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Gigantic bird-like dinosaur from the Late Cretaceous of China

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An evolutionary trend of decreasing size is present along the line to birds in coelurosaurian theropod evolution, but size increases are seen in many coelurosaurian subgroups, in which large forms are less bird-like. Here we report on a new non-avian dinosaur, Gigantoraptor erlianensis, gen. et sp. nov., from the Late Cretaceous Iren Dabasu Formation of Nei Mongol, China. Although it has a body mass of about 1,400 kg, a phylogenetic analysis positions this new taxon within the Oviraptorosauria, a group of small, feathered theropods rarely exceeding 40 kg in body mass. 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. Gigantoraptor 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, 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.
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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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 df, 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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Figure 2
|
Photograph of transverse thin section of the fibular mid-shaft of
Gigantoraptor holotype (LH V0011) under a polarized scope.
The section
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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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... Oviraptorosaurs ranged from chicken-or turkey-sized [3,4], to species which likely weighed more than a tonne [5]. Based on their cranial morphology, this diverse clade contained both omnivorous and herbivorous members [12,[21][22][23]. ...
... Oviraptorosauria was a clade of maniraptoran theropods characterized by a foreshortened rostrum, often bearing an edentulous beak, and highly pneumatic skeletons, a combination that easily distinguishes them from other theropod groups [1]. Oviraptorosaurs are known from well-preserved fossils, primarily from Asia, that have yielded insight into the biology, morphology, diversity, and evolutionary history of this peculiar group of theropods [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The earliest certain oviraptorosaurs are known from the Barremian stage of the Early Cretaceous, between 125-129 million years ago [20,21] [32,34,38,42], although this has not been reevaluated since that species was transferred to a new genus. ...
... The morphology of Eoneophron infernalis is broadly consistent with that of other caenagnathids, but it provides additional information on their proportions and variation. There is a negative allometric relationship between tibia and femur length in Oviraptorosauria [73]; E. infernalis proportions are scaled similarly to those of Anzu wyliei, Chirostenotes pergracilis, Elmisaurus rarus, and Gigantoraptor [5,8,12,62], suggesting that this negative allometry is conserved across caenagnathids. Several discrete morphological features indicate that Eoneophron infernalis is distinct from Anzu wyliei and other caenagnathids. ...
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Caenagnathidae is a clade of derived, Late Cretaceous oviraptorosaurian theropods from Asia and North America. Because their remains are rare and often fragmentary, caenagnathid diversity is poorly understood. Anzu wyliei is the only caenagnathid species currently described from the late Maastrichtian Hell Creek Formation of the USA and is also among the largest and most completely preserved North American caenagnathids. Smaller, less complete caenagnathid material has long been known from the Hell Creek Formation, but it is unclear whether these are juvenile representatives of Anzu or if they represent distinct, unnamed taxa. Here, we describe a relatively small caenagnathid hindlimb from the Hell Creek Formation, and conduct osteohistological analysis to assess its maturity. Histological data and morphological differences from Anzu wyliei and other caenagnathids allow us to conclude that this specimen represents a new species of caenagnathid from the Hell Creek Formation, with a smaller adult body size than Anzu. This new taxon is also distinct from other small caenagnathid material previously described from the area, potentially indicating the coexistence of three distinct caenagnathid species in the Hell Creek Formation. These results show that caenagnathid diversity in the Hell Creek ecosystem has been underestimated.
... Few groups of theropods show pneumatic traits with external manifestation in their caudal vertebrae. A pleurocoel is present on the lateral surface of the centra of Megaraptora, Oviraptorosauria, Therizinosauria, and possibly Torvosaurus (e.g., Britt, 1991Britt, , 1993Zhang et al., 2001;Xu et al., 2007;Zanno et al., 2009;Benson, Carrano & Brusatte, 2010;Balanoff & Norell, 2012). However, Megaraptora is the only clade with highly pneumatized caudal vertebrae, extending to the centra and the neural arches (Coria To date, the only theropods to exhibit foramina on the dorsal surface of the caudal neural arches are Acrocanthosaurus and Meraxes (Fig. 29I), while Giganotosaurus has only shallow depressions (Britt, 1993;Aranciaga Rolando, Garcia Marsá & Novas, 2020;Canale et al., 2022). ...
... Among other theropod groups, Ornithomimosauria shows evidence of pneumatization in only the neural arches of the anterior and middle caudal vertebrae (Watanabe et al., 2015), while in Therizinosauroidea, penumaticity is observed mainly in the anterior vertebrae (neural arch and centrum; e.g., Zanno et al., 2009;Zanno, 2010). Finally, oviraptorosaurs hold pneumatic foramina in anterior, middle, and posterior caudal centra (e.g., Xu et al., 2007;Balanoff & Norell, 2012). Among non-tetanuran theropods (and possibly among non-avetheropodan theropods), Brachyrostra appears to be the only clade characterized by having pneumatic caudal vertebrae, as shown in the present study. ...
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Aucasaurus garridoi is an abelisaurid theropod from the Anacleto Formation (lower Campanian, Upper Cretaceous) of Patagonia, Argentina. The holotype of Aucasaurus garridoi includes cranial material, axial elements, and almost complete fore- and hind limbs. Here we present a detailed description of the axial skeleton of this taxon, along with some paleobiological and phylogenetic inferences. The presacral elements are somewhat fragmentary, although these show features shared with other abelisaurids. The caudal series, to date the most complete among brachyrostran abelisaurids, shows several autapomorphic features including the presence of pneumatic recesses on the dorsal surface of the anterior caudal neural arches, a tubercle lateral to the prezygapophysis of mid caudal vertebrae, a marked protuberance on the lateral rim of the transverse process of the caudal vertebrae, and the presence of a small ligamentous scar near the anterior edge of the dorsal surface in the anteriormost caudal transverse process. The detailed study of the axial skeleton of Aucasaurus garridoi has also allowed us to identify characters that could be useful for future studies attempting to resolve the internal phylogenetic relationships of Abelisauridae. Computed tomography scans of some caudal vertebrae show pneumatic traits in neural arches and centra, and thus the first reported case for an abelisaurid taxon. Moreover, some osteological correlates of soft tissues present in Aucasaurus and other abelisaurids, especially derived brachyrostrans, underscore a previously proposed increase in axial rigidity within Abelisauridae.
... In contrast to other Upper Cretaceous localities in the Gobi Desert where medium-sized dinosaurs were predominantly recovered, the Iren Dabasu Formation presents a unique composition. Comprising light grey fluvial fine sandstone, mudstone and siltstone, and primarily exposed within the Erlian Basin at the southeast rim of the Gobi Desert (Currie and Eberth, 1993;Xing et al., 2012), this geologic formation is characterized by the abundance of large-sized herbivorous dinosaurs (Gilmore, 1933a, b;Zhang et al., 2001;Xu et al., 2006Xu et al., , 2007. True paravian theropods, including troodontids and dromaeosaurids, are scarcely represented (Currie and Dong, 2001;Xing et al., 2012). ...
Article
Tooth attachment and replacement play significant roles in the feeding ecology of polyphyodont vertebrates, yet these aspects have remained largely unexplored in non-avialan paravians including troodontids. Here, we describe a new troodontid species, Urbacodon norelli sp.n., recovered from the Upper Cretaceous Iren Dabasu Formation of Inner Mongolia, China, based on an incomplete right dentary and 12 associated replacement teeth. U. norelli is distinguished from all other known troodontids, including its relative U. itemirensis from Uzbekistan, by several features: the presence of paired dentary symphyseal foramina, the presence of a relatively steep anterior margin of the dentary, the absence of a dentary chin, the presence of a common groove hosting the anterior 12 dentary teeth, and the presence of relatively larger dentary teeth. Phylogenetic analysis places both species of Urbacodon as sister taxa to Zanabazar junior, confirming their status as later-diverging troodontids. Radiographs revealed an alternating tooth replacement pattern in U. norelli, with a maximum Zahnreihen-spacing estimated to be 3. During tooth replacement, the anteriorly inclined interdental septa, which wedge between anterior dentary teeth, underwent frequent remodelling as the developing tooth moved upwards, particularly anterolabially. This rapid turnover left insufficient time for an interdental plate to form, resulting in the absence of such structures in this specimen. The frequent remodelling of periodontal tissues accompanying tooth replacement is likely to account for the absence of interdental plates. The discovery of this new troodontid expands our understanding of paravian theropods from the Upper Cretaceous Iren Dabasu Formation and provides valuable insights into troodontid tooth biology.
... Therizinosaurus; Senter & James, 2010;Zanno & Makovicky, 2011;Deinocheirus;; note that the phylogenetic analysis used in this study supports therizinosauroids as non-maniraptorans and sister taxa of the ornithomimosaurs). Among maniraptorans, only a few oviraptorosaurs are known to reach size class 6 (e.g., Gigantoraptor; Xu et al., 2007;Tanaka et al., 2018), whereas no paravian is known at size classes higher than 5 (Holtz, 2021;Sues et al., 2022). This pattern constrasts with the large number of non-maniraptoran lineages which successfully occupied the largest size classes (Paul, 1988;Sereno & Brusatte, 2008;Carrano et al., 2012;Holtz, 2021), and suggests a combination of clade-specific factors negatively biasing maniraptoran diversification at giant body size. ...
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Known since the 19 th Century, the compsognathids are among the smallest predatory dinosaurs, and include the first feathered non-avian species found. Traditionally, compsognathids have been considered small and unspecialized coelurosaurs, closer to birds than large-bodied forms like allosauroids and megalosaurids. Yet, all known compsognathids are based on skeletally-immature specimens, and this challenges the accuracy of their traditional phyletic placement. Despite the role of heterochrony in dinosaur evolution is widely recognized, the impact of ontogenetic-biased miscodings in shaping theropod phylogenetics is mostly underestimated. Herein, I show that the standard framework of theropod macroevolution is biased by a series of coding artifacts which violate semaphoront equality prescribed by phylogenetic systematics. I introduce "Ontogenetic State Partitioning" (OSP), a novel coding protocol which integrates ontogenetic and morphological variation under a total evidence approach, and apply it to a densely sampled data set focusing on Mesozoic theropods. The phylogenetic analysis dismissed "Compsognathidae" from being a natural group: its members are identified as juvenile morphs nested among several non-maniraptoriform tetanuran lineages. Conservatism in the immature body plan and greater disparity among large-sized adults differentiate the predatory communities dominated by non-coelurosaurian species (e.g., the so called "triumvirates") from the maniraptoriform-tyrannosaurid faunas (herein named "tyrannies"). This clade-specific differentiation among the communities is confirmed by an analysis of the predatory guild structures including all growth stages: triumvirates and tyrannies result as particular cases along a continuum of communities regulated mainly by alternative contributions of the small-and medium-sized classes. The oldest tyrannies (early Late Cretaceous in age) cluster among non-tyranny communities, supporting the hypothesis that tyrannosaurid-dominated faunas acquired their peculiar structure only after the extinction of the non-coelurosaurian components. The macroevolutionary trajectory that led the maniraptoriforms to realize the avian-like biology may have precluded them from occupying hypercarnivorous large-bodied niches: this bauplan constraint would have favored the tyrannosauroids in opportunistically assuming the apex predatory roles in Late Cretaceous Asiamerica but not elsewhere. The large-scale structure of the Cenozoic radiation of birds is coherent with the framework introduced herein.
... Oviraptorosauria, a clade of maniraptoran theropod dinosaurs from the Cretaceous of Laurasia 1,2 , is currently represented by approximately 50 genera 2,3 , which range from chicken-sized forms to the approximately eightmetre long, two-tonne Gigantoraptor erlianensis 4 . The group has become famous for their preserved eggs and nesting behaviours, from which circumstances they also derive their name [5][6][7][8] . ...
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Oviraptorosaurians were a theropod dinosaur group that reached high diversity in the Late Cretaceous. Within oviraptorosaurians, the later diverging oviraptorids evolved distinctive crania which were extensively pneumatised, short and tall, and had a robust toothless beak, interpreted as providing a powerful bite for their herbivorous to omnivorous diet. The present study explores the ability of oviraptorid crania to resist large mechanical stresses compared with other theropods and where this adaptation originated within oviraptorosaurians. Digital 3D cranial models were constructed for the earliest diverging oviraptorosaurian, Incisivosaurus gauthieri, and three oviraptorids, Citipati osmolskae, Conchoraptor gracilis, and Khaan mckennai. Finite element analyses indicate oviraptorosaurian crania were stronger than those of other herbivorous theropods (Erlikosaurus and Ornithomimus) and were more comparable to the large, carnivorous Allosaurus. The cranial biomechanics of Incisivosaurus align with oviraptorids, indicating an early establishment of distinctive strengthened cranial biomechanics in Oviraptorosauria, even before the highly modified oviraptorid cranial morphology. Bite modelling, using estimated muscle forces, suggests oviraptorid crania may have functioned closer to structural safety limits. Low mechanical stresses around the beaks of oviraptorids suggest a convergently evolved, functionally distinct rhamphotheca, serving as a cropping/feeding tool rather than for stress reduction, when compared with other herbivorous theropods.
... Firsthand Firsthand ) (Ji et al., 1998) Caenagnathidae Gigantoraptor erlianensis LH V0011 Firsthand (Xu et al., 2007;Ma et al., 2017) Anzu wyliei CM 78000 Firsthand (Lamanna et al., 2014) Caenagnathus collinsi CMN 8776 Literature (Currie et al., 1993) Chirostenotes pergracilis TMP 2001.12.12 Literature (Funston and Currie, 2014) Oviraptoridae Oviraptor philoceratops AMNH 6517 Firsthand (Osborn et al., 1924) Rinchenia mongoliensis MPC-D 100/32A Literature (Funston et al., 2017) Citipati osmolskae IGM 100/978 Firsthand (Clark et al., 2002) Huanansaurus ganzhouensis HGM41HIII-0443 Firsthand (Lü et al., 2015) Tongtianlong limosus DYM-2013-8 Firsthand (Lü et al., 2016) Banji long IVPP V16896 Firsthand (Xu and Han, 2010) Khaan mckennai IGM 100/973 Firsthand (Balanoff and Norell, 2012) Jiangxisaurus ganzhouensis HGM41HIII0421 Firsthand (Wei et al., 2013) Nemegtomaia barsboldi MPC-D 100/2112 Literature (Lü et al., 2004) Avialae Jeholornis prima Reconstruction Literature (Xu et al., 2011) Sapeornis chaoyangensis Reconstruction of IVPP V13275 and V13276 ...
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Oviraptorosauria and Scansoriopterygidae are theropod clades that include members suggested to have partially or fully herbivorous diets. Obligate herbivory and carnivory are two ends of the spectrum of dietary habits along which it is unclear how diet within these two clades might have varied. Clarifying their diet is important as it helps understanding of dietary evolution close to the dinosaur-bird transition. Here, diets are investigated by conventional comparative anatomy, as well as measuring mandibular characteristics that are plausibly indicative of the animal's feeding habit, with reference to modern herbivores that may also have nonherbivorous ancestry. In general, the skulls of scansoriopterygids appear less adapted to herbivory compared with those of oviraptorids because they have a lower dorsoventral height, a smaller lateral temporal fenestra, and a smaller jaw-closing mechanical advantage and they lack a tall coronoid process prominence. The results show that oviraptorid mandibles are more adapted to herbivory than those of caenagnathids, early-diverging oviraptorosaurians and scansoriopterygids. It is notable that some caenagnathids possess features like an extremely small articular offset, and low average mandibular height may imply a more carnivorous diet than the higher ones of other oviraptorosaurians. Our study provides a new perspective to evaluate different hypotheses on the diets of scansoriopterygids and oviraptorosauri-ans, and demonstrates the high dietary complexity among early-diverging pennaraptorans.
Article
Oviraptorosaurs are among the most diverse and best-known extinct theropod groups. Their bizarre anatomy and their social and reproductive behaviour are now well understood. Among the oviraptorid subclade, the two-fingered Oksoko avarsan is particularly well-represented. It is known from several exquisite skeletons, preserving not only the entire skeleton, but multiple stages through ontogeny, providing an exemplar for understanding the anatomy of oviraptorids and the changes that their skeletons experienced over their lifetimes. Here I comprehensively describe the osteology of Oksoko avarsan and comment on its ontogenetic variation. Excellent preservation of the specimens provides unparalleled detail into the anatomy of an oviraptorid, providing valuable context for interpreting other oviraptorosaurs. Several changes are observed to occur through ontogeny relating to robustness of the bones and proportions of the skeleton, but there is little evidence suggesting that discrete features like the cranial crest arose late in ontogeny. Instead, early development of the cranial crest in oviraptorids, and its internal connection with the nasal passages and other pneumatic spaces, argue in favour of a role in vocalization, perhaps alongside sexual display. Detailed anatomical and ontogenetic data, like those provided by known specimens of Oksoko avarsan, are necessary to help to underpin ongoing research into the palaeobiology and macroevolution of Oviraptorosauria.
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The holotype of Microvenator celer Ostrom, 1970 (AMNH 3041) is a partial skeleton of a small maniraptoran theropod from the Lower Cre-taceous Cloverly Formation of Montana. We present a detailed redescription of this specimen, emphasizing those features that are of interest for discovering the phylogenetic relationships of Mi-crovenator. Based on several postcranial features, especially the lack of fusion of the neurocentral sutures, we consider AMNH 3041 a juvenile individual. Reexamination of the holotype revealed the presence of several autapomorphies that provide the basis for a revised diagnosis of Micro-venator celer. Diagnostic characters include posterior dorsal and caudal vertebrae 'that are wider than high, the presence of a deep depression on the proximomedial part of the pubis, and an accessory trochanteric ridge below the lesser fem-oral trochanter. Phylogenetic analysis places Mi-crovenator either among Oviraptorosauria, or as the sister group to the Oviraptorosauria. Among the characters diagnostic for the Oviraptorosauria, anteriorly concave pubes, a proximodorsal tuber-cle on the manual unguals, and possibly an eden-tulous dentary with a pronounced symphysis are present in Microvenator. M. celer is the earliest known oviraptorosaurian or oviraptorosaur-like theropod represented by diagnostic skeletal remains .
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Oviraptorosauria is a clade of Cretaceous theropod dinosaurs of uncertain affinities within Maniraptoriformes. All previous phylogenetic analyses placed oviraptorosaurs outside a close relationship to birds (Avialae), recognizing Dromaeosauridae or Troodontidae, or a clade containing these two taxa (Deinonychosauria), as sister taxon to birds. Here we present the results of a phylogenetic analysis using 195 characters scored for four outgroup and 13 maniraptoriform (ingroup) terminal taxa, including new data on oviraptorids. This analysis places Oviraptorosauria within Avialae, in a sister-group relationship with Confuciusornis. Archaeopteryx, Therizinosauria, Dromaeosauridae, and Ornithomimosauria are successively more distant outgroups to the Confuciusornis–oviraptorosaur clade. Avimimus and Caudipteryx are successively more closely related to Oviraptoroidea, which contains the sister taxa Caenagnathidae and Oviraptoridae. Within Oviraptoridae, “Oviraptor” mongoliensis and Oviraptor philoceratops are successively more closely related to the Conchoraptor–Ingenia clade. Oviraptorosaurs are hypothesized to be secondarily flightless. Emended phylogenetic definitions are provided for Oviraptoridae, Caenagnathidae, Oviraptoroidea, Oviraptorosauria, Avialae, Eumaniraptora, Maniraptora, and Maniraptoriformes.
Chapter
Troodontidae is a clade of small, lightly built maniraptorans known from Cretaceous deposits of Asia and North America. These theropods have serrated teeth, raptorial hands, and an enlarged sickle-shaped claw on the foot. This chapter discusses the taxonomy and diagnostic features of troodontids. It also discusses phylogenetic hypotheses of troodontid relationships. Diagnostic remains of troodontids are largely restricted to Central Asia and China, and the origin and most of the evolutionary history of the clade was endemic to that continent. Only a single derived troodontid taxon, Troodon formosus, occurs in North America.
Chapter
This chapter focuses on Oviraptorosauria, a group of Cretaceous maniraptoran theropods. Oviraptorosaurs had massive toothless jaws, and tall, median bony crests, or casques, sometimes surmounted their shortened, deep, and highly pneumatized skulls. The members of the Oviraptorosaurian clade include Avimimus, Caudipteryx, Incisivosaurus, Citipati, Rinchenia, Ingenia, Conchoraptor, and Khaan. Oviraptorosaurs are distributed in Late Cretaceous depositional environments in Central Asia and North America.
Article
Since the discovery of dinosaurs in the Iren Dabasu Formation at Iren Nor in 1922, several expeditions have collected fossils from the low-relief exposures in this relatively small area. Articulated dinosaur skeletons, bonebeds comprising dinosaurs and vertebrate microfossils, nests of dinosaur eggs, invertebrate shell beds and trace fossils have been found. Nevertheless, most of the Iren Dabasu collections have not been prepared or described and the geology of this site has remained unstudied. Thus, the fossil assemblages and depositional environments have remained poorly known and somewhat enigmatic.The Sino-Canadian expeditions of 1988 and 1990 rekindled an interest in this formation and new results from these and previous expeditions are presented here. The fossil assemblage is close to that of the Bayn Shire Formation of Mongolia, but the generally accepted Cenomanian designation may be too old. The Iren Dabasu Formation comprises the remains of a low-sinuosity braided fluvial system that flowed toward the north-west and was deposited in a semiarid climate. Channels were broad (up to 1 km wide) and relatively shallow (less than 4 m deep). The floodplain was the site of frequent and energetic overbank flooding and early stages of soil formation. Although ephemeral floodbasin lakes and playas—resulting from overbank flooding—existed from time to time, there is no sedimentological or palaeontological evidence for laterally extensive and long term lacustrine environments as suggested by previous workers.