American Museum of Natural History 2003 ISSN 0003-0082
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3420, 19 pp., 12 ﬁgures, 1 table October 29, 2003
An Early Ostrich Dinosaur and Implications for
MARK A. NORELL,
PETER J. MAKOVICKY,
AND CHONGXI YUAN
A new ornithomimosaur from the Yixian Formation of Liaoning Province People’s Republic
of China is described. These beds are near the Jurassic-Cretaceous boundary. This specimen
is interesting because it has several primitive characters for ornithomimosaurs such as teeth
and a short ﬁrst metacarpal. This taxon is placed in a phylogenetic analysis of Coelurosauria
and shown to be near the base of the ornithomimosaur clade. Using this phylogeny we com-
ment on the biogeographic history of this group.
Spectacular fossils from China’s Liaoning
Province have become commonplace in the
last few years (Ji and Ji, 1996; Ji et al., 1999;
Hou, 1997; Gao et al., 2000). However, most
of these are nearly two-dimensional fossils
found in paper shales that represent ancient
pond and lake deposits. Although beautiful
Department of Earth Sciences, Nanjing University, 22 Hankou Road, Nanjing 210093, and Institute of Geology,
Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037 China. e-mail: firstname.lastname@example.org
Division of Paleontology, American Museum of Natural History. e-mail: email@example.com
The Field Museum, 1400 S. Lake Shore Drive, Chicago IL, 60660. e-mail: pmakovicky@ﬁeldmuseum.org
School of Earth and Space Sciences, Peking University, Beijing 100871, China. e-mail: firstname.lastname@example.org.
China University of Geosciences, Beijing 100083, China.
and often preserving soft-part anatomy, these
fossils can be frustrating because of a lack of
three-dimensional preservation. Furthermore,
theropod remains from Liaoning only in-
clude the maniraptoran groups Dromaeosaur-
idae (Xu et al., 1999b, 2000), Oviraptorosau-
ria (Ji et al., 1998, Xu et al., 2002a), Troo-
dontidae (Xu et al., 2002b), and Segnosaur-
idae (Xu et al., 1999a) and the more
2 NO. 3420AMERICAN MUSEUM NOVITATES
primitive compsognathid Sinosauropteryx
(Chen et al., 1998). Here we describe a new
ornithomimid dinosaur, the ﬁrst from the
Liaoning beds, and comment on its relation-
ships to other ornithomimids.
Ornithomimid dinosaurs were the ﬁrst
toothless nonavian dinosaurs to be described
(Marsh, 1890). Consequently, much has been
written concerning their relationships and
diet (Gauthier, 1986; Holtz, 1994; Sereno,
1997, Kobayashi et al., 1999; Norell et al.,
2001b). Although toothed forms have been
recovered (Pe´rez-Moreno et al., 1994; Bars-
bold and Perle, 1984), these are either difﬁ-
cult to place phylogenetically or are extreme-
Local farmers collected the specimen, and
some of the elements were clearly lost during
the excavation process. It is apparent that
both the tail and the forelimbs were present
in adjoining blocks (ﬁg. 1). When the spec-
imen was collected it was cracked into two
blocks, shattering many bones and leaving
parts of the skeleton in each block. During
the preparation process parts of the counter
block were glued to the main slab, and the
sediment surrounding the bones was re-
moved. In other cases individual elements
were prepared completely free of the counter
slab and afﬁxed to the main slab. This prep-
aration process resulted in a single block
with the specimen preserved in bas-relief
AMNH American Museum of Natural History
IGM Institute of Geology Mongolia
NGMC National Geological Museum of China
ROM Royal Ontario Museum
THEROPODA MARSH, 1881
COELUROSAURIA VON HUENE, 1914
ORNITHOMIMOSAURIA BARSBOLD, 1976
ORNITHOMIMINAE SERENO, 1998
Shenzhousaurus orientalis, new taxon
: NGMC (National Geolog-
ical Museum of China) 97-4-002.
: A partial skeleton preserved on
a sandstone block in a death pose with its
head above the torso. The distal hindlimbs,
distal tail, and the forelimbs (except for part
of the right hand) and the pectoral girdle are
missing. The head is crushed, exposing the
left side obliquely.
:Shenzhou is the ancient name
of China, orientalis refers to the east.
: Sihetun fossil site, Bei-
piao, Western Liaoning, China (ﬁg. 3).
: The holotype
comes from the lowermost, ﬂuvial part of the
Early Cretaceous Yixian Formation. These
rocks are older than 128 mybp and younger
than 139 mybp (Swisher et al., 2002); older
dates have been reported (Lo et al., 1999).
: an ornithomimosaur distin-
guishable from all others except Harpymimus
in having teeth restricted to the anterior den-
tary. Shenzhousaurus orientalis shows prim-
itive characters not found in advanced orni-
thomimosaurs, like a straight ischium and a
postacetabular process that is gently curved
rather than truncated. Shenzhousaurus orien-
talis is distinguishable from Pelecanimimus
by the tooth distribution pattern and the
primitive conﬁguration of the hand where
digit I is shorter than digits II and III.
The left side of the snout is well pre-
served, whereas the right side is crushed and
displaced postmortem (ﬁg. 4). The orbital
and braincase regions are ﬂattened and the
left frontal and parietal are ﬂipped under the
right. The left squamosal is isolated and lies
adjacent to the caudal end of the lower jaw.
The left mandible appears to be intact and
The premaxilla has a relatively short body,
and the premaxillary buccal margin is only
as long as the external naris. The internarial
bar is dorsoventrally ﬂat and is formed main-
ly by the premaxillae, with only a minor con-
tribution from the nasals. The posterodorsal
process of the premaxilla is elongate as in
other ornithomimids, and it overlaps the na-
somaxillary suture well posterior to the cau-
dal end of the naris. It is broadest at its base
but tapers caudally. Although incomplete dis-
tally, it does not appear to have reached the
level of the antorbital fossa. The labial sur-
2003 3JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
Fig. 1. NGMC 97-4-002 before preparation.
4 NO. 3420AMERICAN MUSEUM NOVITATES
Fig. 2. The holotype skeleton of Shenzhousaurus orientalis as preserved on the main block, with
parts in counterblock reattached. Abbreviations: g, gastralia; ga, gastroliths; lf, left femur; li, left ilium;
lis, left ischium; lp, left pubis; lu, ungual of left hand; pb, pubic boot; r-dI, right digit I; r-dII, right digit
II; r-dIII, right digit III; rf, right femur; rp, right pubis.
2003 5JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
Fig. 3. The fossil locality.
Fig. 4. Close-up of the left side of the skull of Shenzhousaurus orientalis. Abbreviations: ch, choana;
fr, frontal; ld, left dentary; ll, left lacrimal; lmx, left maxilla; ln, left nasal; lpmx, left premaxilla; lsq,
left squamosal; mxf, maxillary fenestra; plr, palatine recess; rn, right nasal.
face of the subnarial part of the premaxilla
is marked by a few neurovascular foramina,
the largest of which is located at the base of
the internarial bar.
The maxilla is very elongate and bears a
large antorbital fossa that is perforated by a
larger antorbital and a smaller accessory fe-
nestra. The rostral 40% of the maxilla lies
anterior to the antorbital fenestra and has a
ﬂat lateral surface marked only by a few fo-
ramina, presumably for neurovascular trans-
mission. The buccal margin is slightly sinu-
ous in this region and rises gently toward the
front. The buccal margin of the maxilla is
very shallow beneath the antorbital fossa. A
large maxillary palatal shelf is visible along
the anterior two-thirds of the antorbital fossa.
The fossa appears to be bordered by the nasal
for a short stretch dorsal to the antorbital fe-
nestra, although the maxilla is not complete
in this region. Posterior to this the dorsal
edge of the antorbital fenestra is bordered by
the elongate anterior ramus of the lacrimal.
The accessory fenestra perforates a de-
pressed medial lamina of the maxilla that
walls off the anterior third of the antorbital
fossa medially. The posterior part of this
lamina, which forms the interfenestral bar,
bears dorsal and ventral embayments along
the posterior border, perhaps indicating some
type of interfenestral connection as in troo-
dontids (Norell et al., 2000; Makovicky et
The jugal is poorly preserved, and articu-
lar contacts with the maxilla and lacrimal
6 NO. 3420AMERICAN MUSEUM NOVITATES
cannot be traced. The orbital portion of the
jugal is very slender, and the anteroventral
corner of the orbit appears to have had a
right-angled rather than a rounded shape.
Posteriorly, the jugal is obscured by other el-
The lacrimal bears an elongate anterior
process that borders the caudal half of the
antorbital fenestra dorsally. A short, pointed
posterior process is present on the lacrimal.
It may have inserted into a notch on the dor-
sal surface of the prefrontal as in Gallimi-
mus, but the prefrontal cannot be identiﬁed.
Neither large fossae nor hornlike structures
are present on the lacrimal.
A short section of the right postorbital is
exposed in dorsal view, and it forms the an-
terior part of the intertemporal bar. It is rel-
atively massive compared to the postorbital
contribution to the intertemporal bar in other
ornithomimid taxa. The postorbital of Shen-
zhousaurus orientalis does not reveal the
characteristic anterodorsal curvature seen in
The right frontal is exposed in dorsal view
(ﬁg. 5). A coronally directed crack extending
through the frontal just anterior to the artic-
ulation of the postorbital may be the result
of dorsoventral crushing of a strongly ﬂexed
part of the frontal. The frontals of other or-
nithomimid taxa are domed near the poste-
rior part of the orbit, forming a ﬂexure be-
tween the ﬂat parts of the frontal and parie-
tals. Anterior to the extensive orbital rim, the
lateral edge of the frontal is sinuous and the
medially inﬂected portion may mark a de-
pression for the reception of a prefrontal.
The parietals appear paired and unfused.
The dorsal surface of the parietal is ﬂat and
lacks a sagittal crest. A laterally concave
ﬂexure marks the medial edge of the supra-
temporal fenestra and separates the dorsal
surface of the parietal from the lateral surface
that forms parts of the adductor chamber. The
frontoparietal suture is sinuous in dorsal
view, as in Gallimimus (Osmo´lska et al.,
The left squamosal is disarticulated and
lies adjacent to the caudal end of the left
mandible. It is exposed in lateral view, and
the proximal end of the quadrate is preserved
in articulation with the squamosal. The squa-
mosal is tetraradiate, with two processes ex-
tending anteriorly around the caudal end of
the supratemporal fenestra, a rostroventrally
directed quadrate process that adheres to the
anterior edge of the quadrate shaft, and a
short lateral process. The intertemporal pro-
cess of the squamosal is longer than the me-
dial supratemporal process. The dorsal sur-
face of the squamosal between these two pro-
cesses is incised by a caudal extension of the
supratemporal fenestra, bordered by a sharp
rim, as in Gallimimus (IGM 100/1133). The
quadrate process of the squamosal is trian-
gular. The posterolateral process extends pos-
terior to the quadrate articulation, but its
length cannot be determined because it is
overlapped by a disarticulated piece of the
braincase. The articulation with the quadrate
is not exposed in lateral view in Shenzhou-
(IGM 100/1133) and Ornithomimus.
Parts of the palate, including parts of both
palatines and possibly the left pterygoid, are
exposed. The palatine bears two anteriorly
elongate processes that almost enclose the in-
ternal choana. The medial, interchoanal pro-
cess is longer than the lateral one, in contrast
to Allosaurus (Madsen, 1976), but similar to
Sinraptor (Currie and Zhao, 1993) and Dei-
nonychus (Witmer, 1997), and it extends at
least as far rostrally as the interfenestral bar.
The interchoanal process of the left side rises
dorsomedially to meet its counterpart on the
right side and form the interchoanal bar, pos-
sibly with participation of the pterygoids.
The interchoanal bar is unlike the large, lo-
bate structure of Allosaurus (Madsen, 1976),
but is more slender and curves anteriorly
from the posterior end of the choana as in
Velociraptor (Barsbold and Osmo´lska,
1999). The dorsal surface of the palatine
bears a deep fossa, the palatine recess (Wit-
mer, 1995), near the base of the maxillary
process just rostral to the level of the lacrimal
(ﬁg. 5). The palatine recess in Shenzhousau-
rus orientalis is in a similar position to pal-
atine recesses observed in dromaeosaurs
such as Deinonychus (Witmer, 1995: ﬁg. 32)
and Velociraptor (IGM 100/982). The recess
invades the palatine body mediodorsally in
Shenzhousaurus orientalis rather than poster-
odorsally as in the two dromaeosaurid taxa.
Part of the pterygoid process of the palatine
2003 7JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
Fig. 5. Closeup of braincase. Abbreviations: dv, dorsal vertebra; f, frontal; lp, left prootic, ls?, left
laterosphenoid, lsa, left surangular, lsq, left squamosal; r, rib.
is exposed within the orbit, posterior to the
The hooked jugal process is the only vis-
ible part of the ectopterygoid and is exposed
within the orbit slightly posterior to the pter-
ygoid process of the palatine. A narrow sliv-
er of bone dorsal to the jugal process of the
ectopterygoid to this may represent a part of
A large, crushed bone that overlaps the
posterior part of the mandible may be a la-
terosphenoid. We interpret a large broken el-
ement posterior to the right parietal as the left
prootic with its anterior surface (laterosphen-
8 NO. 3420AMERICAN MUSEUM NOVITATES
Fig. 6. The dentition of Shenzhousaurus orientalis as preserved in the left dentary.
oid articulation) facing upward (ﬁg. 5). A
well-delimited depression on the lateral sur-
face appears to be the dorsal tympanic recess.
Medial to it, the posterior border of the ﬂoc-
cular recess is visible. Part of the border of
a large foramen, which is surrounded by a
wide fossa on the lateral surface of the brain-
case, is visible anteroventral to the ﬂoccular
recess and is here interpreted as the exit for
the trigeminal nerve.
The complete left mandible is preserved,
but much of the postdentary region is cov-
ered by the unidentiﬁable braincase element.
The dentary is elongate but shallow and
spans about two-thirds the length of the jaw.
The dentary is deepest below the middle of
the antorbital fenestra. It tapers gently rostral
to this point, up to a point just posterior to
the toothrow, where it deﬂects rostroventral-
ly. The buccal margin is deﬂected anteroven-
trally at the symphysis, as in other ornithom-
imosaurs except Pelecanimimus (Pe´rez-Mo-
reno et al., 1994). The lateral surface of the
dentary is pocked by three roughly linear
rows of neurovascular foramina (ﬁg. 6).
These extend posteriorly to the end of the
abbreviated toothrow. Farther caudally, a
shallow groove follows the dorsal margin of
the dentary until it reaches the rostrodorsal
process of the surangular.
As in other ornithomimosaurs, the external
mandibular fenestra is reduced. It is bordered
dorsally by the surangular that has a long,
splintlike process overlapping the dentary.
Fragments of the angular are exposed along
the ventral border of the external mandibular
fenestra. The glenoid and retroarticular pro-
cess are exposed. A ﬂattened area just rostral
to the glenoid may correspond to the dorsal
trough or sulcus seen on the surangular of
many theropods, including Velociraptor,Ty-
rannosaurus, and Ornitholestes. As in other
ornithomimids, an everted tab forms the an-
terolateral margin of the glenoid. In these
taxa, such as Gallimimus, this tab articulates
with an elongate, curved extension of the lat-
eral quadrate condyle. The retroarticular pro-
cess is crushed, but it appears to be expanded
Six minute tooth crowns and a broken root
are preserved at the deﬂected anterior tip of
the left dentary. Gaps between the preserved
teeth suggest the presence of one or two ad-
ditional tooth positions. The teeth are conical
and project slightly anteriorly. They do not
have a constriction between the root and
crown. A thin layer of enamel is preserved
on the teeth. There is no trace of either ca-
rinae or serrations.
No cervical vertebrae can be identiﬁed on
2003 9JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
Fig. 7. Dorsal vertebrae of Shenzhousaurus
An articulated series of the last eight dor-
sal vertebrae are preserved in articulation
with the sacrum. The centra are elongate and
spool-shaped and are devoid of pneumatic
foramina (ﬁg. 7). The anteriormost centrum,
which is broken anteriorly, bears a faint keel
ventrally. Neural arches bear large pneumatic
and infrapostzygapophyseal fossae below the
transverse processes. The infraprezygapo-
physeal fossae are especially large and ap-
pear to extend into the prezygapophyses. The
neural spines are long, tall anteroposteriorly
expanded distally. The neurocentral sutures
are fused but not obliterated. In no case is a
neural arch separated from its corresponding
Parts of 10 dorsal ribs are preserved on the
block, but none is complete. Two left ribs,
which probably articulated with the fourth
and ﬁfth dorsals in the preserved series, have
anteroposteriorly ﬂared shafts as in other or-
nithomimids (Barsbold and Osmo´lska,
Parts of ﬁve sacral vertebrae are exposed
but are partly obscured by the pelvic ele-
ments and the left femur. The centra appear
to be fused, but the sutural lines are still ev-
ident. A constricted pit is visible on the ex-
posed lateral surface of both the third and
fourth sacrals. Such noninvasive depressions
are also present on the sacral vertebrae of
other ornithomimid taxa, including Orni-
thomimus (Makovicky, 1995), Gallimimus
(Osmo´lska et al., 1972), Struthiomimus, and
Archaeornithomimus (Makovicky, 1995).
The ilium appears to be slightly displaced
from the sacrum, thus exposing the trans-
verse processes of the last sacral in lateral
view. As in other ornithomimosaurs, the
transverse processes of this element ﬂare
widely distally where they meet the medial
border of the brevis fossa, and they may have
contributed to the insertion area of the cau-
difemoralis brevis musculature. The neural
spine of the last sacral appears to have been
freestanding, but it cannot be determined
whether the neural spines of the remaining
sacrals formed a lamina as in some other or-
A section of the tail comprising 15 artic-
ulated caudal vertebrae is preserved, curving
posterodorsally from the sacrum (ﬁg. 8). All
the preserved caudals possess transverse pro-
cesses or traces thereof, indicating that the
transition point lies distal to the preserved
section of the tail. Centrum length increases
distally in the preserved section, whereas
centrum height decreases distally.
The transverse processes are distally ex-
panded and backswept. Their distal ends are
rounded. In the second and third caudal ver-
tebrae, a thin lamina extends anteriorly from
the transverse process on to the lateral face
of the prezygapophysis, where it forms a dis-
tinct ridge bounding a shallow fossa. This
connection between the transverse process
and prezygapophysis is also present in Or-
nithomimus. The neural spines of the ﬁrst 12
vertebrae are obscured by transverse pro-
cesses. Those of the remaining three caudals
are parallelogram-shaped and lean posteri-
orly, extending beyond the caudal end of
their respective centra.
The ﬁrst chevron is situated between the
ﬁrst and second caudals. It is rod-shaped, but
its length is indeterminate, as the second
chevron covers it distally. The second to
ﬁfths chevron are very elongate, slender, and
rod-shaped with a slight posterior curvature
that becomes more pronounced in more dis-
10 NO. 3420AMERICAN MUSEUM NOVITATES
Fig. 8. Anterior caudal vertebrae of Shenzhousaurus orientalis.
tal elements. Posterior to this, the chevrons
become progressively wider, mediolaterally
compressed, shorter, and more hooked. The
last two chevrons are strongly hooked and
end in a point distally.
Parts of eight gastral arches from the right
side are preserved, but only one preserves
both the complete medial and lateral seg-
ments (ﬁg. 9). The medial segment has an
expanded and dorsoventrally compressed
midline end. It tapers distally and is over-
lapped anteriorly by the lateral element. The
two elements are approximately equal in
length, unlike those of higher ornithomimids,
in which the medial elements are longer. The
dorsal ends of the rodlike lateral elements are
slightly expanded and curve dorsally. The
last gastral element is three times wider than
the preceding segments. The last gastral arch
may have only comprised this medial ele-
The pelvis is present in semiarticulation
although some elements were shattered when
the slab was split. The ilium is about equal
in length to the pubis, and the ischium is only
slightly shorter (see table 1).
Most of the exposed dorsal surface of the
ilium is shattered, as it lay on the contact
between the slab and counterslab (ﬁg. 10).
Nevertheless, it can be determined that the
anterior and posterior blades are roughly
equivalent in length and that the iliac blade
was dorsoventrally low. The ilia covered six
vertebrae, less than in Gallimimus and Or-
nithomimus (Barsbold and Osmo´lska, 1990).
Apparently the ilia met at the midline as in
other ornithomimids (Makovicky et al., in
2003 11JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
Fig. 9. Gastroliths of Shenzhousaurus orientalis. ga, gastroliths; ldIIIu, left digit 3 ungual; lf, left
femur; li, left ilium; rdI, right digit 3, rdII; right digit 2; rdIII, right digit 3.
press; Barsbold and Osmo´lska, 1990). Both
anterior and posterior blades also are round-
ed similar to the oviraptorosaur Khaan
mckennai (personal obs.). This is unlike the
condition in other ornithomimids where the
ilium is dolichoiliac and the posterior blade
is truncated rather than tapering to a point
(Barsbold and Osmo´lska 1990). Although the
anterior blade is hooked as in other orni-
thomimids, the hook is small as in Khaan
mckennai (personal obs.), Ornitholestes her-
manni (Osborn, 1903), and Velociraptor
mongoliensis (Norell and Makovicky, 1997,
1999). Posterior to the acetabulum the lateral
border of the brevis fossa is concave ven-
trally, giving it a slightly hooked appearance.
This is unlike the condition in other orni-
thomimids where the lateral margin of the
brevis fossa is straight (Barsbold and Os-
mo´lska 1990). The preacetabular apron is
slightly concave and is separated from the
main body of the ilium by a sharp ridge that
continues anteriorly to form the lateral bor-
der of the deep cupedicus fossa. The acetab-
ulum is marked by a large supra-acetabular
crest that overhangs the acetabulum. As is
typical of ornithomimosaurs, the supracetab-
ular crest formed a hood or cap over the en-
tire proximal femur. The ischiac peduncle is
not wide, but is formed as a ventral conical
process, as in other ornithomimids and tyran-
nosaurs, which inserts into a slot in the is-
chium. A large antitrochanter is present. The
postacetabular apron is large and like the
preacetabular apron is separated from the il-
iac blade by a large ridge that continues pos-
12 NO. 3420AMERICAN MUSEUM NOVITATES
Measurements of Holotype of Shenzhousaurus orientalis (all measurements in millimeters)
teriorly to deﬁne the lateral edge of the brev-
is fossa. The brevis fossa is large and deep
and expands posteriorly as a deep trough to
the posterior limit of the ilium.
The left ischium is preserved in near ar-
ticulation with the ilium and can be observed
in lateral view. The iliac process is long and
is angled posterodorsally from the shaft. On
its posteroproximal lateral surface is a large
triangular scar as in other ornithomimosaurs
and tyrannosaurs (Buffetaut et al., 1996). The
surface of the acetabulum that lies in be-
tween the iliac and pubic processes is smooth
and crescent-shaped. The pubic process is
short, relatively shorter than in other orni-
thomimids. In fact, the pubic contact lies
along the same axis as the shaft of the ischi-
um. Just ventral to the pubic contact lies a
large hook-shaped obturator process. It is
possible that this process may have com-
pletely enclosed a foramen; however, break-
age in this area prevents conﬁrmation. Dis-
tally the ischium tapers and then expands on
its distal end into a small triangular boot that
The left pubis and part of the right are ex-
posed laterally and are in near articulation
with the ilia and ischia. The overlying femur
obscures most of its proximal features. How-
ever, the articulation with the ilium indicates
that it was propubic. Near the iliac contact
the pubis is ﬂat, becoming thin and rodlike
distally. It is slightly anteriorly convex, and
laterally it is marked by a small sinuous lon-
gitudinal ridge or crest which extends nearly
half the length of the shaft. This crest divides
2003 13JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
Fig. 10. Pelvis of Shenzhousaurus orientalis. Abbreviations: ct, ectocondylar tuber; ft, fourth tro-
chanter; gp, gastrocnemius process; gt, greater trochanter; lc, lateral crest; lf, left femur; lp, left pubis;
li, left ilium; lis, left ischium; lt, lesser trochanter; mc, medial crest; o, obturator foramen; pb, pubic
boot; rf, right femur, rp, right pubis; sac, sacrum.
14 NO. 3420AMERICAN MUSEUM NOVITATES
Fig. 11. Manus of Shenzhousaurus orientalis. ga, gastroliths; ldIIIu, left digit 3 ungual; rmcII, right
metacarpal 2; rmcIII, right metacarpal 3; rpII-1, right digit 2 ﬁrst phalanx; rpII-2, right digit 2 second
phalanx; rpIII-1, right digit 3 ﬁrst phalanx; rpIII-2, right digit 3 second phalanx; rpIII-3, right digit 3
third phalanx, rdIu, right digit 1 ungual; rdIIu, right digit 2 ungual; rdIIIu, right digit 3 ungual.
the pubis into anterior, and posterior-facing
surfaces. Medially the pubic moietes meet to
form the pubic apron, which is extensive,
forming nearly two-thirds the length of the
pubis. The pubic apron is posteriorly concave
and is formed from crests that emanate from
the anterior of the pubic shafts. Distally the
pubes form a large pubic boot. At the ter-
minus of the pubes the pubic boot appears to
be transversally expanded. This boot is mod-
erately expanded anteriorly, where it forms a
pronounced point. Posteriorly the pubic boot
is much more extensive. Ventrally the pubic
boot is deeply convex, as opposed to the con-
dition in Gallimimus, where the ventral edge
of the boot is nearly straight.
Only parts of the right hand, including all
of digits II and III, and a single ungual of
the left hand are preserved (ﬁg. 11). The pre-
served elements of the right hand are in ar-
ticulation, but the hand is situated at the edge
of the block, and the missing parts were ob-
viously lost during collection when the block
was trimmed. The ungual and a partial im-
pression of the penultimate phalanx are the
only preserved parts of digit I. The ungual is
slightly curved, not trenchant, and has a
small ﬂexor tubercle situated distal to the
proximal articulation. A deep groove extends
along the medial surface of the ungual, to the
2003 15JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
distal end of the ungual. The preserved un-
gual of digit I of the left manus shows a sim-
ilar groove on the lateral surface, and these
two grooves are parallel along the ungual,
unlike the offset grooves on the unguals of
dromaeosaurs. As preserved, the ungual of
digit I does not reach the level of the prox-
imal end of the unguals of digits II and III.
Because the hand is articulated, the pre-
served position of ungual I-2 reﬂects the ac-
tual proportions of the digits in life and in-
dicates that digit I is proportionately shorter
than digits II or III, which is the primitive
condition for Tetanurae (Gauthier, 1986; Ser-
eno, 1997). Among ornithomimosaurs, the
condition in Shenzhousaurus appears most
like that of Harpymimus (Barsbold and Perle,
1984), in which digit I is short. The unguals
are slightly curved, not trenchant, and bear
small ﬂexor tubercles distal to the proximal
articulations as in other ornithomimosaurs
(Osmo´lska, 1997; Sereno, 2001). In Galli-
mimus (Osmo´lska et al., 1972), Struthiomi-
mus (Osborn, 1917; Nicholls and Russell,
1985; AMNH 5339), Anserimimus (IGM
100/300), Pelecanimimus (Pe´rez-Moreno et
al., 1994), and Ornithomimus (Sternberg,
1933) the ungual of digit I reaches to at least
the base of the unguals of digits II and III.
Only the distal part of metacarpal II is pre-
served, and it is exposed in ventral and me-
dial views. The distal articulation is divided
into two distinct tubercles ventrally. A pro-
nounced ﬂexor pit separates the two tuber-
cles. Phalanx II-1 has a transversely ﬂat ven-
tral surface, with a pronounced arch in lateral
view. The proximal articulation is extensive,
and a small posteromedial lappet forms a
small heel extending ventral to the distal end
of the metacarpal. The distal articulation is
divided into two widely separated tubercles
in ventral view, and the articulation appears
ginglymous, although it is poorly preserved.
Phalanx II-2 is elongate, slender, and has
a nearly straight shaft that is oval in cross
section. The proximal articulation is formed
as a deep arc in lateral view, with dorsal and
ventral parts of the articulation projecting far
posteriorly. In contrast to Gallimimus, the
ventral end of the articulation extends farther
proximally than the dorsal tip. A small, mid-
line process or tuber is present on the ventral
surface of the phalanx II-2, adjacent to prox-
imal articulation. The apparently ginglymous
distal articulation describes an arc of approx-
and has a small, elliptical col-
lateral ligament pit. The ungual of digit II is
similar to that of digit I, except that is slight-
Metacarpal III is almost complete. It ap-
pears to be almost as thick as the preserved
part of metacarpal II, as in Harpymimus
(Barsbold and Osmo´lska, 1990). The proxi-
mal end is triangular in proximal view, with
a slightly concave area where it was apressed
against the shaft of metacarpal II. The shaft
of metacarpal III appears to curve slightly
laterally. The distal articulation divides into
two tubera ventrally.
Phalanx III-1 is short and blocky, with ﬂat
medial and ventral faces that are set perpen-
dicular to each other. As in phalanx II-1, the
medioventral end of the proximal articulation
extends for a short distance below the end of
metacarpal III. Distally, the medial collateral
ligament pit is very weak. The distal articu-
lation is apparently ginglymoid. Phalanx III-
2 is almost identical to phalanx III-1, except
for being more slender and lacking the short
heel on the proximal articulation. Phalanx
III-3 is longer than the combined lengths of
digits III-1 and III-2, as in derive ornithom-
imids (Barsbold and Osmo´lska, 1990). Prox-
imally, phalanx III-3 is similar to II-2, in-
cluding the presence of a small tubercle just
ventral to the proximal articulation. The shaft
thins distally and is thinnest just adjacent to
the distal articulation, which is offset ven-
trally from the shaft. The medial collateral
ligament fossa is deep but not displaced dor-
sally as in many other theropods. The ungual
is similar to those of digits I and II and is
roughly as long as that of digit II. It appears
to have a more pronounced groove for the
claw sheath than do the other unguals.
Both right and left femora are preserved;
however, the right is severely damaged (ﬁg.
10). The left femur lies in articulation with
the acetabulum, and proximal lateral and dis-
tal proximal surfaces are exposed. Hindlimb
elements distal to the femur are not pre-
As in other ornithomimids, the femur is
16 NO. 3420AMERICAN MUSEUM NOVITATES
Fig. 12. Strict consensus of 432 most parsimonious trees depicting relationships among ornithomi-
mosaur species derived from parsimony analysis of 220 characters in 50 coelurosaurian species (see
http://research.amnh.org/users/norell/index.html). Tree statistics for shortest trees are (TL
45, and RI
75). Continental distributions are listed after taxon names.
slightly bowed (contra Barsbold and Osmo´l-
ska, 1990), but not to the level of Manirap-
tora. The proximal end is exposed in lateral
view. The greater trochanter is higher than
the lesser trochanter. The lesser trochanter is
alariform and is separated from the greater
trochanter by a deep cleft that extends ap-
proximately 28 mm down the femoral shaft.
This cleft ends in the bump, which appar-
ently does not continue down the femoral
shaft as the lateral ridge as in maniraptori-
forms like Velociraptor (Norell and Makov-
icky, 1997, 1999). A small ridge divides the
lesser trochanter into anterior and posteriorly
oriented surfaces. A weakly developed fourth
trochanter lies distal and medial to the pos-
terior trochanter. Distally the femur istwisted
to expose the posterior surface. The medial
condyle is much larger than the lateral one,
is bulbous, and extends medial to the axis of
the femoral shaft. A thin crest, or buttress,
extends proximally up the shaft of the femur
from the medial condyle. The medial and lat-
eral condyles are separated by a deep wide
popliteal fossa that is not closed distally by
lateral or medial expansions. The gastrocne-
mius process that lies posterior to the lateral
condyle is unusual in that it is thin and its
lateral surface is nearly ﬂat. It contacts the
shaft of the femur nearly at a right angle and
borders a ﬂat, triangular surface on the fem-
oral shaft that extends to the edge of the lat-
eral condylar surface. A very low ectocon-
dylar tuber is also present at the lateral apex
of the lateral condyle.
The thoracic cavity of Shenzhousaurus or-
ientalis contains numerous pebbles, which
are best interpreted as gastroliths. The uni-
form matrix surrounding the skeleton is de-
void of lithic clasts of a comparative size.
The pebbles are distributed unevenly in the
thoracic cavity, with a concentration just an-
terior to the preserved part of the gastral bas-
ket. Less concentrated amounts of gastroliths
occur throughout the rest of the thoracic cav-
ity, and some are dispersed posteriorlyacross
the femur and proximal end of the left ischi-
um and sacrum. The gastroliths are hetero-
geneous in size, shape, and composition.
Whereas some are smooth and rounded, oth-
ers are highly angular and/or pockmarked.
Gastroliths have been previously reported in
ornithomimosaurs (Kobayashi et al., 1999).
Phylogenetic analysis posits Shenzhousau-
rus near the base of Ornithomimosauria (Ma-
kovicky et al., in press), being more ad-
vanced than the Barremian Pelecanimimus
(ﬁg. 12). Ornithomimosaurs are monophylet-
ic and are the sister group to a clade com-
posed of Maniraptora (including Ornitholes-
tes) (Gauthier, 1986; Sereno, 1997; Xu et al.,
2003 17JI ET AL.: A TOOTHED ORNITHOMIMOSAUR
2002b). No support was found for a close
relationship between ornithomimosaurs and
troodontids (Holtz, 1994). Alvarezsaurids,
which have been postulated as close orni-
thomimosaur relatives (Sereno, 2001), are
found to be the sister group of all other Man-
iraptora except Ornitholestes.Shenzhousau-
rus and other ornithomimosaurs are more de-
rived than Pelecanimimus in the progressive
loss of teeth from the upper jaws and all but
the tip of the dentary (Shenzhousaurus,Har-
pymimus) or complete loss of teeth (higher
ornithomimosaurs). Harpymimus and Shen-
zhousaurus are similar in having primitive
manual proportions in which metacarpal I is
much shorter than either II or III, but Har-
pymimus shares a derived curvature of the
ischium with higher ornithomimids.
Except for the Spanish taxon Pelecanimi-
mus, most ornithomimids are known from
Central Asia and western North America.
Examining distributions within the context of
the phylogeny (ﬁg. 12) demonstrates that ear-
ly ornithomimids have an extensive evolu-
tionary history in eastern Asia, yet the center
of origin is ambiguous because of the Euro-
pean range of Pelecanimimus. Several other
dinosaur clades, including tyrannosaurs (Hutt
et al., 2001) and pachycephalosaurs (Sereno,
1999), whose derived members are mainly
known from Asia and North America, also
have basal taxa from the Early Cretaceous of
Europe predating the formation of the Turgai
Straits. Among higher ornithomimosaurs, a
single dispersal across Beringia is required to
account for the distribution of taxa between
North America and Asia if North American
ornithomimids form a monophyletic taxon.
Otherwise, two dispersals are required to ex-
plain the known geographic diversity of this
Advanced ornithomimosaurs lack teeth
and had beaks (Osborn, 1917, Norell et al.,
2001b). The edentulous nature of their beaks
has been used along with gastroliths (Kobay-
ashi et al., 1999) to suggest that the diet was
highly specialized. According to our phylo-
genetic analysis, the advanced ornithomimid
condition progressed through stages of loss
of the upper and posterior dentary teeth ini-
tially as seen in the reduced maxillary tooth-
row in the basal form Pelecanimimus.Shen-
zhousaurus and Harpymimus illustrate a
more progressive state in which maxillary
teeth are absent and the dentary only bears
teeth near the symphysis.
Although tooth loss is common among
coelurosaurs (Chiappe et al., 1999), the pat-
tern is disparate among groups. Therizino-
sauroids and hesperornithiformes have eden-
tulous premaxillae, but retain maxillary and
dentary teeth. Although advanced ovirapto-
rosaurs are edentulous, the basal Caudipteryx
has teeth restricted to the premaxilla. Nev-
ertheless, the ornithomimosaur pattern where
the lower jaw is toothed anteriorly and the
entire upper jaw is edentulous appears
unique as a phylogenetic precursor to tooth-
lessness among theropod dinosaurs, with the
possible exception of the basal avialan Shen-
zhouraptor (Ji et al., 2002b and 2003, Zhou
and Zhang, 2002).
We thank the National Geological Muse-
um of China. Mick Ellison prepared the il-
lustrations, and Brian Roach prepared the
specimen with the consultation of Marilyn
Fox. The Division of Paleontology at the
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