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A Feathered Dinosaur Tail with Primitive Plumage
Trapped in Mid-Cretaceous Amber
dThe ﬁrst non-avialan theropod fragments preserved in amber
dVertebral outlines, curvature, and plumage suggest a source
dBranching structure in the feathers supports a barbule-ﬁrst
dIron within carbonized soft tissue suggests traces of original
material are present
Lida Xing, Ryan C. McKellar,
Xing Xu, ..., Kuowei Tseng, Hao Ran,
Philip J. Currie
Xing et al. describe the tail of a non-
avialan theropod (coelurosaur) preserved
in Burmese amber, combining bone
outlines with microscopic details of
plumage and integument. This specimen
sheds new light on the appearance and
evolution of plumage of dinosaurs,
providing a direct association between
amber-entombed plumage and body
Xing et al., 2016, Current Biology 26, 3352–3360
December 19, 2016 ª2016 Elsevier Ltd.
A Feathered Dinosaur Tail with Primitive Plumage
Trapped in Mid-Cretaceous Amber
*Ryan C. McKellar,
W. Scott Persons IV,
Michael J. Benton,
Alexander P. Wolfe,
and Philip J. Currie
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China
School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
Royal Saskatchewan Museum, Regina, Saskatchewan S4P 4W7, Canada
Biology Department, University of Regina, Regina, Saskatchewan S4S 0A2, Canada
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy
of Sciences, Beijing 100044, China
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Science, Beijing 100049, China
Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China
Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
Department of Exercise and Health Science, University of Taipei, Taipei 11153, China
Department of Geology, Chinese Culture University, Taipei 11114, China
Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection, Ministry of Education, Guilin 541004, China
*Correspondence: firstname.lastname@example.org (L.X.), email@example.com (R.C.M.)
In the two decades since the discovery of feathered
dinosaurs [1–3], the range of plumage known
from non-avialan theropods has expanded signiﬁ-
cantly, conﬁrming several features predicted by
developmentally informed models of feather evolu-
tion [4–10]. However, three-dimensional feather
morphology and evolutionary patterns remain difﬁ-
cult to interpret, due to compression in sedimen-
tary rocks [9, 11]. Recent discoveries in Cretaceous
amber from Canada, France, Japan, Lebanon,
Myanmar, and the United States [12–18] reveal
much ﬁner levels of structural detail, but taxonomic
placement is uncertain because plumage is rarely
associated with identiﬁable skeletal material .
Here we describe the feathered tail of a non-avialan
theropod preserved in mid-Cretaceous (99 Ma)
amber from Kachin State, Myanmar , with
plumage structure that directly informs the evolu-
tionary developmental pathway of feathers. This
specimen provides an opportunity to document pris-
tine feathers in direct association with a putative
juvenile coelurosaur, preserving ﬁne morphological
details, including the spatial arrangement of follicles
and feathers on the body, and micrometer-scale fea-
tures of the plumage. Many feathers exhibit a short,
slender rachis with alternating barbs and a uniform
series of contiguous barbules, supporting the devel-
opmental hypothesis that barbs already possessed
barbules when they fused to form the rachis .
Beneath the feathers, carbonized soft tissues offer
a glimpse of preservational potential and history for
the inclusion; abundant Fe
suggests that vestiges
of primary hemoglobin and ferritin remain trapped
within the tail. The new ﬁnding highlights the unique
preservation potential of amber for understanding
the morphology and evolution of coelurosaurian
RESULTS AND DISCUSSION
The tail within DIP-V-15103 is visible to the naked eye as an elon-
gate and gently curved structure (length = 36.73 mm). A dense
covering of feathers protrudes from the tail, obscuring underlying
details, so Synchrotron Radiation (SR) X-ray phase-contrast
mCT scanning was employed to examine concealed osteological
and soft tissue features (Figure 1). Soft tissues—presumably
muscles, ligaments, and skin—are visible sporadically through
the plumage, clinging to the bones in a manner suggestive
of the desiccation common to other vertebrate remains in
amber . These tissues have largely been reduced to a carbon
ﬁlm, retaining only traces of their original chemical composition.
Based on analyses further described in the Supplemental Infor-
mation,SRm-XFI shows that iron is present in the carbonized
soft tissues and as a series of ﬁne linear features corresponding
to exposed plumage (Figure 2). Copper is slightly more abundant
in amber containing plumage, but this signal is cryptic and not a
clear indicator for preserved pigments. Elements such as Ca, Sc,
Zn, Ti, Ge, and Mn appear to be associated with clay minerals
ﬁlling voids in the amber. We derived the valence state of iron
in the sample qualitatively by comparison to the standard XAS
of Fe foil, Fe
, and FeO. Our calculations indicate
that more than 80% of iron in the sample is ferrous (Fe
measurements have been made on vessels preserved within
3352 Current Biology 26, 3352–3360, December 19, 2016 ª2016 Elsevier Ltd.
Figure 1. Photomicrographs and SR X-Ray mCT Reconstructions of DIP-V-15103
(A) Dorsolateral overview.
(B) Ventrolateral overview with decay products (bubbles in foreground, staining to lower right).
(C) Caudal exposure of tail showing darker dorsal plumage (top), milky amber, and exposed carbon ﬁlm around vertebrae (center).
(D–H) Reconstructions focusing on dorsolateral, detailed dorsal, ventrolateral, detailed ventral, and detailed lateral aspects of tail, respectively.
(legend continued on next page)
Current Biology 26, 3352–3360, December 19, 2016 3353
Tyrannosaurus and Brachylophosaurus bones and have been in-
terpreted as indicating the presence of goethite and biogenic
iron oxides produced from hemoglobin decomposition .
The presence of large quantities of Fe
in DIP-V-15103 sug-
gests that some primary iron from hemoglobin or ferritin remains
trapped within the inclusion. SEM analyses show that pyrite
) is also present, but not as a signiﬁcant contributor to the
distribution of iron within the specimen (Figure S3).
The close contact between the skin and surrounding amber,
paired with the mummiﬁed external appearance of the skin
where it has shriveled across the surface of the vertebrae, sug-
gest one of two scenarios. Either the tail bearer was dead and
partially desiccated before encapsulation, or else it rapidly dried
due to resin interactions. Early-stage drying is further supported
by the limited amount of cloudy amber surrounding the tail (Fig-
ures 1C and S2), which is a preservational feature related to
decay products or moisture interacting with resin . However,
drying and resin impregnation were not sufﬁcient to preserve
cellular detail in the soft tissues. Based on the clays observed
where bone breaches the amber surface, skeletal material was
likely exposed on the surface after resin polymerization. The
bone has been partially dissolved and inﬁlled with clay from
the surrounding matrix , much like insect body cavities in
this deposit (Figure S2A). Presence of Fe
within the carbonized
remains suggests that organic components were trapped early
and remained undisturbed by subsequent events. Further taph-
onomic constraints are difﬁcult to infer. It is unclear whether the
lack of melanosomes within the keratin sheets of the surrounding
feathers (Figures 2B and S3) might provide additional tapho-
nomic information or whether their absence results from weakly
pigmented feathers or the small sample area available for
SEM analyses. Artiﬁcial maturation experiments  have
shown the breakdown of modern melanosomes at a range of
temperatures, but this work was conducted at temperatures
that would also degrade amber. The taphonomic pathway that
led to the preservation of DIP-V-15103 is not entirely clear, but
it suggests promise for more detailed examinations of organics
or pigmentation in vertebrate inclusions.
SR X-ray mCT scanning of DIP-V-15103 (Figure 1) revealed that
soft tissues have a density insufﬁciently different from the
partially replaced skeletal elements to permit X-ray imaging
and virtual dissection of osteology alone. Consequently, many
diagnostic and comparative osteological details remain
obscured. However, two vertebrae are clearly delineated
ventrally (Figures 1F–1H). Extrapolating lengths of these verte-
brae, the preserved tail section contains at least eight full verte-
brae and part of a ninth. The vertebrae are elongate, with antero-
posterior lengths double the maximum diameter of the tail (Table
S1). Vertebral proportions and tail ﬂexion preclude membership
within the Pygostylia [as in 24]. Even with the skin adpressed to
the bony surface, no features other than the grooved ventral sulci
of two centra are clearly visible. This lack of topography suggests
that the vertebrae lack prominent neural arches, transverse pro-
cesses, or hemal arches. Therefore, the preserved segment is
only a small mid to distal portion of what was likely a relatively
long tail, with the total caudal vertebral count not reasonably
less than 15, and likely greater than 25. Based on specimen
size, it also seems likely that the tail belonged to a juvenile.
DIP-V-15103 is interpreted as a non-avialan coelurosaur tail:
its vertebral proﬁles and estimated length rule out avebrevicau-
dan birds, oviraptorosaurs, and scansoriopterygians—lineages
generally characterized by a short caudal series with subequal
centra [25–27], with the exception of Epidendrosaurus. The
branched feathers have a weak pennaceous arrangement of
barbs consistent with non-avialan coelurosaurs, particularly
paravians. Although the feathers are somewhat pennaceous,
none of the observed osteological features preclude a compsog-
nathid  afﬁnity. The presence of pennaceous feathers in pairs
down the length of the tail may point toward a source within Pen-
naraptora , placing a lower limit on the specimen’s phyloge-
netic position. However, the distribution and shape of the
feathers only strongly supports placement crownward of basal
coelurosaurs, such as tyrannosaurids and compsognathids. In
terms of an upper limit, the specimen can be conﬁdently
excluded from Pygostylia; in addition, it can likely be excluded
from the long-tailed birds, based on pronounced ventral grooves
on the vertebral centra. Additional taxonomic assessment de-
tails are provided in the Supplemental Information.
Both SR X-ray mCT reconstruction and standard light micro-
scopy conﬁrm feather attachments throughout the preserved
tail length (Figure 1). A bilaterally paired series of posterodorsally
oriented feathers extends from the dorsal midline (Figures 1D
and 1E). Another row of feathers is present at mid-height on
each side of the tail, with feathers extending posterolaterally at
roughly 45to its long axis (Figures 1D–1G). These follicle pairs
appear evenly spaced along the length of the tail. Where the out-
lines of two vertebral centra are visible, follicles are located at the
mid-lengths of centra and at intervertebral joints. Ventral
plumage is sparse, consisting of ﬁne feathers that follow the
long axis of the tail closely (Figures 1B, 1G, and 1H). Overall,
the plumage forms laterally directed keels on either side of the
vertebral column, providing a unique opportunity to observe
feather counts and orientations within the contour-like caudal
plumage of a coelurosaur. DIP-V-15103 does not show the
splaying of large pennaceous rectrices observed alongside the
posteriormost caudals of long-tailed birds . Either splaying
was absent in this individual or it was only present caudally,
beyond the preserved region. Nevertheless, the arrangement
of feathers into lateral keels in DIP-V-15103 is similar to the para-
vian tail fan or frond . Such arrangements, composed of
different feather types, can occur not just at the distal tip but
also along the entire length of the tail. Amber preservation
Arrowheads in (A) and (D) mark rachis of feather featured in Figure 4A. Asterisks in (A) and (C) indicate carbonized ﬁlm (soft tissue) exposure. Arrows in (B) and
(E)–(G) indicate shared landmark, plus bubbles exaggerating rachis dimensions; brackets in (G) and (H) delineate two vertebrae with clear transverse expansion
and curvature of tail at articulation. Abbreviations for feather rachises: d, dorsal; dl, dorsalmost lateral; vl, ventralmost lateral; v, ventral. Scale bars, 5 mm in (A),
(B), (D), and (F) and 2 mm in (C), (E), (G), and (H). See also Figure S2.
3354 Current Biology 26, 3352–3360, December 19, 2016
suggests that the tail fans and fronds preserved in paravians are
not merely a taphonomic artifact of compression.
If DIP-V-15103 indeed represents a juvenile coelurosaur tail,
the feathers most likely characterize adult plumage; however,
there is some room for uncertainty. Basal taxa within Pennarap-
tora, such as Similicaudipteryx, are thought to have undergone
dramatic molts that affected the tail region , while some
basal members of Pygostylia have precocial juveniles with
adult-like plumage . The pennaceous feathers and bar-
bules of DIP-V-15103 suggest an adult-like plumage, in which
Figure 2. SR m-XFI Maps and Scanning Electron Micrographs of DIP-V-15103
(A) Elemental maps and region of interest (ROI) image for exposed soft tissue preservation in DIP-V-15103; black carbon ﬁlm surrounds clay minerals inﬁlling void
between vertebrae or partially replacing them; milky amber related to decay surrounds vertebrae and plumage (ROI prior to clay ﬂake removal is better visible in
(B) Patchy keratin preservation with traces of ﬁbrous structure in DIP-V-15103 ventral feather.
(C) Fibrous keratin sheets and isolated melanosomes from barb of modern Indian peafowl (Pavo cristatus; Galliformes).
Scale bars, 2 mm in (A) and 1 mm in (B) and (C). See also Figure S3.
Current Biology 26, 3352–3360, December 19, 2016 3355
feathers would not have been replaced by different morpho-
types in subsequent molts. Alternatively, the feather bearer
may not have conformed to the molt patterns found in modern
The feathers of DIP-V-15103 are similar to each other in
morphology, regardless of position on the tail (Figures 3 and
S4). All preserved feathers have a weakly deﬁned rachis that is
nearly indistinguishable from the barb rami apically and that is
Figure 3. Photomicrographs of DIP-V-15103 Plumage
(A) Pale ventral feather in transmitted light (arrow indicates rachis apex).
(B) Dark-ﬁeld image of (A), highlighting structure and visible color.
(C) Dark dorsal feather in transmitted light, apex toward bottom of image.
(D) Base of ventral feather (arrow) with weakly developed rachis.
(E) Pigment distribution and microstructure of barbules in (C), with white lines pointing to pigmented regions of barbules.
(F–H) Barbule structure variation and pigmentation, among barbs, and ‘rachis’ with rachidial barbules (near arrows); images from apical, mid-feather, and basal
Scale bars, 1 mm in (A), 0.5 mm in (B)–(E), and 0.25 mm in (F)–(H). See also Figure S4.
3356 Current Biology 26, 3352–3360, December 19, 2016
slightly thickened basally (Figure 3). Both rachises and barbs are
sub-cylindrical in cross-section. Although the rachis thickens
basally, the maximum diameter near the follicle is approximately
three times that of an adjacent barb ramus (Figures 3 and S4).
Feathers near the anterior end of the dorsal series have the
greatest basal expansion observed among the plumage, with
rachis widths approaching 60 mm(Figures 3,4A, and 4B).
Rachises among these feathers become as narrow as 18 mmin
Figure 4. DIP-V-15103 Structural Overview and Feather Evolutionary-Developmental Model Fit
(A and B) Overview of largest and most planar feather on tail (dorsal series, anterior end), with matching interpretive diagram of barbs and barbules. Barbules are
omitted on upper side and on one barb section (near black arrow) to show rachidial barbules and structure; white arrow indicates follicle.
(C) Evolutionary-developmental model and placement of new amber specimen. Brown denotes calamus, blue denotes barb ramus, red denotes barbule, and
purple denotes rachis [as in 5, 12].
Scale bars, 1 mm in (A) and (B).
Current Biology 26, 3352–3360, December 19, 2016 3357
apical positions, while barb rami have widths ranging from 15
to 23 mm. Within individual feathers, barbs are positioned alter-
nately along the rachis, approaching an opposite arrangement
basally, with wide spacing between and a weak planar arrange-
ment (Figure 4). Flexion within the amber indicates that barb rami
were ﬂexible, and the rachis itself was somewhat ﬂexible. The
open, ﬂexible structure of these feathers is more analogous to
modern ornamental feathers than to ﬂight feathers, showing
structural similarities to the distal components of contour
feathers in certain Anseriformes (Figures 3 and S5). The paired
feather arrangement is similar to rectrices in modern birds, sug-
gesting that tracts had become established in basal tail plumage
before pygostyle development, with tail plumage becoming
more specialized over time. If the entire tail bore plumage similar
to that trapped in DIP-V-15103, the feather bearer would likely
have been incapable of ﬂight.
The feathers of DIP-V-15103 display exquisitely preserved
barbules. Strikingly, the simple barbules branch not only within
individual barbs but also unmodiﬁed from the rachis (Figures 3,
4,S4G, and S4H). In this regard, the feathers are comparable
to the contours of many modern birds, which also possess
some barbules that originate from the rachis (rachidial barbules),
although usually from the proximal barb base and in reduced
form. In DIP-V-15103, barbules branch in an evenly spaced,
paired, and nearly symmetrical manner. This pattern remains
consistent in both proximal and distal barbules, from proximal
to distal barbs, and along the rachis. Barbules are consistently
blade shaped, with pigmentation outlining ﬁve basal cells fol-
lowed by a poorly differentiated pennulum lacking discernible
nodes or nodal protrusions (Figures 3E–3H). Close spacing be-
tween barbules, combined with the orientation of their ﬂattened
surfaces (parallel to the feather’s long axis), yields open-vaned
feathers that are largely pennaceous.
The weakly developed rachis and contiguous barbule branch-
ing in DIP-V-15103 represents a novel combination among
theropods. Within the evolutionary developmental model of
feathers , DIP-V-15103 appears to be intermediate
between stages IIIa (rachis with naked barbs) and IIIb (barbs
with barbules, lacking a rachis), but it does not exactly ﬁt stage
IIIa+b (rachis with barbs bearing barbules) (Figure 4C). In
DIP-V-15103, barbs exhibit an alternating arrangement along a
poorly deﬁned rachis, with nearly dichotomous branching
apically, and barbules continue along the surface of the rachis
and barbs. The weakly developed rachis appears to have formed
through fusion of individual barbs that already possessed bar-
bules (stage IIIb) instead of fusion of naked barbs (stage IIIa)
. The barb branching pattern continues largely uninterrupted
toward the follicle, as do the pervasive, undifferentiated bar-
bules. Unless the condition observed in DIP-V-15103 represents
a secondary reduction of the rachis, the evolutionary pathway for
feathers in this coelurosaur may have been through stage IIIb
(barbs with barbules), not stage IIIa (fusion of naked barbs).
Cytological observations of barbule development along the
barb vane ridge support the evolutionary coupling of barbs and
barbules [19, 30]. Feather morphology of DIP-V-15103 contrasts
with the reduced rachis and long, naked, ﬁlamentous barbs in
the branched caudal plumage of the dromaeosaurid Sinornitho-
saurus [6, 8] and the therizinosauroid Beipiaosaurus . This
suggests either a greater diversity of tail plumage in coelurosau-
rians than previously suspected or a simpliﬁed form of more-
derived pennaceous feathers in DIP-V-15103.
The unusual barbule conﬁguration in DIP-V-15103 suggests
that barbules were primitively distributed evenly throughout
the length of the feather and only later became restricted to
the barbs and proximal rachis and oriented so that their edges
face the feather surfaces, as in modern avians. In modern birds,
barbule cells originate in the subperiderm and merge into a
syncytium on either side of the barb vane ridge [32, 33]. The
symmetrical arrangement of barbules along the barbs in
DIP-V-15103 implies symmetry of barbule cells across the
barb vane ridge. The contiguous barbule branching along the
rachis probably occurs along the barb vane ridge leading to
the apicalmost barb. In the lineage leading to birds, the bar-
bules became spatially restricted to the barbs and the proximal
portion of the rachis, presumably to accommodate increasing
barb number and density related to rigid pennaceous feathers
(stage IIIa+b and/or stage IV) . Alternatively, the barbule
pattern in DIP-V-15103 may represent a highly derived and
potentially experimental character state unrelated to the avian
lineage. Whichever the case, DIP-V-15103 suggests that
non-avialan theropods had a greater variety of feather forms
than predicted from developmental phenotypes in modern
feathers [4, 5, 10].
Traces of pigmentation exist within the entombed plumage.
Discrete bands corresponding to basal cells within each barbule
are visible due to loosely conﬁned pigments (Figures 3C–3H).
Pigmentation is more pronounced within apical portions of
each barbule and in the barb rami and rachis of dorsal feathers
(Figures 1C and S4H). Coloration varies little within individual
feathers, but dorsal plumage is signiﬁcantly darker than ventral
plumage. Preserved coloration suggests a chestnut brown
dorsal surface, contrasting against pale or almost white ventral
plumage (Figures 1A–1C and S4A–S4D); however, taphonomic
impacts on visible colors are unclear. A small section of the
pale ventral plumage was available for SEM observations. No
melanosomes were observed, suggesting that ventral plumage
was either unpigmented or pigmented through alternative
means, such as carotenoids . Keratin sheets are visible within
the feather layer, displaying the distinctive, porous, laminar
structure also observed in modern avian barbules under SEM
(Figures S2A and S2B).
The theropod tail reported here is an astonishing fossil, high-
lighting the unique preservation potential of amber. Importantly,
in the context of bird origins, feathers and ﬂight are key ele-
ments contributing to the success of the clade. Recent ﬁnds
from Asia [1–4, 6, 8–11] have revealed unexpected diversity in
feather morphologies and ﬂight modes among the proliferation
of small Jurassic-Cretaceous theropods near the origin of birds
with powered ﬂight. DIP-V-15103 adds another morphotype to
this diversity. The integration of developmental studies [5, 7, 33]
and paleontology yields enriched models of morphological
character evolution that help explain major evolutionary transi-
tions in key clades such as theropods, including birds. With
preservation in amber, the ﬁnest details of feathers are visible
in three dimensions, providing concrete evidence for feather
morphologies and arrangement upon the tail, as well as sup-
porting an important role for barbs and barbules in feather
3358 Current Biology 26, 3352–3360, December 19, 2016
DIP-V-15103 was imaged and observed using propagation phase-contrast
Synchrotron Radiation X-ray microtomography (PPC-SR X-ray mCT); standard
microscopy, micro- and macrophotography (including transmitted, incident,
dark-ﬁeld, and UV lighting); and scanning electron microscopy (SEM). Chem-
ical composition was analyzed using Synchrotron Radiation micro-X-ray
ﬂuorescence imaging (m-XFI) and X-ray absorption spectroscopy (XAS). Full
details of experimental procedures for imaging and chemical analyses are pro-
vided in the Supplemental Experimental Procedures. Feather morphological
terms follow  and , while pigmentation terminology follows . Institu-
tional abbreviations include DIP (Dexu Institute of Palaeontology, Chaozhou,
China) and RSM (Royal Saskatchewan Museum, Regina, Canada). Specimen
measurements are based on ocular micrometer readings or 3D reconstruc-
tions (with commentary).
Supplemental Information includes Supplemental Experimental Procedures,
ﬁve ﬁgures, and one table and can be found with this article online at http://
L.X. and R.C.M.: project design, leadership, funding, visualization, and writing;
X.X., W.S.P., T.M., and P.J.C.: morphological analysis and editing; G.L., M.B.,
and Q.Y.: SR phase-contrast CT, 3D modeling, elemental analysis, and edit-
ing; K.T.: taphonomic analysis; M.J.B. and H.R.: data and CT model analysis
and editing; J.Z.: geological background; A.P.W.: SEM analysis and editing.
We thank the Chinese Academy of Science (YZ201211, YZ201509, BASIC
Y5Z003), National Science Fund of China (31672345), State’s Key Project of
Research and Development Plan (2016YFA0401302), National Geographic
Society, USA (EC0768-15), and National Sciences Engineering Research
Council, Canada (2015-00681) for support; Beijing Synchrotron Radiation
Facility (BSRF) and Shanghai Synchrotron Radiation Facility (SSRF) for beam-
time; staffs of 4W1A and 4W1B of BSRF, and 13W of SSRF, for analytical
assistance; Zhao Haifei, Zhang Jie, An Pengfei, and Wang Yanping of BSRF
for research assistance; Ray Poulin (RSM) for discussions; and Nathan Gerein
(University of Alberta) for SEM assistance.
Received: July 10, 2016
Revised: September 7, 2016
Accepted: October 5, 2016
Published: December 8, 2016
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