red human hair melanosomes (from ref. 24). Scale bars: 20 351
mm in a; 1 mm in b, c and e; 5 mm in d and f; 1 μm in g and h. 352
17
Figure 3 | Phylogenetic comparative analysis of integumentary filament and 353
feather evolution in pterosaurs and archosaurs. The phylogeny is scaled to 354
geological time, with recorded terminal character states for each species, and 355
estimated ancestral character states at the lower nodes. The model is the most likely of 356
the maximum likelihood models, based on minimum-branch lengths (mbl) and 357
transitions occurring as all-rates-different (ARD), but other results with lower 358
likelihoods show scales as ancestral. The ancestral state reconstruction shows a 359
combination of monofilaments, tuft-like filaments, and brush-type filaments as the 360
ancestral state for Avemetatarsalia and for Dinosauria. The estimated ancestral state 361
for Theropoda comprises all five feather states. Numbered small vertical arrows 362
indicate earliest occurrences of feather types 2–6. Two hypotheses for timing of avian 363
feather origins are indicated: A, early origin, at the base of Avemetatarsalia in the 364
Early Triassic, or B, late origin, at the base of Maniraptora in the Early–Middle 365
Jurassic. 366
367
Figure 4 | Reconstruction of one of the studied anurognathid pterosaurs, 368
exhibiting diverse types of pycnofibres distributed in different body parts. 369
Scales
Monofilaments
Brush-like filaments
Tufts of filaments
Open pennaceous feathers (no secondary branching)
Closed pennaceous feathers (with secondary branching)
THEROPODA
SAUROPODOMORPHA
ORNITHISCHIA
PTEROSAURIA
AVES
MANIRAPTORA
Sordes pilosus
Yanliao anurognathid
Jeholopterus ningchengensis
Tianyulong confuciusi
Scelidosaurus harrisoniiGigantspinosaurus sichuanensis
Hesperosaurus mjosi
cf Stegosaurus sp. Liaoningosaurus paradoxus Tarchia kielanae
Euoplocephalus tutus
Dyoplosaurus acutosquameus
Scolosaurus cutleri
Kulindadromeus zabaikalicus Psittacosaurus sp. Centrosaurus apertus
Chasmosaurus belli
Triceratops horridus
Tenontosaurus sp.
Mantellisaurus atherfieldensis Parasaurolophus walkeri
Hypacrosaurus altispinus
Magnipaulia laticaudus
Corythosaurus casuarius
Corythosaurus intermedius
Lambeosaurus clavinitialis
Lambeosaurus magnicristatus
Brachylophosaurus canadensis
Maiasaura peeblesorum
Edmontosaurus annectens
Edmontosaurus regalis
Gryposaurus monumentensis
Gryposaurus notabilis
Prosaurolophus maximus
Saurolophus angustirostris
Saurolophus osborni
Tehuelchesaurus benitezii
Mamenchisaurus youngi
Barosaurus lentus
Diplodocus sp.
Camarasaurus sp. Auca Maheuvo titanosaur
Pelorosaurus becklesii Carnotaurus sastrei
Sciurumimus albersodoefri
Allosaurus fragilis Concavenator corcovatus
Dilong paradoxus
Yutyrannus huali Tarbosaurus bataar
Tyrannosaurus rex
Sinocalliopteryx gigas
Compsognathus longipes
Juravenator starkiiSinosauropteryx prima Ornithomimus edmontonicus
Shuvuuia deserti
Beipiaosaurus inexpectus
Similicaudipteryx yixianensis
Protarchaeopteryx robusta
Caudipteryx dongi
Caudipteryx zoui
Pedopenna daohugouensis
Epidexipteryx hui
Scansoriopteryx heilmanni
Eosinopteryx brevipenna Velociraptor mongoliensis
Sinornithosaurus millenii
Microraptor gui
Microraptor zhaoianus
Jinfengopteryx elegans
Aurornis xui
Anchiornis huxleyi
Archaeopteryx lithographica
Xiaotingia zhengi Confuciusornis sanctus Rahonavis ostromi
DINOSAURIA
AVEMETATARSALIA
COELUROSAURIA
SAURISCHIA
6
5
4
4
4
3
3
2
2
2
1
1
PSEUDOSUCHIA (’crocodile-line archosaurs’)
A B
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250 Induan
Olenekian
Anisian
Ladinian
Carnian
Norian
Rhaetian
Hettangian
Sinemurian
Pliensbachian
Toarcian
Aalenian
Bajocian
Bathonian
Callovian
Oxfordian
Kimmeridgian
Tithonian
Berriasian
Valanginian
Hauterivian
Barremian
Aptian
Albian
Cenomanian
Turonian
Coniacian
Santonian
Campanian
Maastrichtian
Danian
Selandian
Thanetian
Ypresian
Lutetian
Bartonian
Priabonian
Rupelian
Chattian
Lower
Middle
Upper
Lower
Middle
Upper
Lower
Upper
Paleocene
Eocene
Oligocene
Triassic Jurassic Cretaceous Paleogene
early origin of feathers late origin of feathers
1
2
3
4
5
6
2,3
4
5
6
... As a result, feathers have long been regarded as the key innovation responsible for the emergence of flight capability in, and adaptive radiations of, birds 1,2 . Fossilised feathers and feather-like filamentous integumentary structures, however, have been reported in other groups, including non-avian theropods, ornithischians and pterosaurs [2][3][4] . Subsequently the term feather has been equivocal in the literature, referring to (1) structures comparable to modern feathers (e.g. ...
... Despite decades of research, the evolutionary origins of feathers remain poorly resolved and, as a result, are the subject of ongoing debate. Certain studies favour independent evolution of feathers in theropods, ornithischians and pterosaurs 8,9 , but given the shared morphology and histology of the feather structures, and the likely shared genomic heritage and shared pattern of developmental stages of these organisms, we consider a single point of origin more likely [2][3][4]10 . At the very least, the available fossil and developmental evidence strongly suggests that very similar, if not identical, genetic and developmental processes underpin the production of feathers in different archosaurian groups 2,11,12 , regardless of whether a single origin applies. ...
... Vertical sections of the fossil skin show two major layers (Figs. [3][4][5]. The upper layer is ca. 25 Fig. 4d). ...
Article
Full-text available
Fossil feathers have transformed our understanding of integumentary evolution in vertebrates. The evolution of feathers is associated with novel skin ultrastructures, but the fossil record of these changes is poor and thus the critical transition from scaled to feathered skin is poorly understood. Here we shed light on this issue using preserved skin in the non-avian feathered dinosaur Psittacosaurus. Skin in the non-feathered, scaled torso is three-dimensionally replicated in silica and preserves epidermal layers, corneocytes and melanosomes. The morphology of the preserved stratum corneum is consistent with an original composition rich in corneous beta proteins, rather than (alpha-) keratins as in the feathered skin of birds. The stratum corneum is relatively thin in the ventral torso compared to extant quadrupedal reptiles, reflecting a reduced demand for mechanical protection in an elevated bipedal stance. The distribution of the melanosomes in the fossil skin is consistent with melanin-based colouration in extant crocodilians. Collectively, the fossil evidence supports partitioning of skin development in Psittacosaurus: a reptile-type condition in non-feathered regions and an avian-like condition in feathered regions. Retention of reptile-type skin in non-feathered regions would have ensured essential skin functions during the early, experimental stages of feather evolution.
... Nevertheless, proteinaceous components that might be from keratins have been detected in several fossils by FTIR spectra (e.g. (31,38,39)). Amide I and II bands were detected in a mummified skin from an Upper Cretaceous hadrosaur dinosaur (31). ...
... Amide I, II, and III absorption bands, along with the C-H peaks, were present in the full spectrum from an Eocene aged fossil reptile skin, and FTIR mapping further supported the endogenous origin of the proteinaceous components within the fossilized soft tissue (38). The oldest record is from carbonaceous filaments of a mid-Late Jurassic pterosaur, with the presence of the amide I and II bands in the FTIR record (39), which is much older than our Cretaceous feathers. Their studied materials show weaker melanin signals than the fossil feathers in this study, which contain abundant melanosomes. ...
Article
Full-text available
Exceptionally preserved feathers from the Mesozoic era have provided valuable insights into the early evolution of feathers and enabled colour reconstruction of extinct dinosaurs, including early birds. Mounting chemical evidence for the two key components of feathers–keratins and melanins - in fossil feathers has demonstrated that exceptional preservation can be traced down to the molecular level. However, the chemical changes that keratin and eumelanin undergo during fossilization are still not fully understood, introducing uncertainty in the identification of these two molecules in fossil feathers. To address this issue, we need to examine their taphonomic process. In this study, we analyzed the structural and chemical composition of fossil feathers from the Jehol Biota and compared them with the structural and chemical changes observed in modern feathers during the process of biodegradation and thermal degradation, as well as the structural and chemical characteristics of a Cenozoic fossil feather. Our results suggest that the taphonomic process of feathers from the Cretaceous Jehol Biota is mainly controlled by the process of thermal degradation. The Cretaceous fossil feathers studied exhibited minimal keratin preservation but retained strong melanin signals, attributed to melanin’s higher thermal stability. Low-maturity carbonaceous fossils can indeed preserve biosignals, especially signals from molecules with high resistance to thermal degradation. These findings provide new clues about the preservation potential of keratin and melanin, and serve as a reference for searching for those two biomolecules in different geological periods and environments.
... Há proposta de que possuíam protopenas como os dinossauros (Ji & Yuan, 2002, Czerkas & Ji, 2002. Em abordagens seguintes, alguns referiram--se a esses elementos pelo nome picnofibras (Kellner et al., 2010), que seriam homólogos às penas, incluindo a presença de melanossomos -organelas que armazenam melanina -nelas presentes (Yang et al., 2019). Por outro lado, a proposta não foi amplamente aceita, havendo críticas a respeito da interpretação errônea de parte dessas estruturas e/ ou mesmo traços de substâncias orgânicas nas pic-nofibras , Yang et al., 2020. ...
Article
Full-text available
Introdução. A Paleontologia integra conceitos de outras áreas das Ciências da Natureza para tratar da evolução e mudanças ambientais no tempo Geológico. A despeito da sua importância, o rico registro fossilífero brasileiro é raramente tratado em sala de aula. Objetivos. Este trabalho propõe o jogo de tabuleiro “Qual é o Pterossauro?” como ferramenta adicional para o ensino de Paleontologia no Ensino Básico. Metodologia. As regras e as ilustrações são autorais e inéditas, e se basearam na literatura científica. Após a exposição ao tema em formato de uma aula, o jogo foi aplicado com alunos e posteriormente avaliado por formulário. Resultados. O jogo foi considerado como boa experiência educativa por 92 crianças de duas escolas públicas da Zona Leste da Cidade de São Paulo. Conclusão. A originalidade do jogo e de todas as ilustrações que incluem representações de pterossauros brasileiros se destacam por se tratarem de material original e autoral. O jogo se demonstrou viável para apresentar conceitos de Paleontologia e pterossauros brasileiros, como ferramenta para o ensino de Geociências no Ensino Básico e valorização do patrimônio fossilífero do nosso país.
... They preserve millimeter-sized, fiber-like epidermal structures (pycnofibers) on the head (except on the jaws), neck, body, and the proximal portions of the limbs (Frey & Martill, 1998;Wang et al., 2002). More recently, Yang et al. (2019) and Cincotta et al. (2022) reported the presence in various pterosaurs of branched feather-like structures that resemble the feathers in non-avian theropod dinosaurs. The latter authors also observed the presence of melanosomes in these feather-like structures, indicating that they were colored in life. ...
... There are at least two other quite distinctive palate configurations present in non-pterodactyloids. The most extreme, as has been already pointed out before, is found in anurognathids where most elements are reduced to rodlike structures 32,50,[52][53][54] . The other distinctive palate has been reported in the wukongopterid Kunpengopterus with different relation of the palatal openings, particularly the huge size of the postpalatine fenestra 41 . ...
Article
Full-text available
Among the least studied portion of the pterosaur skeleton is the palate, which tends to be poorly preserved and commonly only visible from one side (the ventral portion). Even in well-preserved specimens, the bones tend to be fused, with the limits of individual palatal elements obscured. To shed new light on this region, we employed advanced X-ray imaging techniques on the non-pterodactyloid Kunpengopterus (Wukongopteridae), and the pterodactyloids Dsungaripterus (Dsungaripteridae), Hongshanopterus (Istiodactylidae), and Hamipterus (Hamipteridae). Our analyses revealed the presence of sutures between palatal bones in Dsungaripterus and Kunpengopterus, which resulted in different interpretations of the relation between palatine, ectopterygoid, and pterygoid, leading to a new identification of the palatal openings. Furthermore, our study shows six main observations such as the variation of the angle between the palatine rami and the variation in the relative sizes of the palatal openings. We also point out that the presence of a maxillopalatine fenestra (previously identified as postpalatine fenestra), is unique within Diapsida. Although much more work needs to be done, we showed that advanced X-ray imaging techniques open a window for understanding pterosaur cranial anatomy and provide a new perspective for investigating the evolutionary history of these flying reptiles.
Preprint
Full-text available
Feathers are a key novelty underpinning the evolutionary success of birds, yet the origin of feathers remains poorly understood. Debates about feather evolution hinge upon whether filamentous integument has evolved once or multiple time independently on the lineage leading to modern birds. These contradictory results stem from subjective methodological differences in statistical ancestral state estimates. Here we conduct a comprehensive comparison of ancestral state estimation methodologies applied to stem-group birds, testing the role of outgroup inclusion, tree time scaling method, model choice and character coding strategy. Models are compared based on their Akaike Information Criteria (AIC), mutual information, as well as the uncertainty of marginal ancestral state estimates. Our results demonstrate that ancestral state estimates of stem-bird integument are strongly influenced by tree time scaling method, outgroup selection and model choice, while character coding strategy seems to have less effect on the ancestral estimates produced. We identify the best fitting models using AIC scores and a leave-one-out cross-validation approach (LOOCV). Our analyses broadly support the independent origin of filamentous integument in dinosaurs and pterosaurs and support a younger evolutionary origin of feathers than has been suggested previously. More generally, our study highlights that special care must be taken in selecting the outgroup, tree and model when conducting ASE analyses. With respect to model selection, our results suggest that considering a LOOCV approach, may yield more reliable results than simply comparing AIC scores when the analyses involve a limited number of taxa.
Article
Pterosaurs are powered flight vertebrates that first emerged in the Late Triassic and persisted until the end of the Cretaceous. Recent studies on the ecological niches and habitats of pterosaurs, based on discoveries of Cretaceous bone beds in China, Brazil, Morocco, and other locations, suggest a decline in pterosaur diversity during the mid-Cretaceous. Various hypotheses have been proposed to interpret this phenomenon. This study focuses on newly discovered pterosaur tracks at the Upper Cretaceous (Truonian) Hwasun Seoyuri tracksite in Korea. The analysis is based on pterosaur tracks from in situ and ex situ specimens that originate from a variety of stratigraphic levels. The evidence found suggests that the Hwasun Seoyuri tracksite was occupied by small pterosaurs over an extended period, with indications of recurrent activity across at least six levels. Furthermore, the footprint sizes observed across these multiple layers follow a non-skewed normal distribution. Considering the known logarithmic growth characteristics of pterosaurs, this result suggests a predominantly immature population at this site. The prevalence of mid-Cretaceous non-marine pterosaur tracksites on the Korean Peninsula may reflect broader ecological shifts for pterosaurs during this period. This evidence is considered alongside the habitat shifts suggested by other non-marine pterosaur fossil sites in China and Brazil, as well as with indications of the decline in Late Cretaceous non-marine basins.
Article
Full-text available
Body shape is a fundamental expression of organismal biology, but its quantitative reconstruction in fossil vertebrates is rare. Due to the absence of fossilized soft tissue evidence, the functional consequences of basal paravian body shape and its implications for the origins of avians and flight are not yet fully understood. Here we reconstruct the quantitative body outline of a fossil paravian Anchiornis based on high-definition images of soft tissues revealed by laser-stimulated fluorescence. This body outline confirms patagia-bearing arms, drumstick-shaped legs and a slender tail, features that were probably widespread among paravians. Finely preserved details also reveal similarities in propatagial and footpad form between basal paravians and modern birds, extending their record to the Late Jurassic. The body outline and soft tissue details suggest significant functional decoupling between the legs and tail in at least some basal paravians. The number of seemingly modern propatagial traits hint that feathering was a significant factor in how basal paravians utilized arm, leg and tail function for aerodynamic benefit.
Article
Full-text available
The northeastern Chinese Yanliao Biota (sometimes called the Daohugou Biota) comprises numerous, frequently spectacular fossils of non-marine organisms, occurring in Middle-Upper Jurassic strata in western Liaoning, northern Hebei, and southeastern Inner Mongolia. The biota lasted for about 10 million years, divided into two phases: the Bathonian-Callovian Daohugou phase (about 168–164 million years ago) and the Oxfordian Linglongta phase (164–159 million years ago). The Yanliao fossils are often taphonomically exceptional (many vertebrate skeletons, for example, are complete and accompanied by preserved integumentary features), and not only are taxonomically diverse but also include the oldest known representatives of many groups of plants, invertebrates, and vertebrates. These fossils have provided significant new information regarding the origins and early evolution of such clades as fleas, birds, and mammals, in addition to the evolution of some major biological structures such as feathers, and have demonstrated the existence of a complex terrestrial ecosystem in northeast China around the time of the Middle-Late Jurassic boundary.
Article
Full-text available
We examined bristle-like appendages on the tail of the Early Cretaceous basal ceratopsian dinosaur Psitta-cosaurus with laser-stimulated fluorescence imaging. Our study reveals previously unknown details of these structures and confirms their identification as integumentary appendages. For the first time, we show that most bristles appear to be arranged in bundles and that they exhibit a pulp that widens towards the bristle base. We consider it likely that the psittacosaur bristles are structurally and developmentally homologous to similar filamentous appendages of other dinosaurs, namely the basal heterodontosaurid Tianyulong and the basal therizinosauroid theropod Beipiaosaurus, and attribute the greater robustness of the bristles of Psitta-cosaurus to a higher degree of cornification and calcification of its integument (both skin and bristles). Although the psittacosaur bristles are probably homologous with avian feathers in their origin from discrete cell populations, it is uncertain whether they developed from a follicle, one of the developmental hallmarks of true feathers. In particular, we note a striking resemblance between the psittacosaur bristles and the cornified spine on the head of the horned screamer, Anhima cornuta, an extant anseriform bird. Similar , albeit thinner keratinous filaments of extant birds are the 'beard' of the turkey, Meleagris gallopavo, and the crown of the Congo peafowl, Afropavo congensis. All of these structures of extant birds are distinct from true feathers, and because at least the turkey beard does not develop from follicles, detailed future studies of their development would be invaluable towards deepening our understanding of dinosaur filamentous integumentary structures.
Article
Full-text available
Most mammals, birds, and reptiles are readily recognized by their hairs, feathers, and scales, respectively. However, the lack of fossil intermediate forms between scales and hairs and substantial differences in their morphogenesis and protein composition have fueled the controversy pertaining to their potential common ancestry for decades. Central to this debate is the apparent lack of an “anatomical placode” (that is, a local epidermal thickening characteristic of feathers’ and hairs’ early morphogenesis) in reptile scale development. Hence, scenarios have been proposed for the independent development of the anatomical placode in birds and mammals and parallel co-option of similar signaling pathways for their morphogenesis. Using histological and molecular techniques on developmental series of crocodiles and snakes, as well as of unique wild-type and EDA (ectodysplasin A)–deficient scaleless mutant lizards, we show for the first time that reptiles, including crocodiles and squamates, develop all the characteristics of an anatomical placode: columnar cells with reduced proliferation rate, as well as canonical spatial expression of placode and underlying dermal molecular markers. These results reveal a new evolutionary scenario where hairs, feathers, and scales of extant species are homologous structures inherited, with modification, from their shared reptilian ancestor’s skin appendages already characterized by an anatomical placode and associated signaling molecules.
Book
Introduction.- First Steps in R for Phylogeneticists.- Phylogenetic Data in R.- Plotting Phylogenies.- Phylogeny Estimation.- Analysis of Macroevolution with Phylogenies.- Developing and Implementing Phylogenetic Methods in R.
Article
For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.
Article
Persons and Currie (2015) argued against either flight, thermoregulation, or signalling as a functional benefit driving the earliest evolution of feathers; rather, they favoured simple feathers having an initial tactile sensory function, which changed to a thermoregulatory function as density increased. Here, we explore the relative merits of early simple feathers that may have originated as tactile sensors progressing instead towards a signalling, rather than (or in addition to), a thermoregulatory function. We suggest that signalling could act in concert with a sensory function more naturally than could thermoregulation. As such, the dismissal of a possible signalling function and the presumption that an initial sensory function led directly to a thermoregulatory function (implicit in the title "bristles before down") are premature. This article is protected by copyright. All rights reserved.