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LETTERS
A gigantic bird-like dinosaur from the Late Cretaceous
of China
Xing Xu
1
, Qingwei Tan
2
, Jianmin Wang
3
, Xijin Zhao
1
& Lin Tan
2
An evolutionary trend of decreasing size is present along the line to
birds in coelurosaurian theropod evolution
1,2
, but size increases
are seen in many coelurosaurian subgroups, in which large forms
are less bird-like
2,3
. Here we report on a new non-avian dinosaur,
Gigantoraptor erlianensis, gen. et sp. nov., from the Late Cre-
taceous Iren Dabasu Formation of Nei Mongol, China. Although
it has a body mass of about 1,400 kg, a phylogenetic analysis posi-
tions this new taxon within the Oviraptorosauria, a group of small,
feathered theropods rarely exceeding 40 kg in body mass
2,4–7
.A
histological analysis suggests that Gigantoraptor gained this size
by a growth rate considerably faster than large North American
tyrannosaurs such as Albertosaurus and Gorgosaurus
8
. Giganto-
raptor possesses several salient features previously unknown in
any other dinosaur and its hind limb bone scaling and proportions
are significantly different from those of other coelurosaurs
9,10
,
thus increasing the morphological diversity among dinosaurs.
Most significantly, the gigantic Gigantoraptor shows many bird-
like features absent in its smaller oviraptorosaurian relatives,
unlike the evolutionary trend seen in many other coelurosaurian
subgroups
2,3
.
Theropoda Marsh, 1881
Oviraptorosauria Barsbold, 1976
Gigantoraptor erlianensis gen. et sp. nov.
Etymology. The generic name refers to the animal being a gigantic
raptor dinosaur; the specific name is derived from the Erlian basin
where the holotype was collected.
Holotype. LH V0011, an incomplete skeleton preserving a nearly
complete mandible, several partial presacral vertebrae, most caudal
vertebrae, nearly complete right scapula, much of the forelimbs, par-
tial ilium, and nearly complete pubes and hind limbs.
Type locality and horizon. Saihangaobi, Sunitezuoqi, Nei Mongol
Autonomous Region. Iren Dabasu Formation, Senonian, Late
Cretaceous
11
.
Diagnosis. An oviraptorosaur distinguishable from other species in
the following features: a short mandible less than 45% of femoral
length, a fossa on the lateral surface of the dentary close to the anterior
end and a second fossa bounded dorsally by a lateral flange anterodor-
sal to the external mandibularfenestra, a long posteroventral process of
the dentary extending to the level of the glenoid, a small, posteriorly
tapered retroarticular process much deeper than wide, a tail composed
of opisthocoelous anterior caudal vertebrae, amphicoelous middle
ones and procoelous posterior ones, pleurocoels present on most cau-
dal vertebrae, a pair of vertically arranged pneumatic openings present
on the lateral surface of anterior caudal centra, a large pneumatic
opening present on the ventral surface of anterior and middle caudal
centra, anterior caudal vertebrae with tall neural spines (about three
times as tall as wide) and robust and rod-like transverse processes
located posteriorly, posteroventral margin of anterior caudal centra
extending considerably ventrally, well-developed laminal system on
the anterior caudal vertebrae (prespinal, postspinal, spinopostzygapo-
physeal, anterior centrodiapophyseal, posterior centrodiapophyseal,
and prezygodiapophyseal laminae present on anterior caudal verteb-
rae), middle caudal vertebrae with vertical prezygapophyseal articular
facets located proximal to the distal extremity of the process, a prom-
inent convexity ventral to the acromion processon the lateral surfaceof
the scapula, a laterally bowed humerus with a prominent, spherical
humeral head and a strongly medially curved deltopectoral crest, a
centrally constricted thick ridge running along the posterior margin
of the proximal half of the humerus, a straight ulna with a sub-circular,
concave proximal articular surface, a radius with a sub-spherical distal
end, metacarpal I with a slightly convex medial margin of the proximal
end and a medial condyle three times as high as and extending much
more distally than the lateral one on the distal end, a metacarpal II with
a prominent dorsolateral process on the proximal end and a longit-
udinal groove on the ventral margin of the proximal third of the shaft,
manual unguals with a triangular set of lateral grooves, a laterally
compressed pubis, a femur with a straight shaft, a constricted neck
between the posteromedially oriented, spherical femoral head and
the anteroposteriorly wide trochanteric crest which is much more
robust and higher anteriorly than posteriorly, a distinct narrow groove
medial to the trochanteric crest extending down the posterior margin
of the femoral shaft, and a patellar groove present on the anterior
surface of the distal end, a small calcaneum obscured from anterior
view by the wide astragalar main body, a proximal projection on the
lateral margin of distal tarsal IV, metatarsal III with ginglymoid distal
end, and pedal unguals with two lateral grooves and a constricted
proximal articular surface (Fig. 1b–g, i–t).
Description and comparison. The Gigantoraptor holotype is esti-
mated to be 8 m in total length and 3.5 m high at the hip (Fig. 1a)
and to be about 1,400 kg in body mass (see Supplementary
Information). The mandible is intermediate in morphology between
basal oviraptorosaurs and highly specialized oviraptorids
12–15
: the
mandible is comparable to that of Oviraptor philoceratops in relative
depth, the mandibular symphysis is U-shaped with an extended shelf,
the large external mandibular fenestra is relatively shallow and is
located more anteriorly than in basal oviraptorosaurs but less so than
in oviraptorids, the dentary is edentulous, dorsoventrally deep, and
posteriorly bifurcated, the coronoid region is high but lacks a dor-
somedially extended surangular process, the surangular lacks a
anterior projection to divide the external mandibular fenestra and is
not as enlarged as in oviraptorids, and the glenoid articulation is
convex in lateral view and expanded transversely (Fig. 1b, c). As in
Caenagnathidae
13,15
, the mandibular symphysis is completely fused
without any trace of suture (Fig. 1c).
Postcranially, Gigantoraptor also displays numerous derived
similarities seen in the Oviraptorosauria or its more exclusive
1
Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
2
Long Hao Institute of Geology and Paleontology,
3
Department of
Land Resources, Hohhot, Nei Mongol 010010, China.
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groups
12,13,16
: a deep groove present on the ventral surface of the
caudal vertebral centra, short middle and posterior caudal vertebrae
with dorsoventrally compressed centra, ventrally located transverse
processes present on the posterior caudal vertebrae, caudal neural
arches positioned on the anterior half of the respective centra, a
radius as long as the ulna, and a pubis with a concave anterior margin.
Like other oviraptorosaurs
12,13
, the caudal vertebrae are pneumatic,
but in a previously unknown manner: the anterior caudal vertebrae
bear a pair of vertically arranged pneumatic foramina on the central
lateral surface (Fig. 1d) and a large pneumatic opening on the central
ventral surface (Fig. 1g). Interestingly, despite a lack of pneumatic
opening, the posterior caudal centra have spongy internal structures
(Fig. 1h), superficially similar to those of the sauropod group
Titanosauria, a feature probably related to weight saving
17
.
However, Gigantoraptor exhibits many features that are not
seen in other oviraptorosaurians but do occur in more derived
maniraptorans
2,3,18,19
. The anterior caudal centra are wider transver-
sely than deep dorsoventrally. The scapular blade is shallower distally
without an expanded distal end. The forelimbs are proportionally
long, with a humerus1radius1metacarpal II to femur1tibiotarsus1
metatarsal III ratio of 0.60. The radius bears a sub-spherical distal end.
Metacarpal I is less than one-third the length of metacarpal II and the
latter is much more robust than the former (Fig. 1n). The pubis is
laterally compressed and straplike for most of its length, though a
long pubic symphysis is present. The femur is avian-like in having a
spherical femoral head with a distinct neck, a high and prominent
trochanteric crest much thicker and higher anteriorly than poster-
iorly (Fig. 1q), a shallow popliteal fossa distally bounded by a low
shelf, and lacks a fourth trochanter. The tibia has a lateral margin sub-
equal in depth to the medial margin on the distal end. The astragalar
main body extends laterally to hide the small calcaneum from
anterior view (Fig. 1s). A distinct proximal projection is present on
lfl
b
c
i
k
m
n
o
t
p
a
d
e
f
g
s
r
q
h
jl
afo
pfo
pvpa
ra
es
hh
dpc
dpc
dlp
lc
dg
dg
vg
vg
g
pg
fh
am
ap
fc
vo
g
prf
pf
tp
spl
vp
dp
c
tc
Figure 1
|
Skeletal anatomy of Gigantoraptor holotype (LH V0011).
a
, Skeletal reconstruction showing preserved elements, with a 175-cm-tall
man for a scale. Bones are: mandible in lateral (
b) and dorsal (c) views;
anterior caudal vertebra in lateral (
d) and posterior (e) views; middle caudal
vertebra in lateral (
f) and ventral (g) views; computed tomographic scan of a
posterior caudal vertebral centrum showing the spongy internal structure
(
h); left humerus in anterior (i) and proximal (j) views; left ulna in anterior
(
k) and proximal (l) views; left radius in anterior view (m); left metacarpals I
and II in anterior (
n) and proximal (o) views; manual ungual in lateral view
(
p); right femur in proximal view (q) and left femur in distal view (r); left
tibiotarsus in anterior view (
s); pedal ungual in lateral view (t). Scale bars in
b, c , and p, 5 cm, in d–f, g, n, and t, 3 cm, and in i, k, m, and s, 10 cm.
Abbreviations: afo, anterior fossa; am, astragalar main body; ap, ascending
process; c, calcaneum; dg, dorsal groove; dlp, dorsolateral process; dp, dorsal
pneumatic foramen; dpc, deltopectoral crest; es, extended shelf; fc, fibular
crest; fh, femoral head; g, groove; hh, humeral head; lc, lateral condyle; lfl,
lateral flange; pf, pneumatic foramen; pfo, posterior fossa; pg, patellar
groove; prf, prezygapophysial articular facet; pvpa, articular facet for
posteroventral process of dentary; ra, retroarticular process; spl,
spinopostzygapophyseal lamina; tc, trochanteric crest; tp, transverse
process; vg, ventral groove; vo, ventral opening; vp, ventral pneumatic
foramen.
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the lateral margin of tarsal IV and metatatarsal III is ginglymoid
distally.
Histological analysis. We have conducted a histological analysis to
determine the longevity, developmental stage, and growth strategy
for the Gigantoraptor holotype (see Supplementary Information). A
mid-diaphyseal petrographic thin section was made from the fibula.
Although the medullary cavity is very small, the secondary osteons
obliterate partial growth record in the inner cortex. A retrocalcula-
tion was thus made to assess the missing ages
20,21
. We calculated the
number of the missing annual intervals by using the average width of
the innermost three growth zones to divide the distance in question,
which resulted in four years missing. The presence of seven sets of
lines of arrested growth (LAGs) and the calculated four missing zones
suggest that the Gigantoraptor holotype probably died during its
eleventh year of life (Fig. 2).
The animal is inferred to be adult, as indicated by the extensive
development of the secondary osteons, a moderate decrease in spa-
cing between LAGs close to the periphery of the bone, and the pres-
ence of the outer circumferential layer comprising of a poorly
vascularized layer of lamellar bone which indicates a slow rate of
bone accretion
20
. Interestingly, the fourth to seventh sets of LAGs,
which are within the outer circumferential layer, are not tightly
packed as in a typical outer circumferential layer. We thus infer that
the animal reached its young adult size within seven years and was
still at relatively early young adult stage at the time of death and
estimate that a full-sized Gigantoraptor is considerably heaver than
1,400 kg. This suggests that Gigantoraptor has an accelerated growth
rate faster than most other theropods, including large North
American tyrannosaurs such as Albertosaurus and Gorgosaurus
8
,a
growth strategy seen in most gigantic dinosaurs
21,22
.
Discussion. As an oviraptorosaurian, Gigantoraptor is remarkable
in its gigantic size (see Supplementary Information), about 300
times as heavy as basal oviraptorosaurians Caudiperyx and Protar-
chaeopteryx
6,23,24
, species known to bear pennaceous arm feathers and
other types of feathers as well. A size disparity so dramatic might
cause a change of integumentary coverings, such that large-sized
forms lose filamentous integuments for insulation, as is the case in
some mammals
25
and is inferred for the tyrannosaurs
26
. But
Gigantoraptor might have at least retained arm feathers or their
homologues from its ancestors, if not other types of feathers, given
that the primary function of arm feathers is not to insulate the indi-
vidual and their development is probably not related to size (see
Supplementary Information).
Phylogenetic analysis posits Gigantoraptor at the base of the
Oviraptoridae (see Supplementary Information), a hypothesis sup-
ported mainly by its mandibular morphology, intermediate between
basal oviraptorosaurian and derived oviraptorid conditions
13,16,27
.
This intermediate systematic position is consistent with its geological
age-Senonian, which is earlier than any other oviraptorids are
known
13,16,27
.
Gigantoraptor possesses a large number of autapomorphies (see
‘Diagnosis’ section), indicating that it represents a highly specialized
lineage in oviraptorosaurian evolution. In particular the presence of
many features unknown in any other dinosaur, such as the highly
specialized caudal vertebrae and the bizarre humerus, suggests that
morphological diversity among the dinosaurs is higher than prev-
iously known. This is further indicated by Gigantoraptor’s unusual
limb allometry. Among theropods, the tibiotarsus and metatarsus
show negative allometry relative to the femur when size increases
9,28
and limb circumference scales to limb length
10
, though other factors,
including phylogeny, contribute to the relative proportions and
robustness of the limb elements as well
9
. A comparison of the femur
circumference-to-length ratio, tibiotarsus-to-femur length ratio and
metatarsus-to-femur length ratio values in Gigantoraptor and ovir-
aptorids indicates that Gigantoraptor has values similar to those in its
much smaller relatives (Table 1) and significantly different from the-
oretically predicted ones
9,10,28
. This is inconsistent with a general pat-
tern that large-sized members of non-avian theropod sub-groups have
proportionally stouter limbs and shorter lower legs than their small-
sized relatives
9
. Compared with other similar-sized theropods includ-
ing tyrannosauroids, Gigantoraptor has much more slender limbs and
longer lower legs as indicated by the femur circumference-to-length
ratio, tibiotarsus-to-femur length ratio and metatarsus-to-femur
length ratio values (Table 1), suggesting that it might be the most
cursorial theropod of comparable size.
Gigantoraptor is an exception to some general patterns seen during
the gigantism of non-avian theropods. Contrary to the evolutionary
trend of size decrease in coelurosaurian evolution
1,2
, which plays a
key part in the origin of birds
2,3,29
, most non-avian coelurosaurian
subgroups display a trend of size increase and their large-sized mem-
bers tend to reverse to more primitive conditions in many bird-like
characters
2,3
. The discovery of Gigantoraptor complicates this pat-
tern, however. Although much larger than its close relatives,
Gigantoraptor has proportionally the longest forelimb among ovir-
aptorosaurs
6,12,13
, a manus resembling basal eumaniraptorans, bird-
like hind limbs, and many other advanced features. These features are
close to the conditions in birds but absent in other smaller ovirap-
torosaurs
13
, indicating an unusual pattern for the Oviraptorosauria
among the non-avian coelurosaurian subgroups.
Received 9 February; accepted 18 April 2007.
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1,000 mm
Figure 2
|
Photograph of transverse thin section of the fibular mid-shaft of
Gigantoraptor holotype (LH V0011) under a polarized scope.
The section
shows seven sets of single, paired, or grouped LAGs. Paired or grouped LAGs
are seen in some non-avian and avian dinosaurs, some mammals and some
ectothermic vertebrates
20
.
Table 1
|
Relative proportions of selected limb elements in oviraptorosaurs
and some large theropods
Taxa Femur
circumference/
femur length
Tibiotarsus
length/femur
length
Metatarsus
length/femur
length
Gigantoraptor (femur length: 110 cm) 0.32 1.07 0.53
Oviraptorids (femur length: 15
–
30 cm) 0.34 1.23 0.55
Tyrannosauroids (femur length:
100
–
120 cm)
0.39 0.90 0.54
Carnosaurs and ceratosaurs (femur
length: 100
–
120 cm)
0.40 0.86 0.39
Data were collected from original specimens or published literature
9,10,30
.
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Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements We thank A. Chinsamy-Turan and G. M. Erickson for
discussions on bone histology and critical comments on the histological section,
J. A. Clark for comments on the mansuscript, the technicians of the Long Hao
Institute of Geology and Paleontology for contributions in the field and for
preparation of fossil materials, R.-S. Li and W.-D. Zhang of the Institute of
Vertebrate Paleontology and Paleoanthropology for drawings and photography.
X.X’s work is supported by grants from the Chinese Academy of Sciences, the
National Natural Science Fondation of China, and the American Museum of
Natural History. The fieldwork was supported by grants from the Ministry of Land
and Resources PRC and the Department of Land and Resources of Nei Mongol.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial interests.
Correspondence and requests for materials should be addressed to X.X.
(xu.xing@ivpp.ac.cn).
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