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First Report of Small Ornithopodichnus Trackways from the Lower Cretaceous of Sichuan, China

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Trackways of ornithopods are well-known from the Lower Cretaceous of East Asia, particularly in Korea and China. However, most morphotypes have been identified as Caririchnium which is characterized by moderate mesaxony, the ratio length = width, or length > width and, in some cases, by a quadrupedal gait. In 2009 the ichnogenus Ornithopodichnus, which exhibits distinctively weak mesaxony and a broader, transverse pes imprint with the ratio length Ornithopodichnus in China, the trackmaker being a moderately large quadruped. In 2012, Ornithopodichnus was described on the basis of well-preserved material from the Upper Cretaceous of Korea, in this case left by a small, gregarious biped. Herein we document, a fourth occurrence of Ornithopodichnus in the Lower Cretaceous Feitianshan Formation of Sichuan, China which is a further example of trackways that can be attributed to small, bipedal and gregarious ornithopods. Morphology, size, trackway pattern and speed of locomotion correspond well with trackways known from the Korean Hwasun tracksite. Possibly, the occurrence of Ornithopodichnus which is restricted to East Asia thus far, is related to ecological and biogeographical pecularities in this area.
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First Report of Small Ornithopodichnus Trackways from the
Lower Cretaceous of Sichuan, China
Lida Xing
1
and Martin G. Lockley
2
1
School of the Earth Sciences and Resources, China University of Geosciences, Beijing, China
2
Dinosaur Trackers Research Group, University of Colorado, Denver, Colorado, USA
Trackways of ornithopods are well-known from the Lower
Cretaceous of East Asia, particularly in Korea and China.
However, most morphotypes have been identified as Caririchnium
which is characterized by moderate mesaxony, the ratio length D
width, or length >width and, in some cases, by a quadrupedal
gait. In 2009 the ichnogenus Ornithopodichnus, which exhibits
distinctively weak mesaxony and a broader, transverse pes
imprint with the ratio length <width, was identified in Korea, on
the basis of material with suboptimal preservation. The
trackmaker was a large ornithopod. Subsequently, in 2009 a
second report recognized Ornithopodichnus in China, the
trackmaker being a moderately large quadruped. In 2012,
Ornithopodichnus was described on the basis of well-preserved
material from the Upper Cretaceous of Korea, in this case left by
a small, gregarious biped. Herein we document, a fourth
occurrence of Ornithopodichnus in the Lower Cretaceous
Feitianshan Formation of Sichuan, China which is a further
example of trackways that can be attributed to small, bipedal and
gregarious ornithopods. Morphology, size, trackway pattern and
speed of locomotion correspond well with trackways known from
the Korean Hwasun tracksite. Possibly, the occurrence of
Ornithopodichnus which is restricted to East Asia thus far, is
related to ecological and biogeographical pecularities in this area.
Keywords Ornithopod tracks, Ornithopodichnus, Lower Creta-
ceous, China
INTRODUCTION
Tracking Ornithopods
Numerous reports of ornithopod trackways are known from
East Asia, especially from Korea and China, including those
that represent both bipeds and quadrupeds, and many sites that
indicate gregarious behavior. Nevertheless, relatively few
Asian examples have been determined at the ichnospecies
level and in many cases, ornithopod tracks have been given
generalized ichnotaxonomic labels. For example most
ornithopod trackways from the footprint-rich Jindong Forma-
tion of Korea have been assigned to the ichnogenus Carir-
ichium (Lockley et al., 2006), with no ichnospecies
designation. The same ichnogenus label has been applied to
trackways from the Uhangri Formation (Huh et al., 2003). In
both of these, ichnofaunas the trackmakers appear to have
been bipeds. Caririchium is also recognized in the Lower Cre-
taceous of China (Xing et al., 2007) where it is represented by
the ichnospecies C. lotus indicative of a quadrupedal track-
maker and being morphologically similar to C. leonardii from
the Cretaceous of Colorado (Lockley, 1987; Lockley et al.,
2001). However, as noted below, some Cretaceous ornithopod
tracks appear to be readily distinguishable from Caririchium
on morphological grounds (Lockley et al., in press). These
include the ichnogenus Ornithopodichnus, hitherto reported
from two localities in Korea and one in China, as well as from
the newly reported locality described here.
Ornithopodichnus
The ichnogenus Ornithopodichnus (type ichnospecies Orni-
thopodichnus masanensis) currently remains as a monoichno-
specific ichnogenus. It was originally described by Kim et al.
(2009) as a distinctive, robust ornithopod track, which is wider
than long (mean length/width [l/w] ratio 0.90; range 0.64–
1.18), with positive (inward) rotation, and very thick, broad
and U-shaped toe impressions creating a trefoil outline with a
smoothly rounded hind margin. Lockley (2009) pointed out
that Ornithopodichnus has a very short middle toe (digit III
trace) relative to digits II and IV, thus exhibiting “weak
mesaxony” in comparison with other ornithopod ichnotaxa.
Although no attempt was made to identify the trackmaker of
the Korean footprints at a low ichnotaxonomic level, Kim
et al. (2009) pointed out that some Cretaceous ornithopods,
including the Asian genus Zhouchengosaurus, also exhibit
weak mesaxony.
Additional examples of Ornithopodichnus with the distinc-
tive low l/w ratio (0.84–0.86) were described from well-pre-
served trackways as the Hwasun site in Korea (Huh et al.,
Address correspondence to Lida Xing, School of the Earth Scien-
ces and Resources, China University of Geosciences, Beijing 100083,
China. E-mail: xinglida@gmail.com
213
Ichnos, 21:213–222, 2014
Copyright ÓTaylor & Francis Group, LLC
ISSN: 1042-0940 print / 1563-5236 online
DOI: 10.1080/10420940.2014.951998
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FIG. 1. Geographic map indicating the location of the Zhaojue dinosaur footprint tracksites I and II in Liangshan Yi Autonomous Prefecture, Zhaojue County,
Sichuan Province, China.
FIG. 2. Zhaojue dinosaur tracksite II. A. Overview of section with steep track surface. B. Track surface with Ornithopodichnus trackways.
214 L. XING AND M. G. LOCKLEY
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2006; Lockley et al., 2012a) where they represent small
bipedal trackmakers, evidently moving in the same direction
as a small group of six individuals. A single large Ornithopo-
dichnus track was also recorded at the Hwasun locality having
the size of the smallest of the larger tracks from the O. masa-
nensis type locality. A similar, large, transverse ornithopod
track morphotype, first reported from the Lower Cretaceous,
Houzuoshan Dinosaur Park site in Shandong Province by Mat-
sukawa and Lockley (2007), was subsequently given the label
Ornithopodichnus by Lockley (2009). Two trackways were
illustrated, one indicating a bipedal trackmaker, the other a
quadruped. In summary, including the present report,
FIG. 3. Stratigraphic sections at Zhaojue dinosaur tracksites I and II.
ORNITHOPODICHNUS TRACKWAYS, LOWER CRETACEOUS, CHINA 215
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Ornithopodichnus is known from two localities in Korea and
two in China:
Ornithopodichnus masanensis, Jindong Formation (Creta-
ceous), Masan site, Korea, representing at least six large
bipeds (Kim et al., 2009).
Ornithopodichnus, (ichnosp. indet.), Tianjialou Formation
(Cretaceous), Houzuoshan Dinosaur Park site, near Junan,
Shandong Province, China, representing a large biped and a
large quadruped (Matsukawa and Lockley, 2007; Lockley,
2009).
Ornithopodichnus (ichnosp. indet.), unnamed formation
(Cretaceous), Hwasun site Korea, representing six small
bipeds and one large biped (Lockley et al., 2012a).
Ornithopodichnus (ichnosp. indet.), Feitianshan Formation,
China (this study) representing three small bipeds (this
article).
The Ornithopodichus morphotype is distinguished from
ornithopod tracks such as Caririchnium (Leonardi, 1984;
Lockley, 1987; Lockley and Wright, 2001; Xing et al., 2007)
by very weak mesaxony (Lockley, 2008, 2009) which
obviously seems to be correlated with variation in the mesax-
ony that has been observed in the pes skeletons of large orni-
thopods. For example, Kim et al. (2009) show unequivocally
that there is variation in the relative length of the toes of
Iguanodon species. Thus, Iguanodon atherfieldensis can be
described as showing much stronger mesaxony (a more promi-
nent digit III) than Iguanodon bernissartensis, and that the feet
of large ornithopods like Zhuchengosaurus (DShantungosau-
rus; Ji et al., 2011) show extremely weak mesaxony (Zhao
et al., 2007). The differences between I. bernissartensis and I.
atherfieldenis were considered by Paul (2007) of sufficient
importance to transfer the latter species to the new genus Man-
tellisaurus (i.e., M. atherfieldensis). Among the differences
between the two former Iguanodon species noted by Paul
(2007) were the lengths of the fore limbs. Thus, given that
Lockley (2007, 2009) has drawn attention to recognizable
morphodynamic relationships between limbs and between
limb and foot proportions, the inferences of Kim et al. (2009)
that discernable morphological differences in the pes might be
recognizable in the footprints is plausible.
Thus, tracks such as Caririchnium likely represent track
makers similar to Iguanodon atherfieldensis with well-defined
FIG. 4. View of track-bearing section at the Zhaojue dinosaur tracks quarry (site ZJ-II). Note the main track bed is exposed at the top of a massive sandstone
overlain by an alternating sequence of muddy red siltstones 5–65 cm thick and sandstones 10–130 cm thick. The uppermost sandstone unit is a rich source of
copper.
216 L. XING AND M. G. LOCKLEY
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or stronger mesaxony, whereas Ornithopodichnus appears to
represent a trackmaker like Zhuchengosaurus with much
weaker mesaxony. This variation in mesaxony is obviously
independent from track size and ontogenetic growth because
(weak mesaxonic) Ornithopodichnus comprises footprints of
large and small individuals. In naming Ornithopodichnus Kim
et al. (2009) noted that Moratalla (1993) had informally pro-
posed the name ‘Brachyguanodonipus prejanensis’ for large
ornithopod tracks that are unusually wide (mean length and
width values of 53.0 and 64.3 cm respectively) giving a l/w
ratio of 0.82 (Lockley, 2009). However, as the name was pro-
posed in an unpublished PhD thesis (in Spanish) it has no for-
mal status in ichnotaxonomy.
In the present study we describe small Ornithopodichnus
trackways from the northern part of tracksite II (prefix ZJ-
IIN), which we infer to be very similar to those reported from
the Lower Cretaceous of Korea (Lockley et al., 2012a).
GEOLOGICAL SETTING
The Zhaojue site is a large active copper mine quarry in the
Lower Cretaceous Feitianshan Formation (Berriasian–Barre-
mian; Tamai et al., 2004) of Sichuan Province (Figs. 1–3).
The outcrops in this area are dominated by thick sandstone
sequences with minor siltstones and shale, which alternate
with thick brick red shale and siltstone sequences, which in
turn contain thin sandstones (Fig. 4). The quarry sequence
reveals tracks at several levels including impressions (concave
epireliefs) on the surfaces of sandstone beds and natural casts
(convex hyporeliefs) on the underside of beds where sand has
filled in tracks made in shale or silt beds. The exposed sand-
stone surfaces are extensive and reveal many tracks, ripple
marks, desiccation cracks and other biogenic and non-biogenic
sedimentary features. The preservation of tracks is variable but
generally good to moderately good.
Tracks found on the most track-rich surfaces include large
theropod, sauropod and ornithopod tracks as well as pterosaur
footprints. A preliminary report on swim tracks attributable to
theropods, has recently be published (Xing et al., 2013), and
the pterosaur track occurrence has also been noted elsewhere
(He et al., 2013). Xing et al. (2013) referred to two main out-
crops, about 450 meters apart, designated as tracksites I and II.
Trackways from these sites have the prefixes ZJ-I and ZJ-II,
respectively. However, as noted by Xing et al. (2013), the
quarry configuration is changing constantly due to active exca-
vation. In the previous, preliminary study attention was
FIG. 5. Map of a part of Zhaojue site ZJ-IIN, showing three parallel Ornithopodichnus trackways (O1–O3). Compare with Figure 6.
ORNITHOPODICHNUS TRACKWAYS, LOWER CRETACEOUS, CHINA 217
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focused on swim tracks from tracksite II. Studies are ongoing
at both tracksite I and tracksite II, where multiple track-bear-
ing layers have been identified.
MATERIAL AND METHODS
Due to the steepness of the bedding planes (40–50) at both
tracksite I and tracksite II (Xing et al., 2013), it was necessary
to use ropes during the study of track-bearing surfaces. In
order to make accurate maps, especially in areas destined for
destruction by quarry operations, tracks were photographed,
outlined in chalk, and traced on large sheets of plastic. In addi-
tion a representative area of well-preserved tracks was mapped
by hand using a chalk grid (Fig. 5). Several natural casts were
collected, and latex molds of representative tracks were made.
Additional more detailed tracings of selected tracks were
made on transparent acetate film. Due to the difficulty of
obtaining accurate trackway measurements from steep slopes,
measurements for the present study were taken primarily from
the tracings and latex molds of representative tracks from three
trackways. Latex molds and plaster replicas are reposited in
the Huaxia Dinosaur Tracks Research and Development Cen-
ter collections (prefix HDT) and in the University of Colorado
Museum of Natural History collections, Boulder (USA) (prefix
UCM). Tracings are also reposited at both institutions.
Maps of three areas (part of tracksite I and parts of both the
northern and southern sectors of tracksite II) have been pre-
pared and will be published elsewhere. A map of the area with
the best preserved Ornithopodichnus tracks that shows a part
of the northern sector of tracksite II was also made as a base
map to help reference the tracings and latex molds collected in
that sector (Figs. 5 and 6). As shown in Figure 5, three parallel
Ornithopodichnus trackways have been designated as O1, O2
and O3. At least 21, 8, and 7 footprints are preserved,
individually.
Trackway O1 is the longest and most accessible trackway,
with the best preserved segments including the tracks desig-
nated as O1.1 through O1.6 (Tracing T1611 in the UCM
archive). Track O1.6 is the best preserved (Fig. 7). Track O1.1
in this sequence was replicated and is preserved in the UCM
collections as 214.265. Two sequential tracks in trackway O2
(i.e. tracks O2.7 and O2.8) were replicated as UCM 214.266,
and track O.3.3 from trackway O3 was molded and replicated
as UCM 214.267 (see Table 1, and UCM tracing T1613).
DESCRIPTION
As indicated in Table 1, trackway O1 represents a small
trackmaker (mean footprint length and width 12.97 and
15.30 cm, respectively), with wide feet (mean 1/w 0.83).
Trackway O2, is similar in size and also displays wide tracks
(l/w 0.91). Only one reliable measurement was obtained from
trackway O3, indicating tracks similar in size to O2 and O3
and about as wide as long (l/w 1.00). Digital pads are absent;
all the distal part of digits are deep, the claw marks are round
and blunt. Based on trackway O1, there is consistent inward
rotation ranging from 0–26
(mean »7
). Step averages »
40.0 cm (or 2.6 £footprint length) but appears to show a
deceleration from 47.2 to 32.0 cm in the segment measured in
detail. All three trackways are oriented toward the northwest.
COMPARISONS WITH OTHER ORNITHOPODICHNUS
TRACKS
As noted above Ornithopodichnus from Zhaojue is similar
in size and shape (l/w ratio 0.83–1.00: mean 0.91) to Ornitho-
podichnus tracks from the sample described by Lockley et al.
(2012a) from the Hwasun site in Korea (mean l/w ratio D
FIG. 6. Sketches with details of Ornithopodichnus trackways ZJ-IIN-O1–O3.
Compare with Figure 5.
218 L. XING AND M. G. LOCKLEY
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0.90; Table 2). It is also similar to the sample of much larger
Ornithopodichnus masanensis tracks described from the Jin-
dong Formation, Korea (Kim et al., 2009) that show a mean
l/w ratio of 0.90 (Table 2). Both samples contain long track-
ways, which make it possible to verify that the characteristic
features of the tracks, notably their transverse shape and ten-
dency to inward rotation, recur repeatedly in long trackways
and therefore seem to reflect anatomical peculiarities rather
than extramorphology and substrate condition. As noted by
Lockley et al. (2012a) the six small Ornithopodichnus track-
ways from Hwasun are particularly well-preserved, and have
yielded internally consistent measurements within the sample.
The three Zhaojue trackways (Fig. 5, Table 1) are more vari-
able in preservation, and it is difficult to obtain multiple
measurements from trackways O2 and O3 due to the diffi-
culty of access on a steep slope and the quality of preserva-
tion affected by weathering and trampling by other
trackmakers. Nevertheless, the following comparisons support
assigning the Zhaojue trackways (O1–3) to Ornithopodichnus
inferring that they are similar to the Hwasun trackways (O1–
O6). First the size and shape (l/w ratio) is similar in the two
samples. Thus, the mean length and width values for tracks
from the Zhaojue sample are 14.79 and 15.76 cm compared
with 11.98 and 13.34 for the Hwasun sample. Thus, on aver-
age, the Chinese tracks are 25% longer and 18% wider than
the Korean tracks. However, the best preserved Zhaojue
trackway (O1) is only slightly larger than the Korean tracks,
and we consider this trackway to produce the most reliable
data. Likewise the mean step for Zhaojue trackway O1, is
40.04 cm, which is very similar to the mean step of 38.49 cm
calculated for the entire Hwasun sample (Table 2). Other
notable points of comparison include the similarity in average
inward rotation (7.2
for Zhaojue trackway O1 and 10.5
for
the Hwasun sample).
Xing et al. (2013) also described several middle-sized, but
variably-shaped ornithopod tracks from ZJ-II. The length of
these tracks ranges between 18.2 and 28.7 cm, and the L/W
ratios are 0.78–1.48. But most of these tracks are poorly pre-
served and the fills are amalgamated to the tracks, making it
difficult to separate them mechanically. These tracks resemble
both Caririchnium and Ornithopodichnus in morphology.
Thus larger Ornithopodichnus from ZJ-IIN may be present.
SPEED ESTIMATES
As reported by Kim et al. (2009), all Ornithopodichnus
masanensis trackways are parallel and oriented in the same
(southward) direction. They also show consistent intertrack-
FIG. 7. Photograph and sketch of best preserved Ornithopodichnus track ZJ-IIN-O1.6.
TABLE 1
Measurements for small Ornithopodichnus tracks from the
Zhaojue site II
Track
number
Left/
right length : width l/w ratio Rotation Step
ZJ-IIN-O1.1 R 11.00 : 15.30 0.72 14
ZJ-IIN-O1.2 L 13.50 : 15.30 0.88 1647.20
ZJ-IIN-O1.3 R 12.50 : 15.80 0.79 041.50
ZJ-IIN-O1.4 L 13.00 : 14.80 0.88 035.50
ZJ-IIN-O1.5 R 14.30 : 14.40 0.99 934.00
ZJ-IIN-O1.6 L 13.50 : 16.20 0.83 432.00
O1 mean 12.97 : 15.30 0.85 7.238.04
ZJ-IIN-O2.7 13.90 : 15.50 0.90
ZJ-IIN-O2.8 16.10: 17.50 0.92
O2 mean 15.00 : 16.50 0.91 36.00
ZJ-IIN-O3.3 16.40 : 16.40 1.00
ORNITHOPODICHNUS TRACKWAYS, LOWER CRETACEOUS, CHINA 219
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way spacing (sensu Lockley, 1989). Such parallel ornithopod
trackways are quite common at Cretaceous sites in Asia (Lock-
ley et al., 2006; Zhang et al., 2006) and in North America
(Lockley and Hunt, 1995; Matsukawa et al., 1999) and are
usually considered indicative of gregarious behavior. Kim
et al. (2009) estimated the size and speed of the O. masanensis
trackmaker, using relative stride length (stride length/height at
the hip, or SL/h), and the equation, V (1.42h)
0.5
proposed
by Thulborn (1990) and references therein. The speed of the
Masan Ornithopodichnus trackmakers was estimated at 1.71
to 1.89 m/s, a relatively slow rate of progression. For consis-
tency, where reliable stride data are available, we estimated
the speeds of the Zhaojue and Hwasun trackmakers using the
same formula (Table 3). Zhaojue trackways O1 and O2 indi-
cate estimated speeds between 0.92 and 0.99 m/s, which com-
pare closely with the speeds estimated from small ornithopod
trackways from Hwasun (HO1–2 and HO4–5) which range
from 0.89–0.91 m/s. The large ornithopod trackway (LOT)
from Hwasun gives a speed estimate of 1.69 m/s, which is
very similar to the estimates derived from the large trackways
in the Masan sample.
DISCUSSION AND CONCLUSIONS
Small short (l<w) ornithopod tracks from the Zhaojue
locality represent the fourth report of the ichnogenus
TABLE 2
Mean measurements for small Ornithopodichnus trackways from the Cretaceous Zhaojue (China) and Hwasun and Masan track-
sites (Korea). O1- O6 and LOT (Large ornithopod trackway) from the Hwasun tracksite, modified after Lockley et al. (2012).
TW1–TW5 after Kim et al. (2009).
Trackway no. Pes length : width l/w Step : stride Rot. : pace angle
ZJ-IIN-O1 12.97 : 15.30 0.83 38.04 : 76.08* 7.20 : —
ZJ-IIN-O2 15.00 : 16.50 0.91 36.00 : 72.00*
ZJ-IIN-O3 16.40 : 16.40 1.00
O1-O3 mean 14.79: 15.76 0.91 38.02 : 76.04
O1 Hwasun 12.67 : 14.72 0.86 38.43 : 73.80 5.00 : 161.20
O2 Hwasun 12.07 : 14.03 0.86 40. 53 : 81.95 11.75 : —
O3 Hwasun (11.65) : 12.80 (0.91) 38.30 : —
O4 Hwasun (12.00) : 12.80 0.94 36.40 : 73.00
O5 Hwasun 12.13 : 14.50 0.84 38.30 : 75.75 14.80 : 156.00
O6 Hwasun 11.40 : 11.20 1.01
O1-O6 mean 11.98 : 13.34 0.90 38.39 : 76.12 10.52 : 158.60
LOT 35.10 : 41.70 0.84 114.25 : 225.00 13.80 : 154.30
TW1 35.85 : 56.00 0.64 80.33 : 156.80 — : 153.40
TW2 42.75: 47.75 0.89 95.40 : 189.33 — : 169.83
TW3 43.20 : 36.40 1.18 91.50 : 181.60 — : 165.00
TW4 36.33 : 39.66 0.92 80.60 : 159.75 — : 171.25
TW4’ 35.75 : 35.50 1.00 70.00 : 160.50
TW5 42.20 : 56.40 0.75 91.00 : 177.67 — : 161.00
TW1-5 mean 39.35 :45.29 0.90 84.81 : 170.94
*Indicates stride calculated as 2 £ step. Mean values in parentheses ( ) indicate that approximate measurements from original data have been included in
calculations.
TABLE 3
Estimated data of height at the hip and speed of Ornithopo-
dichnus producers. Trackways TWI-TW5 refer to the Masan
sample (after Kim et al., 2009). Trackways ZJ-IIN-O1–ZO2
refer to the Zhaojue sample and trackways HO1-2, HO4-5 and
LOT refer to the Hwasun sample
Trackway no. L (cm) SL (cm) h* (cm) SL/h V
#
(m/s)
TW1 38.0 155.0 217.0 0.72 1.76
TW2 44.0 190.0 251.0 0.76 1.89
TW3 44.0 182.0 251.0 0.73 1.89
TW4 37.0 160.0 211.0 0.76 1.73
TW4´36.0 160.0 205.0 0.78 1.71
TW5 42.0 177.0 239.0 0.69 1.84
ZJ-IIN-O1 13.0 80.8 59.8 1.35 0.92
ZJ-IIN-O2 15.0 72.0 69.0 1.04 0.99
HO1 12.7 73.8 58.4 1.26 0.91
HO2 12.1 82.0 55.7 1.47 0.89
HO4 12.0 73.0 55.2 1.32 0.89
HO5 12.1 75.8 55.7 1.36 0.89
LOT 35.1 225.0 200.0 1.12 1.69
L: track length, SL: stride length, SL/h: relative stride length (Thulborn, 1990).
*h D5.7L (height at the hip of large bipedal dinosaurs in general) and D4.6L
(small bipedal dinosaurs in general) after Thulborn, 1990.
#
VD(1.42h)
0.5
(average walking speed of bipedal dinosaurs after Thulborn,
1990).
220 L. XING AND M. G. LOCKLEY
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Ornithopodichnus from Asia since it was defined by Kim et al.
(2009). Two of these assemblages, one from Masan, Korea,
and the other from Junan, China represent large trackmakers.
In the Junan sample, one trackway indicates bipedal progres-
sion, the other one a quadrupedal movement. The other two
samples, from Hwasun, Korea and Zhaojue, China, both repre-
sent small trackmakers (footprint length »13.0–15.0 cm) that
created parallel trackways suggestive of gregarious behavior.
Based on footprint length, the hip heights of the dinosaurs
from both of these samples is in the range of 55–69 cm. The
regularity in step length and speed estimates from both sites
indicates that the trackmakers were moving slowly at about 1
meter/second. The Junan sample is the only one to have
yielded unequivocal evidence of quadrupedal progression by
an Ornithopodichnus trackmaker. Thus, although it is not pos-
sible to rule out overprinting of the manus by the pes (Paul,
1991), it appears that the majority of samples reflects bipedal
progression.
Ornithopod tracks occur abundantly in the Cretaceous. Lucas
(2007) therefore used them as indicators of a Lower Cretaceous
footprint-based biochron (Lucas, 2007). Six ornithopod ichnoge-
nera, Amblydactylus, Caririchnium, Iguanodontipus,Hadro-
sauropodus, Jiayinosauropus and Ornithopodichnus have been
erected on the basis of Cretaceous ichnites. This list does not
include tracks such as Iguanodonichnus that have been proven to
represent sauropods and Hadrosaurichnus, which represents a
theropod (Sarjeant et al., 1998). Three of these (Caririchnium,
Jiayinosauropus, and Ornithopodichnus) have been identified in
Asia (Lockley et al., 2013), with the latter two being based on
Asian holotypes (Dong et al., 2003, and Kim et al., 2009, respec-
tively). To date Ornithopodichnus has only been recognized in
Asia. Both Hadrosauropodus and Jiayinosauropus are Late Cre-
taceous ichnogenera of presumed hadrosaurid affinity. The other
ichnotaxa are reported fromthe Lower to mid Cretaceous.
Lucas et al. (2011, p. 357) recently suggested only two Cre-
taceous ichnogenera may be valid: “Caririchnium (DHadro-
sauropodus) and Amblydactylus (DIguanodontipus).”
However, this conclusion does not address the position of
Ornithopodichnus or Jiayinosauropus already known when
this interpretation was proposed. For this reason Lockley et al.
(in press) have reviewed the ichnotaxonomic status of Creta-
ceous ichnotaxa attributed to ornithopods and find that the sug-
gestions of Lucas et al. (2011) are in need of re-evaluation.
Although reiterating the conclusions of this review is beyond
the scope of this study, Ornithopodichnus is an ichnotaxon of
undoubted ornithopod affinity, which must be considered in
any comprehensive review of this group of trackmakers. If the
ichnogenus proves to be exclusively or dominantly of Asian
affinity, as suggested in preliminary reports, it may support the
inference that Lower Cretaceous ichnofaunas from Asia are
regionally distinctive (Lockley et al., 2012b). If this is the
case the single, global Lower Cretaceous biochron of Lucas
(2007) may potentially be differentiated and defined in more
detail.
ACKNOWLEDGMENTS
The authors thank Hendrik Klein (Saurierwelt
Pal
aontologisches Museum, Germany) for his critical com-
ments and suggestions on this paper; EBI JieFang (Zhaojue
County Bureau of Culture, Multimedia, Press & Sport Tour-
ism, Zhaojue, China), LIU Jian and JIANG Jun (Sichuan
Mountaineering Association, China) for their participation in
field research. The detailed revisions by Hendrik Klein and
Ignacio D
ıaz-Mart
ınez, and the Associate Editor Christian
Meyer greatly improved the final version and we are appre-
ciative of their efforts.
FUNDING
This work was supported by the special projects grants of
Zhaojue County People’s Government.
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222 L. XING AND M. G. LOCKLEY
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... The track is symmetrical and appears to represent a small ornithopod, based on its small size (10 cm in length), low length/width ratio (1.0), and relatively wide divarication angle (76 ), weak anterior triangle length/width ratio (0.37). Small-sized ornithopod tracks from China mainly include EarlyeMiddle Jurassic Anomoepus (Xing et al., 2021c), or Cretaceous Ornithopodichnus (Xing and Lockley, 2014). The CU 214.91 is similar to Anomoepus-like forms compared to the Ornithopodichnus. ...
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