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Deinonychosaurian theropods, the dinosaurian sister group of birds, are characterized by a large raptorial claw borne on a highly modified second digit that was thought to be held in a retracted position during locomotion. In this study, we present new trackway evidence for two coeval deinonychosaurian taxa from the Early Cretaceous of Shandong, China that indicate a hitherto unrecognized body size diversity for this period and continent. These fossil tracks confirm diversity and locomotory patterns implied by phylogeny and biogeography, but not yet manifested in the body fossil record. Multiple parallel and closely spaced trackways generated by the larger track maker provide the best evidence yet discovered for gregarious behavior in deinonychosaurian theropods.
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ORIGINAL PAPER
Behavioral and faunal implications of Early Cretaceous
deinonychosaur trackways from China
Rihui Li &Martin G. Lockley &Peter J. Makovicky &
Masaki Matsukawa &Mark A. Norell &
Jerald D. Harris &Mingwei Liu
Received: 1 June 2007 /Revised: 30 August 2007 / Accepted: 3 September 2007
#Springer-Verlag 2007
Abstract Deinonychosaurian theropods, the dinosaurian
sister group of birds, are characterized by a large raptorial
claw borne on a highly modified second digit that was
thought to be held in a retracted position during locomotion.
In this study, we present new trackway evidence for two
coeval deinonychosaurian taxa from the Early Cretaceous of
Shandong, China that indicate a hitherto unrecognized body
size diversity for this period and continent. These fossil
tracks confirm diversity and locomotory patterns implied by
phylogeny and biogeography, but not yet manifested in the
body fossil record. Multiple parallel and closely spaced
trackways generated by the larger track maker provide the
best evidence yet discovered for gregarious behavior in
deinonychosaurian theropods.
Keywords Deinonychosaur .Cretaceous .Footprint .
Gregariousness .China .Locomotion
Introduction
Deinonychosaurian theropod dinosaurs, such as Troodon,
Velociraptor, and Microraptor, have long sustained both
popular and scientific interest for numerous reasons,
including their close phylogenetic relationship to birds
(Makovicky and Norell 2004) and the unusual structure
(Currie and Dong 2001; Norell and Makovicky 1997;
Ostrom 1969; Xu and Norell 2004) and use (Barsbold
1998; Carpenter 1998) of their sickle-clawed feet. But
despite these studies, little direct evidence yet bears on
issues of the in vivo morphology of the feet of these dino-
saurs (Lockley et al. 2004; Zhen et al. 1994) and how they
were maintained during locomotory behavior. Similarly,
deinonychosaurs have often been portrayed as gregarious
(e.g., Ostrom 1990), although evidence presented in support
of this is ambiguous. In this study, we report the discovery
of multiple trackways of both a large and a small species of
Naturwissenschaften
DOI 10.1007/s00114-007-0310-7
Communicated by: G. Mayr
The online version of this article (doi:10.1007/s00114-007-0310-7)
contains supplementary material, which is available to authorized
users.
R. Li
Qingdao Institute of Marine Geology, China Geological Survey,
Qingdao 266071, Peoples Republic of China
e-mail: rihuiliqd@yahoo.com.cn
M. G. Lockley (*)
Dinosaur Tracks Museum, University of Colorado at Denver,
Denver, Colorado 80217, USA
e-mail: Martin.Lockley@cudenver.edu
P. J. Makovicky
Department of Geology, Field Museum of Natural History,
Chicago, IL 60605, USA
e-mail: pmakovicky@fieldmuseum.org
M. Matsukawa
Department of Environmental Sciences,
Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
e-mail: matsukaw@u-gakugei.ac.jp
M. A. Norell
Department of Vertebrate Paleontology,
American Museum of Natural History,
New York, NY 10024, USA
e-mail: norell@amnh.org
J. D. Harris
Science Department, Dixie State College,
225 South 700 East, St. George, Utah 84770, USA
e-mail: jharris@dixie.edu
M. Liu
Fourth Geological and Mineral Resources Survey of Shandong,
Wei-fang 261021, Peoples Republic of China
Early Cretaceous deinonychosaur from Junan County,
Shandong Province, China. These trackways are extensive,
well preserved, and reveal excellent details of foot
morphology. In addition to confirming that the sickle claw
of digit II was held retracted during locomotion, the
presence of multiple parallel and closely spaced trackways
on a single bedding plane allow an analysis of gait and
provide strong evidence for gregarious behavior. When
combined with the small coeval dromaeosaurids known
from body fossils, these trackways increase the known
diversity of the Early Cretaceous, Asian deinonychosaurian
fauna to include taxa of substantially larger body size. The
presence of large deinonychosaurs in this fauna has been
predicted by phylogeny and biogeography but is not yet
documented by the body fossil record.
Materials and methods
The trackways occur in Lower Cretaceous rocks of the
Tianjialou Formation (Fig. 1) and form part of a rich
vertebrate ichnofauna of more than 300 tracks on 12
different stratigraphic levels pertaining to at least eight
named and unnamed ichnotaxa, including zygodactyl avian
Shandongornipes muxiai (Li et al. 2005a,b; Lockley et al.
2007b) and tiny Minisauripus (Lockley et al. 2007a)
theropod tracks. Among these tracks are 18 large (foot
length up to 28.5 cm) deinonychosaurian footprints (Table 1)
assigned to Dromaeopodus shandongensis ichnogen. et
ichnosp. nov., plus two smaller deinonychosaurian foot-
prints (foot length 10 cm) in a single trackway attributed
to the poorly known Velociraptorichnus sichuanensis (Zhen
et al. 1994) (Fig. 2). Because of its excellent fidelity and
diversity of unique or very rare tracks, such as Dromaeopodus,
Velociraptorichnus, and Shandongornipes, this locality, still
under investigation, is one of the most important and most
diverse ichnological sites in Asia.
All originals of tracks and trackways discussed herein
remain in situ at Houzuoshan Dinosaur Park. Measurements
and tracings were taken directly from the track surfaces.
Molds were also made from these surfaces that were later used
to generate the holotype and paratype casts discussed below.
Description of specimens
Ichnotaxonomy
Dromaeopodidae ichnofam. nov.
Type ichnogenus and ichnospecies
Dromaeopodus shandongensis ichnogen. et ichnosp. nov.
Fig. 1 Occurrences of deinonychosaur tracks. aDidactyl deinony-
chosaur tracks have been reported from three Cretaceous dinosaur
tracks sites in East Asia: Junan (this paper), Emei (Zhen et al. 1994),
and Yanguoxia (Li et al. 2006). By comparison, the large number of
Asian, Cretaceous dinosaur tracksites underscores the scarcity of
deinonychosaurian tracks. bStratigraphic occurrence of deinonychosau-
rian tracks within the Tianjialou Fm. at Junan; empty spaces represent
covered intervals. The section is composed of sandstone beds deposited
in river channels and intervening mudstones deposited in floodplain
environments. Dinosaur tracks, including those referred to the Dro-
maeopodidae, occur in thin mud layers draped on thicker sandstone
beds, indicating they were impressed shortly after flooding events
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Diagnosis
Narrow, didactyl tracks of a biped with digit III only
slightly longer than IV, and digit II represented by a short,
round impression posteromedial to free part of digit III.
Known distribution
Early Cretaceous of eastern Asia and western North
America.
Referred ichnotaxa
Velociraptorichnus sichuanensis (Zhen et al. 1994) and
Dromaeopodus shandongensis ichnogen. et ichnosp. nov.
Dromaeopodus shandongensis ichnogen. et ichnosp. nov.
Etymology
From the Greek dromaeus,runner,and pous,foot,
referring to probable taxonomic affinities of track maker.
The specific epithet refers to the holotype locality in
Shandong Province.
Holotype and paratype
The holotype is a University of Colorado at Denver (CU)
replica of a trackway consisting of four footprints (CU
214.111) (Fig. 2e; Table 1: trackway 7). The paratype is CU
214.112, replica of a left pes (Table 1: trackway 8). The
original tracks and trackways remain in the field.
Horizon and locality
BarremianAptian Tianjialou Formation, uppermost mem-
ber of the Dasheng Group, Houzuoshan Dinosaur Park,
Junan County, Shandong Province, China. The Tianjialou
Formation has been assigned an Early Cretaceous, and most
likely BarremianAptian, age based on its fossils of
Psittacosaurus spp. as well as conchostracans (Yanjiestheria
spp.) known to be of this age elsewhere in China (Li et al.
2005a).
Known distribution
Early Cretaceous of eastern Asia.
Diagnosis
Tracks made by a biped that are functionally didactyl, elon-
gate, and exhibit the following characteristics: digit III and
IV traces subparallel, subequal in length, displaying lat-
erally convex curvature, and possessing both three toe pads
each as well as sharp claw impressions; suboval heel pad
forming about one-third of the posterior length; proximal
portion of digit II impressed as a large, hemispherical
depression medial to the anterior margin of the heel pad
and posteromedial to the margin of digit III; step lengths
from 92103 cm in the three preserved trackways; pace
angulation high (170°; Fig. 3; Table 1); digit III axis shows
slight inward rotation (10°) relative to sagittal plane.
The curved digits of Dromaeopodus distinguish the
ichnotaxon from the smaller Velociraptorichnus, which
has straight digits. In both, though less prominently in
Velociraptorichnus, the proximal portion of digit II is
represented by a large hemispherical depression medial to
the anterior margin of the heel pad and posteromedial to the
margin of digit III (Fig. 2; Supplementary Movie S1). None
of the footprints are deep enough to have captured digit I or
metatarsus impressions (Gatesy et al. 1999).
Discussion
Foot morphology and track maker
Three features of Dromaeopodus tracks are consistent with
the anatomy of articulated deinonychosaur foot fossils to the
exclusion of those of any other bipedal Mesozoic taxon:
the abbreviated impression of digit II, indicating retraction
of its claw; the subequal lengths of digits III and IV; and
their nearly parallel orientation and slight inward curvature
(Currie and Dong 2001; Norell and Makovicky 1997;
Ostrom 1969; Xu and Norell 2004). Some basal birds (e.g.,
Rahonavis) may also have adopted a functionally didactyl
posture (but see Makovicky et al. (2005)), but are all far too
small to have made Dromaeopodus or Velociraptorichnus
tracks and no East Asian, Early Cretaceous candidates are
Table 1 Distribution of left and right footprints, pes length and width,
step and stride length, and pace angulation for eight trackways of D.
shandongensis
Trackway
number
Left/
right
prints
Pes
length
(cm)
Pes
width
(cm)
Step
length
(cm)
Stride
length
(cm)
Pace
angulation
1/1 28 12.5 – – –
2/1 (26) (12.5) – – –
3 1/(24) 12.5 – – –
4 1/– –
5 2/2 26 9.5 103 – –
6 3/2 26.5 12.5 103 – –
7 2/2 28.5 12.5 93 186 170°
8/1 – – – – –
Trackway 7 is the holotype (Fig. 2e). Values in parentheses are
estimates from incomplete tracks.
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known. The only other described didactyl archosaur tracks
are Late Triassic in age (Gaston et al. 2003) and otherwise
unique in toe pad morphology and thus both temporally and
anatomically incongruent with a deinonychosaurian origin.
A diverse assemblage of deinonychosaurs is known from
the Early Cretaceous of Asia (for reviews, see Makovicky
and Norell (2004); Norell and Xu (2005); Turner et al.
(2007)), further supporting our identification of the track
maker as a deinonychosaur. With the exception of the
original report of Velociraptorichnus from the Early
Cretaceous of Sichuan (Zhen et al. 1994), unnamed tracks
from South Korea (MGL, personal observation), and
unnamed ichnites of dubious quality from the Early Creta-
ceous of Utah (Lockley et al. 2004) and Gansu Province,
China (Li et al. 2006), confirmed deinonychosaurian tracks
have been notably absent from the ichnological record. The
identification of tracks that are quite unique in the track
record, and both anatomically and temporally consistent with
having been made by deinonychosaurians, warrants placing
Dromaeopodus shandongensis and Velociraptorichnus with-
in their own ichnofamily.
The Deinonychosauria comprises two clades, the Troodon-
tidae and Dromaeosauridae. Basal members of both lineages
are remarkably small animals (Makovicky et al. 2005; Xu and
Norell 2004; Xu et al. 2002), but large dromaeosaurids, with
body lengths in excess of 3 m, are known from the Early
Cretaceous of North America (Kirkland et al. 1993) and
from the early Late Cretaceous of Mongolia (Perle et al.
1999), whereas large bodied troodontids only occur in Cam-
panianMaastrichtian sediments on either continent, and even
then are not known to attain dimensions necessary to qualify as
potential Dromaeopodus track makers (Makovicky and
Norell 2004). Therefore, the Dromaeopodus track maker
was most parsimoniously a large dromaeosaurid as inferred
from both phylogenetic understanding of body size evolution
(Turner et al. 2007b) and consideration of geological age and
paleobiogeography.
Anatomical investigation of the hypertrophied second
digits of deinonychosaurs, with their expanded interphalan-
geal joints, led to the interpretation of these animals as
being functionally didactyl (Ostrom 1969). In many well-
preserved specimens of both dromaeosaurs and troodontids,
Fig. 3 Map of sedimentary bed
surface with six parallel and
closely spaced trackways of
Dromaeopodus indicating si-
multaneous passage of a struc-
tured group of at least six
similarly sized individuals. In-
dividual trackways are enumer-
ated (numbers beginning with
D) and directions of travel are
indicated by long arrows with
black heads. Current direction,
as determined by ripples on the
surface, is denoted by small
white arrow
Fig. 2 a Velociraptorichnus and ceDromaeopodus tracks from
Junan. The comparative schematic (b) illustrates the relative size and
anatomical differences between the smaller Velociraptorichnus (left)
and larger Dromaeopodus (right) prints. Close-ups of the middle right
(c) and left (d) prints, respectively, are from the holotype trackway
(e). Scale bars: a5 cm, c10 cm and e1 m
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the second pedal digit is indeed preserved in a retracted
position (Currie and Dong 2001; Norell and Makovicky
1997; Russell and Dong 1993), supporting the prediction
that footprints of these animals would only register a partial
impression of digit II (Ostrom 1969). Dromaeopodus and
Velociraptorichnus trackways, representing multiple indi-
viduals of two discreet taxa from different time horizons,
provide incontrovertible evidence that the large digit II claw
was consistently held in a retracted position, with only the
proximal part of digit II involved in weight-bearing during
locomotion.
Footprints often reveal anatomical features that cannot
be inferred from skeletal anatomy. The unexpectedly large,
hemispherical impression demonstrates that a toe pad
cushioned the basal part of digit II (Fig. 2) in the large
Dromaeopodus and, to a lesser extent, smaller Velocirap-
torichnus track makers at the Junan tracksites. A larger heel
pad cushioned the base of the foot below the metatarsal
digital articulations in Dromaeopodus. Such heel pads have
been observed in trackways of sauropods and other graviportal
dinosaurs, but are unusual in nonavian theropod tracks.
Moderately large heel pads and toe pads are observed in ratites
such as the emu (Dromaius) and cassowary (Casuarius).
Seriemas (Cariama spp.), which are mid-size South American
gruiformbirds with enlarged, trenchant claws on digit II
analogous to those of deinonychosaurs, also possess single,
remarkably large heel pads below their metatarsophalangeal
joints (Fig. 4).
Behavior
The Dromaeopodus sample resolves into eight trackways
from three stratigraphic levels (Figs. 1,2, and 3; Table 1).
The clear imprints of full foot lengths and the lack of toe
drag marks extending anterior to the footprints indicate that
all of the individuals that generated the trackways were
walking rather than running. Trackways 14 and 8 are
represented by isolated footprints of moderate depth (1
2 cm) displaying clear pad and claw impressions. Track-
ways 57 each represent 34 consecutive steps, allowing
for measurements of stride and pace angulation (Table 1).
Trackways 16 occur together on a single bedding plane
(Fig. 3); all are closely spaced and indicate an identical
direction of travel. The bedding plane, a thin layer of
sandstone (Fig. 3), is covered with an irregular mud drape
and ripple marks. The absence of desiccation cracks
indicates the footprints were emplaced within a very short
time span. The overlying sandstone layer also bears
footprints made by other dinosaurs running parallel, but
opposite, to the deinonychosaurian trackway directions,
suggesting that the tracks were emplaced parallel to a
physically controlledlandscape feature such as shoreline
or drainage that was subject to episodic flooding (Ostrom
1972). Current ripples preserved along with the Dromaeo-
podus tracks (Fig. 3) suggest that a water body or waterway
of some sort was indeed present; site sedimentology
suggests a river channel complex.
Dromaeosaurids have been portrayed as both solitary
and gregarious, and tracks provide a means of testing both
hypotheses by preserving evidence of living behavior.
Tenuous evidence previously advanced in support of
hypothesized gregarious behavior in dromaeosaurids has
consisted solely of taphonomic interpretation of four partial,
largely disarticulated skeletons of Deinonychus alongside a
skeleton of the ornithopod Tenontosaurus and the occur-
rence of more shed Deinonychus teeth at one Tenontosau-
rus carcass than could be expected from a single individual
(Maxwell and Ostrom 1995; Ostrom 1969,1990). Such
discoveries could also result from distinct, time-averaged
death or scavenging events, however, and are subject to
alternative interpretations, such as chance occurrence of an
opportunistic feeding frenzy (Brinkman et al. 1998),
perhaps with agonistic behavior between individuals com-
peting for limited resources (Roach and Brinkman 2007).
The discovery of six parallel, closely spaced D. shan-
dongensis trackways provides compelling, independent evi-
dence for at least occasional gregarious (packor family
group) behavior in the track-making animals, comparable to
what has been demonstrated in other dinosaurs (Lockley
1989; Ostrom 1972). The tracks do not overlap, footprint
size is almost uniform between trackways, and inter-
trackwayspacing (Lockley 1989) is regular and less than a
single stride length, all of which strongly suggest that they
were registered by a group of six individuals moving
together as a coherent group, regardless of possible phys-
iographic control.Because the sedimentology indicates a
relatively rapid emplacement and subsequent burial of the
trackways, a scenario in which six similarly sized individ-
uals independently generated parallel, regularly spaced,
nonoverlapping trackways is highly unlikely.
Whether such an aggregation of similarly sized individ-
uals represents a common or rare (or perhaps seasonal)
event cannot be determined from a single find, but it
indicates that dromaeosaurids in fact engaged in some type
Fig. 4 Left foot of a seriema (Cariama cristata) in plantar view,
exhibiting a large heel pad (arrow) below the metatarsalphalangeal
joints. This specimen was defleshed and dried, so the heel pad would
have been larger in life
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of group behavior. Whether this behavior was specifically
hunting cannot be ascertained from the present track
sample, but Roach and Brinkman (2007) claimed that
cooperative hunting arises secondarily from group mainte-
nance and that extant animals that maintain social group-
ings typically do so for primary reasons other than hunting.
Thus, the fact that the Dromaeopodus track makers behaved
gregariously implies that cooperative hunting cannot be
ruled out. Primarily solitary hunting tactics for dromaeo-
saurs were proposed by Roach and Brinkman (2007) based
on phylogenetic bracketing of diapsid behaviors combined
with taphonomic interpretation and evidence of intraspe-
cific aggression in Deinonychus. Roach and Brinkman
(2007) proposed that trackway data previously presented in
support of gregarious nonavian theropods are perhaps better
interpreted as coincidental instances of normally solitary
individuals converging on a common point (e.g., food
source). While we agree that some footprint associations
may have been misinterpreted as gregarious, many con-
vincing examples remain (see Lockley and Matsukawa
(1999) for review). Group behavior more parsimoniously
explains their numbers and diversity through the Mesozoic
than does postulating that all such occurrences coinciden-
tally represent parallel trackway segments of otherwise
divergent trackways. Furthermore, the regularity and
narrow intertrackway spacing of the Dromaeopodus group
trackways are comparable to data that Roach and Brinkman
(2007, p. 127) agree are supportive of hypothesized gre-
garious behavior in herbivorous dinosaurs. Thus, the prob-
ably dromaeosaurid Dromaeopodus track makers were
apparently capable of nonagonistic group behaviors compa-
rable to those inferred for some herbivorous dinosaurs
(Lockley 1989), and not limited to random, agonistic en-
counters between individuals, as in Komodo dragons (contra
Roach and Brinkman 2007).
Paleobiogeography
Footprint size, varying between 26 and 28.5 cm in the
better preserved Dromaeopodus tracks, is consistent with a
track maker comparable to Achillobator (Perle et al. 1999)
in size (Table 1; see S2,S3, and S4 for formula and
measurements), providing the first evidence that such
animals were locally abundant in the Early Cretaceous of
East Asia. Whereas the sizeable Utahraptor (Kirkland et al.
1993) is known from roughly contemporaneous deposits of
North America (Kirkland 2005), large dromaeosaurid
fossils are unknown in Asia until the SantonianCampanian
Bayn Shire Formation of Mongolia that yielded Achilloba-
tor (Perle et al. 1999). Recent phylogenetic research
confirms that dromaeosaurids of this size are monophyletic
(Norell et al. 2006; Senter 2007; Senter et al. 2004; Turner
et al. 2007) and that the clade of BarremianMaastrichtian,
Laurasian dromaeosaurids originated in Asia. The inferred
BarremianAptian age of the track-bearing Tianjialou
Formation indicates that the taxonomic diversity, and at
least two orders of magnitude in body size disparity (Turner
et al., unpublished data) of Laurasian dromaeosaurs,
appeared almost simultaneously in the Asian and North
American fossil records, very soon after the earliest-known
occurrences of primitive members of this lineage in the
Yixian Formation of Liaoning (Norell and Xu 2005).
Coupled with current phylogenetic hypotheses in which
Asia appears to be the center of origin for Laurasian
dromaeosaurids (Norell et al. 2006; Senter 2007), the
footprint component of the diverse, Early Cretaceous,
Asian dromaeosaurid fauna lends some support to the pre-
diction that this continent served as a source of biogeo-
graphic dispersal of large (Utahraptor) and medium-sized
(Deinonychus) dromaeosaurids to North America during or
shortly before the Barremian. This could have occurred
across a Beringian land bridge (Plafker and Berg 1994), as
indicated by some other dinosaurs (Carpenter et al. 2002;
Kirkland et al. 1997,2005), albeit earlier than previously
hypothesized (Cifelli et al. 1997); alternatively, exchange
occurred across a Eurasian-eastern North American route
(Chinnery et al. 1998; Kirkland 2005). Determination of
which scenario is better supported awaits further discover-
ies; the tracks described in this study suggest that the trace
fossil record has the potential to contribute further
information in this regard.
Acknowledgments This study was supported financially in part
by National Natural Science Foundation of China grant 40572011 to R-
H. L. Additional support was provided by the University and Society
Collaboration of the Japanese Ministry of Education, grant-in-aid
1183303, 1999-2000 to M. M., and by the University of Colorado at
Denver Dinosaur Tracks Museum to M. G. L. M.A.N. and P.J.M. were
both supported by US National Science Foundation AToL EAR
0228607 and by the AMNH and FMNH, respectively. S. Harris
produced the movie and M. Ellison photographed the seriema foot for
Fig. 4.
References
Barsbold R (1998) Fighting dinosaursthey really fought. In: de
Carvalho AMG, Cachão MAP, Andrade AMPSAF, da Silva
CAPFM, dos Santos VAF (eds) I Encontro Internacional sobre
Paleobiologia dos Dinossáurios: Programa de Musealização para
Pistas de Dinossáurios em Portugal. Museu Nacional de História
Natural, Lisbon, pp 7478
Brinkman DL, Cifelli RL, Czaplewski NJ (1998) First occurrence of
Deinonychus antirrhopus (Dinosauria: Theropoda) from the
Antlers Formation (Lower Cretaceous: AptianAlbian) of Okla-
homa. Okla Geol Surv Bull 146:127
Carpenter K (1998) Evidence of predatory behavior by carnivorous
dinosaurs. Gaia 15:135144
Carpenter K, DiCroce T, Gilpin D, Kinneer B, Sanders F, Tidwell V,
Shaw A (2002) Origins of the Early and middleCretaceous
Naturwissenschaften
dinosaurs of North America: implications for plate tectonics.
Proceedings of the International Symposium on New Concepts in
Global Tectonics, May 2002, Otero Junior College, La Junta,
CO:289308
Chinnery BJ, Lipka TR, Kirkland JI, Parrish JM, Brett-Surman MK
(1998) Neoceratopsian teeth from the Lower to middle Creta-
ceous of North America. N M Mus Nat Hist Sci Bull 14:297302
Cifelli R, Kirkland JI, Weil A, Deino AL, Kowallis BJ (1997) High-
precision
40
Ar/
39
Ar geochronology and the advent of North
Americas Late Cretaceous terrestrial fauna. Proc Natl Acad Sci
94:1116311167
Currie PJ, Dong Z (2001) New information on Cretaceous troodontids
(Dinosauria, Theropoda) from the Peoples Republic of China.
Can J Earth Sci 38:17531766
Gaston R, Lockley MG, Lucas SG, Hunt AP (2003) Grallator-
dominated fossil footprint assemblages and associated enigmatic
footprints from the Chinle Group (Upper Triassic), Gateway area,
Colorado. Ichnos 10:153163
Gatesy SM, Middleton KM, Jenkins FA Jr, Shubin NH (1999) Three-
dimensional preservation of foot movements in Triassic theropod
dinosaurs. Nature 399:141144
Kirkland JI (2005) Utahs newly recognized dinosaur record from the
Early Cretaceous Cedar Mountain Formation. Utah Geol Surv
Notes 37:15
Kirkland JI, Gaston R, Burge D (1993) A large dromaeosaur
(Theropoda) from the Lower Cretaceous of eastern Utah.
Hunteria 2:116
Kirkland JI, Britt B, Burge DL, Carpenter K, Cifelli R, DeCourten F,
Eaton J, Hasiotis S, Lawton T (1997) Lower to middle Cretaceous
dinosaur faunas of the central Colorado Plateau: a key to under-
standing 35 million years of tectonics, sedimentology, evolution and
biogeography. Brigham Young Univ Geol Stud 42:69103
Kirkland JI, Zanno LE, Sampson SD, Clark JM, DeBlieux DD (2005)
A primitive therizinosauroid dinosaur from the Early Cretaceous
of Utah. Nature 435:8487
Li R, Lockley MG, Liu M (2005a) A new ichnotaxon of fossil bird
track from the Early Cretaceous Tianjialou Formation (Barre-
mianAlbian), Shandong Province, China. Chin Sci Bull
50:11491154
Li R-H, Liu M-W, Lockley MG (2005b) Early Cretaceous dinosaur
tracks from the Houzuoshan Dinosaur Park in Junan County,
Shandong Province, China. Geol Bull Chin 24:277280 (in
Chinese with English abstract)
Li D, Azuma Y, Fugita M, Lee Y-N, Arakawa Y (2006) A preliminary
report on two new vertebrate track sites including dinosaurs from
the Early Cretaceous Hekou Group, Gansu Province, China. J
Paleontol Soc Korea 22:2949
Lockley MG (1989) Tracks and traces: new perspectives on dinosaurian
behavior, ecology, and biogeography. In: Padian K, Chure DJ (eds)
The Age of Dinosaurs. Short courses in paleontology 2. The
Paleontological Society, Knoxville, pp 134145
Lockley MG, Matsukawa M (1999) Some observations on trackway
evidence for gregarious behavior among small bipedal dinosaurs.
Palaeogeogr Palaeoclimatol Palaeoecol 150:2531
Lockley MG, White D, Kirkland J, Santucci V (2004) Dinosaur tracks
from the Cedar Mountain Formation (Lower Cretaceous), Arches
National Park, Utah. Ichnos 11:285293
Lockley MG, Kim SH, Kim JY, Matsukawa M, Li R, Li J, Yang S-Y
(2007a) Minisauripusthe track of a diminutive dinosaur from
the Cretaceous of China and Korea: implications for stratigraphic
correlation and theropod foot morphodynamics. Cret Res,
in press
Lockley MG, Li R, Harris JD, Matsukawa M, Liu M (2007b) Earliest
zygodactyl bird feet: evidence from Early Cretaceous roadrunner-
like tracks. Naturwissenschaften 94:657665
Makovicky PJ, Norell MA (2004) Troodontidae. In: Weishampel DB,
Dodson P, Osmólska H (eds) The Dinosauria, 2nd Edition.
University of California Press, Berkeley, pp 184195
Makovicky PJ, Apesteguía S, Agnolin F (2005) The earliest dromaeo-
saurid theropod from South America. Nature 437:10071011
Maxwell WD, Ostrom JH (1995) Taphonomy and paleobiological
implications of Tenontosaurus-Deinonychus associations. J Vertebr
Paleontol 15:707712
Norell MA, Makovicky PJ (1997) Important features of the dromaeo-
saur skeleton: information from a new specimen. Am Mus Novit
3215:128
Norell MA, Xu X (2005) Feathered dinosaurs. Ann Rev Earth Planet
Sci 33:277299
Norell MA, Clark JM, Turner AH, Makovicky PJ, Barsbold R, Rowe T
(2006) A new dromaeosaurid theropod from Ukhaa Tolgod
(Ömnögov, Mongolia). Am Mus Novit 3545:151
Ostrom JH (1969) Osteology of Deinonychus antirrhopus, an unusual
theropod from the Lower Cretaceous of Montana. Bull Peabody
Mus Nat Hist 30:1165
Ostrom JH (1972) Were some dinosaurs gregarious? Palaeogeogr
Palaeoclimatol Palaeoecol 11:287301
Ostrom JH (1990) Dromaeosauridae. In: Weishampel DB, Dodson P,
Osmólska H (eds) The Dinosauria. University of California
Press, Berkeley, pp 269279
Perle A, Norell M, Clark J (1999) A new maniraptoran theropod
Achillobator giganticus (Dromaeosauridae)from the Upper
Cretaceous of Burckhant, Mongolia. Contrib Mong-Am Mus
Paleontol Proj 101:1105
Plafker G, Berg HC (1994) Overview of the geology and tectonic
evolution of Alaska. In: Plafker G, Berg HC (eds) The Geology
of Alaska. The Geology of North America G-1. Geological
Society of America, Boulder, pp 9891021
Roach BT, Brinkman DB (2007) A reevaluation of cooperative pack
hunting and gregariousness in Deinonychus antirrhopus and
other nonavian theropod dinosaurs. Bull Peabody Mus Nat Hist
48:103138
Russell DA, Dong Z (1993) The affinities of a new theropod from the
Alxa Desert, Inner Mongolia, Peoples Republic of China. Can J
Earth Sci 30:21072127
Senter P (2007) A new look at the phylogeny of Coelurosauria
(Dinosauria: Theropoda). J Syst Palaeontol doi:10.1017/
S1477201907002143
Senter P, Barsbold R, Britt BB, Burnham DA (2004) Systematics and
evolution of Dromaeosauridae (Dinosauria, Theropoda). Bull
Gunma Mus Nat Hist 8:120
Turner AH, Hwang SH, Norell MA (2007a) A small derived theropod
from Öösh, Early Cretaceous, Baykhangor Mongolia. Am Mus
Novit 3557:127
Turner AH, Pol D, Clarke JA, Erickson GM, Norell MA (2007b) A
basal dromaeosaurid and size evolution preceding avian flight.
Science 317:13781381
Xu X, Norell MA (2004) A new troodontid dinosaur from China with
avian-like sleeping posture. Nature 431:838841
Xu X, Norell MA, Wang X-L, Makovicky PJ, Wu X-C (2002) A basal
troodontid from the Early Cretaceous of China. Nature 415:780
784
Zhen S, Li J, Zhang B (1994) Dinosaur and bird footprints from the
Lower Cretaceous of Emei County, Sichuan, China. Mem Beijing
Nat Hist Mus 54:105120
Naturwissenschaften
... Deinonychosaur tracks are widely distributed in the Cretaceous of the Northern Hemisphere , especially in East Asia, where the greatest number of discoveries are known. Since the first report from the Emei tracksite of Sichuan Province (Zhen et al., 1994), deinonychosaur tracks have been found from more than ten localities in China (Xing et al., 2009(Xing et al., , 2013a(Xing et al., , 2013b(Xing et al., , 2015(Xing et al., , 2016a(Xing et al., , 2016b(Xing et al., , 2016c(Xing et al., , 2018a(Xing et al., , 2019a(Xing et al., , 2020Li et al., 2008;Wang et al., 2017), and several localities in South Korea (Kim et al., 2008(Kim et al., , 2012(Kim et al., , 2018. Many of these tracks are attributed to the following five ichnogenera: Velociraptorichnus (Zhen et al., 1994), Dromaeopodus , Dromaeosauripus (Kim et al., 2008), Menglongipus (Xing et al., 2009), and Dromaeosauriformipes (Kim et al., 2018). ...
... This ichnofamily is also diagnosed as "digit II represented by a short, round impression posteromedial to free part of digit III" . Probably, "free part" of Li et al. (2008) signifies the part of digit impression between toe and proximal phalangeal pad. Because all diagnostic features are represented in YWM 08381, we referred this specimen as the ichnofamily Dromaeopodidae. ...
... On the other hand, "free part" is not used in terminology of tetrapod ichnonology defined by Leonardi (1987). If our interpretation for "free part" of Li et al. (2008) is true, it is synonymous with the "digit length (or length of digit)", which is defined as "the measure of the line that unites the point of the nail (or claw or hoof) with the hind point of the last visible digital pad belonging to the digit under consideration" (Leonardi, 1987). Currently, five ichnogenera, including Velociraptorichnus from Sichuan Province (Zhen et al., 1994), Dromaeopodus from Shandong Province , Dromaeosauripus from South Korea (Kim et al., 2008), Menglongipus from Hebei Province (Xing et al., 2009), and Dromaeosauriformipes from South Korea (Kim et al., 2018), are known as deinonychosaur tracks. ...
Article
The new deinonychosaur trackway was recovered from the lower Upper Cretaceous Jinhua Formation of Zhejiang Province, southeastern China. This trackway includes nine well-preserved tracks characterized by elongate and didactyl morphology, and thus is assigned to the ichnospecies Velociraptorichnus sichuanensis. This trackway enables more accurate estimations of the speed and gait of the trackmaker for the ichnogenus Velociraptorichnus than the previous studies because the latter is based only on two consecutive tracks. Due to substantial differences in hindlimb proportions between the two clades assignable to the trackmaker of Velociraptorichnus, namely Dromaeosauridae and Troodontidae, we calculated the speed of trackmaker for each pattern. The estimated speeds resulted in 6.1 km/h for dromaeosaurids and 4.6 km/h for troodontids, both of which indicate that this trackway was made by a walking gait. This is the first record of a deinonychosaur trackway from the Cretaceous of southeastern China and extends the known distribution of didactyl theropod ichnotaxa. In combination with previous studies, it also suggests that a diverse ichnoassemblage of non-avian theropods was widely distributed in East Asia during that time.
... The Tyrants Aisle dinosaur tracksite close association between these two trackways, their similar pace lengths, and the observation that small tridactyl theropod-like tracks are rare elsewhere across the~1, 400 m 2 tracksite (n�4, not including these trackways), we conclude that the two trackmakers of Th.Tw4.71A-70-A and Th.Tw5.71-A-72-A were probably travelling together. These data are consistent with trackway (e.g., [17,[127][128][129][130][131]) and skeletal (e.g., [132][133][134][135][136]) evidence from elsewhere that indicates gregariousness-whether periodic or sustained-was present in a range of theropod clades and body sizes. ...
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The Wapiti Formation of northwest Alberta and northeast British Columbia, Canada, preserves an Upper Cretaceous terrestrial vertebrate fauna that is latitudinally situated between those documented further north in Alaska and those from southern Alberta and the contiguous U.S.A. Therefore, the Wapiti Formation is important for identifying broad patterns in vertebrate ecology, diversity, and distribution across Laramidia during the latest Cretaceous. Tracksites are especially useful as they provide a range of palaeoecological, palaeoenvironmental, and behavioural data that are complementary to the skeletal record. Here, we describe the Tyrants Aisle locality, the largest in-situ tracksite known from the Wapiti Formation. The site occurs in the lower part of Unit 4 of the formation (~72.5 Ma, upper Campanian), exposed along the southern bank of the Redwillow River. More than 100 tracks are documented across at least three distinct track-bearing layers, which were deposited on an alluvial floodplain. Hadrosaurid tracks are most abundant, and are referable to Hadrosauropodus based on track width exceeding track length, broad digits, and rounded or bilobed heel margins. We suggest the hadrosaurid trackmaker was Edmontosaurus regalis based on stratigraphic context. Tyrannosaurids, probable troodontids, possible ornithomimids, and possible azhdarchid pterosaurs represent minor but notable elements of the ichnofauna, as the latter is unknown from skeletal remains within the Wapiti Formation, and all others are poorly represented. Possible social behaviour is inferred for some of the hadrosaurid and small theropod-like trackmakers based on trackway alignment, suitable spacing and consistent preservation. On a broad taxonomic level (i.e., family or above), ichnofaunal compositions indicate that hadrosaurids were palaeoecologically dominant across Laramidia during the late Campanian within both high-and low-latitude deposits, although the role of depositional environment requires further testing.
... Of these clades, eudromaeosaurs are the best represented, with specimens known from Europe, Asia, and North America testifying to a diverse radiation of mostly small to midsized terrestrial predators (Turner et al., 2012;Pittman et al., 2020). Exceptional eudromaeosaur fossils provide potential evidence of pack hunting and demonstrate that these animals habitually predated upon prey larger than themselves (Maxwell and Ostrom, 1995;Barsbold and Osmólska, 1999;Li et al., 2008). ...
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Dromaeosaurid theropods represent a rare but important clade of nonavialan dinosaurs. Their close evolutionary relationship to modern birds has placed them at the center of paleonto-logical research for the last several decades. Herein we describe a new species of dromaeosaurid-Kuru kulla, gen. et sp. nov.-based on a partial skeleton from the Late Cretaceous Khulsan locality (Barun Goyot Formation) of Mongolia. This species is diagnosed by several autapomorphies within Dromaeosauridae, including a sharp groove anterior and ventral to the narial fossa on the premaxilla, a posterolaterally directed hornlet on the posterodorsal process of the lacrimal, a deep surangular bearing two surangular foramina, and anteriorly displaced pleurocoels on the dorsal centra. The taxon is further characterized by a unique combination of characters, including a mediolaterally narrow metatarsal II, serrations on both carinae of the dentary teeth, hyposphenes that are widely separated but joined by a web of bone, and a lacrimal with a poorly developed boss on its lateral surface. Phylogenetic analysis finds Kuru kulla to be the sister taxon of Adasau-rus mongoliensis, from the slightly later Nemegt Formation, with which it is united by three synapomorphies: a posterior surangular foramen that is ~30% the depth of the surangular, absence of a fourth trochanter of the femur, and thoracic centra that are markedly longer than their mid-point widths. The recognition of this taxon has important implications for common assumptions of Mesozoic terrestrial ecosystem structure and adds new data to a recently recognized pattern in dromaeosaurid faunal composition among Late Cretaceous localities in Mongolia and Inner Mon-golia (Nei Mongol Autonomous Region, China).
... This could conceivably be interpreted as the short digit II trace characteristic of deinonychosaurian tracks. However, although variably, even poorly preserved deinonychosaurian tracks are known from similar facies in the Cretaceous of China (Zhen et al. 1994;Li et al. 2007;Xing et al. 2009a), the sample size and quality of preservation in JYX-TI3 and JYX-T2 do not allow such tenuous speculation. ...
Article
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The Jiaguan Formation and the underlying Feitianshan Formation (Lower Cretaceous) in Sichuan Province yield multiple saurischian (theropod–sauropod) dominated ichnofaunas. To date, a moderate diversity of six theropod ichnogenera has been reported, but none of these have been identified at the ichnospecies level. Thus, many morphotypes have common “generic” labels such as Grallator , Eubrontes, cf. Eubrontes or even “ Eubrontes - Megalosauripus ” morphotype. These morphotypes are generally more typical of the Jurassic, whereas other more distinctive theropod tracks ( Minisauripus and Velociraptorichnus ) are restricted to the Cretaceous. The new ichnospecies Eubrontes nobitai ichnosp nov. is distinguished from Jurassic morphotypes based on a very well-preserved trackway and represents the first-named Eubrontes ichnospecies from the Cretaceous of Asia.
... and Di.I.34E to Velociraptorichnus based on greater relative shortness of digit IV compared with III and the absence of a digit II proximal pad impression. Dromaeopodus shandongensis was named by Li et al. (2008) on the basis of well-preserved trackways of Early Cretaceous age in Shandong Province, China. These tracks display a proximal pad impression of digit II, subequal digit III and IV lengths, and are larger than the Wapiti specimens (length, 24-28.5 cm; Li et al. 2008, table 1). ...
Article
Late Cretaceous tracks attributable to deinonychosaurs in North America are rare, with only one occurrence of Menglongipus from Alaska and two possible, but indeterminate, occurrences reported from Mexico. Here we describe the first probable deinonychosaur tracks from Canada: a possible trackway and one isolated track on a single horizon from the Upper Cretaceous Wapiti Formation (upper Campanian) near Grande Prairie in Alberta. The presence of a relatively short digit IV differentiates these from argued dromaeosaurid tracks, suggesting the trackmaker was more likely a troodontid. Other noted characteristics of the Wapiti specimens include a rounded heel margin, the absence of a digit II proximal pad impression, and a broad, elliptical digit III. Monodactyl tracks occur in association with the didactyl tracks, mirroring similar discoveries from the Early Cretaceous Epoch of China, providing additional support for their interpretation as deinonychosaurian traces. Although we refrain from assigning the new Wapiti specimens to any ichnotaxon because of their relatively poor undertrack preservation, this discovery is an important addition to the deinonychosaur track record; it helps to fill a poorly represented geographic and temporal window in their known distribution, and demonstrates the presence of a greater North American deinonychosaur ichnodiversity than has previously been recognized.
... Deinonychosaurian ichnotaxa comprise four ichnogenera that represent a considerable size range (Velociraptorichnus, Dromaeosauripus, Menglonipus and Dromaeopodus). Our tracks and trackways closely resemble the ichnotaxon Dromaeopodus shangdongensis known from the Tianjialou Formation (Barremian-Aptian) from the Shandong Province in China (Li et al., 2008). The footprint length of the Bolivian tracks is almost twice that of their Asian counterparts. ...
Article
We present an update and a review of the Late Cretaceous dinosaur tracksites of Bolivia. The Puca Group (Coniacian – Late Maastrichtian) records the tracks and trackways of two different titanosaurid sauropods, ankylosaurs, hadrosaurs and different theropod groups from the Central Andean lacustrine back arc basin. We review the sites from the Maragua syncline (Chuquisaca) and present new data on the famous Toro Toro site (Potosi). Furthermore, the first complete map of the world’s largest dinosaur tracksite, Cal Orck’o (El Molino Formation, Sucre) gives an insight into behavior and movement patterns. Parallel trackways of subadult ankylosaurs provide the first unequivocal evidence of social behavior amongst these dinosaurs worldwide. The El Molino Formation and the coeval deposits of Southern Peru and Northern Argentina form a megatracksite with a size of around 100,000 km2. The paleogeographic position of the main sites within the basin suggests that they are part of a seasonal migration route along the shoreline and deltas of an ancient lake system.
... By using the formula of Alexander (1976), our estimation shows that the BTP-T9 trackmaker was walking (hip height = 4.5 × foot length for small theropods, and relative stride length 1.04 ≤ 2.0) (Thulborn, 1990) with a speed of ~0.65 m/s or ~2.34 km/h. To date, the best evidence of gregariousness among deinonychosaurs comes from a set of six parallel trackways of large deinonychosaurs from the Lower Cretaceous Tianjialou Formation of Shandong Province (Li et al., 2008). The limited evidence from the Baituping site suggests two individuals progressing along parallel trends. ...
Article
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Poorly preserved tracks have limited ichnotaxonomic or biotaxon utility, but may reveal useful information about the paleoenvironment, behavior and track taphonomy. Eight mostly parallel to sub parallel trackway segments (T1–T8) were registered on a truncation surface in the Lower Cretaceous Luohe Formation of Shaanxi Province. These attest to the passage of several bipeds, probably all theropods, in a paleo-contour-parallel, south-north direction in an arid setting. Quality of preservation in these trackways is poor, but notably superior in two additional trackways (T9–T10) on a foreset surface. Trackway T9 indicates a didactyl trackmaker, probably a deinonychosaurian, heading north to south. This is the 13th report of deinonychosaurian tracks from the Lower Cretaceous of China. If any or all the eight south-north oriented trackway segments represent continuations of other segments in the same trackways, the total number of individual trackmakers heading in this direction may have been as low as three. Although the trackway pattern and sedimentological evidence could indicate a physically controlled pathway influencing the direction taken by these trackmakers, the possibility that the trackways also represented small social or gregarious group cannot be ruled out.
... Luanchuanraptor, known from a partial skeleton, was discovered from the Campanian-Maastrichtian Qiupa Formation of Henan, central China (Lü et al., 2007), and a recent analysis found it closely related to its Late Cretaceous Mongolian relative Velociraptor (Pei et al., in press). Tracks of two differently sized coeval deinonychosaurs have been found in the Barremian-Aptian Tianjialoue Formation of Shandong, eastern China, but the identity of their makers remains elusive (Li et al., 2008a). ...
Chapter
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An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaurians are bizarre, nonparavian pennaraptorans first discovered in North America and Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia. Early Cretaceous material from China preserves feathers and other soft tissues and ingested remains including gastroliths and other stomach contents, while brooding specimens and age-structured, single-species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and possibly other scansoriopterygids may represent early-diverging oviraptorosaurians. Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverging oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans. Known from five (or possibly six) feathered specimens from China, only two mature individuals exist, representing these taxa. These taxa, Yi and Ambopteryx, preserve stylopod-supported wing membranes that are the only known alternative to the feathered, muscular wings that had been exclusively associated with dinosaurian flight. Thus, scansoriopterygid specimens-particularly those preserving soft tissue-remain a key priority for future specimen collection. Dromaeosaurids and troodontids were first discovered in North America and Mongolia in Late Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic, were strikingly feathered, lived across diverse climes and environments, and at least in the case of dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
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Since the 1969 description of Deinonychus antirrhopus Ostrom, cooperative pack hunting behavior for this species and, subsequently, for many other nonavian theropods, has attained wide acceptance. In this paper we assess the hypothesis of mammal-like cooperative pack hunting in D. antirrhopus and other nonavian theropods by examining the behaviors of extant diapsids. Through phylogenetic inference and character optimization, we conclude that this hypothesis is both unparsimonious and unlikely for these taxa and that the null hypothesis should therefore be that nonavian theropod dinosaurs were solitary hunters or, at most, foraged in loose associations. Moreover, we present new evidence from the D. antirrhopus type locality of probable intraspecific aggression in this species. Additionally, our study suggests that some evidence that has previously been proposed in support of highly gregarious, mammal-like behavior in nonavian theropods (e.g., certain theropod-dominated fossil assemblages, preserved bite-mark injuries on some specimens, and the preponderance of theropod trackways at some sites) may alternatively be interpreted as evidence that nonavian theropod behavior was more agonistic, cannibalistic, and diapsid-like than has been widely believed.
Conference Paper
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The Cedar Mountain and Dakota Formations of eastern Utah preserve two distinct biostratigraphical dinosaur faunas that record the severing of a North American-European connection, and the opening of an North American-Asian connection as the North American Plate drifted westward. The older Yell ow Cat Fauna, of the Yellow Cat through to the lower Ruby Ranch Members of the Cedar Mountain Formation, is dominated by polacanthid ankylosaurs, brachiosaurid and titanosaurid sauropods, and iguanodontids much like those of the Wealden of southern England. The polacanthid ankylosaur, the brachiosaurid sauropods and a coelurosaurid theropod indicates that the Yellow Cat Fauna is a relict of the older Late Jurassic Morrison Fauna. The younger Mussentuchit Fauna from the top of the Ruby Ranch and Mussentuchit Members and from the Dakota Formation, shows an Asian influence as characterized by a shamosaur-like ankylosaurid similar to those of Asia, the first appearance of a neoceratopsian, and the presence of the triconodont mammal, Gobiconodon. Various age dates on the faunas indicate that separation between the North America and western part of the Eurasian Plates was completed by the end of the Barremian and that a connection between North American and eastern Eurasian Plates was established no later than the early Albian.
Article
Troodontid specimens were recovered from three localities in China by the Sino-Canadian expeditions between 1987 and 1990. These include a Lower Cretaceous form (Sinornithoides youngi), which is the most complete troodontid skeleton ever found, isolated bones from the Iren Dabasu Formation (? Turonian), and partial skeletons of Saurornithoides mongoliensis from Djadokhta-equivalent beds (? Campanian). These, and other specimens recently described from North America, allow a better assessment of the phylogenetic position of troodontids than has been possible before. Although troodontids have autapomorphies that eliminate them from consideration as bird ancestors, they are nevertheless one of the closest avian outgroups within the Theropoda.
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.