Tracking Lower Cretaceous Dinosaurs in China: a newdatabase for comparison with ichnofaunal data fromKorea, the Americas, Europe, Africa and Australia
MARTIN G. LOCKLEY1*, LIDA XING2, JEONG YUL KIM3 and MASAKI MATSUKAWA4
1Dinosaur Trackers Research Group, University of Colorado Denver, CB 172, PO Box 173364,Denver, CO 80217-3364, USA2School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China3Department of Earth Science Education, Korea National University of Education, Cheongwon,Chungbuk 363-791, Korea4Department of Environmental Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
Received 1 February 2014; revised 11 March 2014; accepted for publication 12 March 2014
Following the recent rapid increase in the reports of tetrapod tracksites in the Cretaceous, especially from theLower Cretaceous, of China and other parts of East Asia, notably South Korea, a review of the ichnofaunaldatabase from these regions is presented as the basis for comparisons with other Lower Cretaceous ichnofaunasthat are abundant and reasonably well documented. These areas include parts of North and South America,especially the western USA, and parts of Europe, including the United Kingdom, Northern Germany, Spain, Italyand Croatia. The Chinese database presently includes about 70 Cretaceous sites, the majority of which are EarlyCretaceous in age. Although abundant data are available from many regions, much of it has yet to be synthesizedin detail or in standard formats. Moreover, ichnotaxonomy may be variable (provincial) between different regions.Thus, while comprehensive lists of sites are available for some regions (China and South America), in other regionssuch as South Korea and the western USA data have been compiled primarily on a formation by formation basis.The record for Europe is moderately good, but scattered in the primary literature and in need of further synthesis.The record for Australia and Africa is sparse and also in need of synthesis. The most notable regional differencesbetween ichnofaunas appears to be in the relative abundance of distinctive bird and pterosaur track ichnotaxain China and Korea in comparison with their scarcity or absence in other regions. The distinctive ichnogenusMinisauripus is also known only in China and Korea as are the majority of known dromaeosaurid trackoccurrences. Ornithopod-dominated and ornithopod-rich ichnofaunas are widespread and particularly abundant inthe late Early Cretaceous Barremian to Albian, of some regions. Most well documented Early Cretaceousichnofaunas are associated with siliciclastic facies and evidently differ from those associated with carbonatefacies. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789.
ADDITIONAL KEYWORDS: China – Cretaceous – dinosaurs – footprints – tetrapods.
INTRODUCTION
In this paper we review what is currently known ofdinosaur and other tetrapod tracksites in the EarlyCretaceous of China and other footprint-rich regionsincluding Korea, the Americas and Europe. Due tovariability and limitations in available databases,
only brief discussion of African and Australian trackrecords is possible. It is well known that the rate ofdiscovery of dinosaurs, both avian and non-avian, inChina has been impressive in recent years, due notleast to the steady increase in reports of feathereddinosaurs from northeastern China. The majority ofthese come from the Yixian Formation, which isessentially devoid of footprints, evidently becausethe facies is unsuitable for footprint registration(see Matsukawa et al., 2014). However, this does not*Corresponding author. E-mail: [email protected]
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Biological Journal of the Linnean Society, 2014, 113, 770–789. With 3 figures
© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789770
mean that tracksites are rare in the Early Cretaceousof China. On the contrary, we now know of about 70sites reported from most of the 31 provinces, regionsand municipalities of China. Here we summarize thedata available from these sites and compare theresults with summaries derived from other areaswell-known for abundant Early Cretaceous tracksitesincluding Korea, North and South America andEurope. We also discuss the differences between data-bases obtained from different regions by differentmethods.
Impetus for the present study derives from severalsources. First, it is a contribution to the Jehol-Wealden International Conference, held in Englandin September 2013 (see acknowledgements). Second,is the opportunity to showcase the rapid developmentof Early Cretaceous tetrapod ichnology in China inthe last decade. Third, the study provides an oppor-tunity to compare the most important Early Creta-ceous ichnofaunas from China with those known fromother parts of East Asia, the Americas, Europe andelsewhere. As discussed, these databases are veryvariable and incomplete in some regions.
PREVIOUS WORK
The first attempts to summarize the fossil footprintrecord of China, in the English literature, was byZhen et al. (1989, fig. 19.1) who identified a total of 22‘principal dinosaur footprint localities’ of which onlyeight were reported as being Cretaceous in age. Thisnumber was more than doubled when Matsukawa,Lockley & Li (2006) reported 52 principal sites fromChina, including 29 in the Cretaceous, as well as anadditional 20 mostly Cretaceous sites elsewhere inEast Asia. Between 1999 and 2006, much of this workwas spear-headed by two of the present authors (MGLand MM) culminating in short reviews (e.g. Lockley &Matsukawa, 2009). Presently this work is being con-tinued (2007-present) under the leadership of LX andMGL, with continued participation by the otherauthors. As noted below these lists are always under-estimates, and always in need of updating. This isbecause they often deal only with principal sites, ortreat previously defined tracksite regions, whereseveral discrete sites occur in close proximity, assingle sites. Efforts to list tetrapod tracksites inChina and East Asia have been fairly consistent, atleast in style of presentation. The map produced byZhen et al. (1989) formed the basis of subsequentmaps (Matsukawa et al., 2006; Lockley et al., 2012a)and is again used here (Fig. 1). However, as notedabove, the number of tetrapod tracksites reportedfrom China has increased rapidly in recent years andis now in excess of 100, with about 70 being knownfrom the Cretaceous (Table 1). There have been recent
efforts to simplify the ‘over-split’ ichnotaxonomy ofChinese tetrapod tracks (Lockley et al., 2013). Oneoutcome of this study has been to conclude thatJurassic tetrapod ichnotaxonomy was even more over-split than Cretaceous ichnotaxonomy. Nevertheless34 Chinese tetrapod ichnospecies have been named todate (Lockley et al., 2013, Table 1; Table 1 herein). Asnoted in the following sections work on importanttracksites in Korea, the Americas and Europe hasbeen ongoing at least since the 1980s, if not earlierin some regions. However, due to the difference insize of study areas, geology and research methods(traditions), the emergent data have proved quitevariable.
MATERIAL AND METHODS
Despite the aforementioned studies that review thedistribution of ichnofaunas in China and East Asia,the potential data base is vast, especially when com-parative data from Korea, the Americas and Europe isincluded. Ideally a complete database should includea list of all sites, and the number of track types andtrackways reported from each. While such data areavailable for some sites, reliable data are by no meansreadily available for all sites. This is to say nothing ofthe variability employed in naming various trackmorphotypes either at the ichnospecies, ichnogenus orless-precise higher taxonomic levels. Moreover thepublished record is always in need of re-evaluation,as some sites are enlarged, others removed or dimin-ished by erosion or human impact, and yet othersre-evaluated by re-naming or re-surveying thevarious ichnotaxa, and their relative abundance. Withincrease interest in geoheritage studies, and the crea-tion of national and international geoparks and WorldHeritage sites in areas with significant fossil footprintsites, efforts are underway to find consistent methodsfor evaluating the importance of tracksites, becausesuch comparative analyses are required for suchnominations and designations. Thus, several studies,pertaining to World Heritage site nominations havecreated lists of the globally most important tetrapodtracksites based on a number of factors: size of site,number of trackways, diversity of track types, pres-ervation quality, and other features. These factorscannot be discussed in detail here. However, it isimportant to note that many factors must be consid-ered in measuring importance, including those listedabove. These factors may be of similar or differentimportance in evaluating sites for scientific study andfor geoheritage designations. For example, large sitesmay appear high on the global list of importance,whereas small sites do not. Nevertheless, small sitesmay be of scientific significance and it is important toinclude all sites in databases if possible.
DISTRIBUTION OF EARLY CRETACEOUS DINOSAUR TRACKS 771
© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789
Tab
le1.
Lis
tof
72te
trap
odtr
acks
ites
from
Ch
ina,
refe
rred
toas
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tace
ous
inat
leas
ton
epu
blis
hed
sou
rce.
Not
eth
atso
me
may
beas
soci
ated
wit
hth
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rass
ic–C
reta
ceou
sbo
un
dary
and
som
em
aybe
Upp
erC
reta
ceou
sin
age.
Hol
otyp
eoc
curr
ence
sal
son
oted
(lig
ht
gree
nsh
adin
g;li
ght
grey
inpr
int)
.T
her
o,th
erop
od;
sau
ro,
sau
ropo
d;or
nit
h,
orn
ith
iosc
hia
n;
pter
o,pt
eros
aur;
croc
,cro
codi
lian
Sit
eP
rovi
nce
Age
Fm
orG
pT
her
oB
ird
Sau
roO
rnit
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tero
Cro
cTu
rtle
Hol
otyp
e
1To
ngf
osi
Jili
nC
ret
Ton
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ix
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ith
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arly
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nn
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x17
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nn
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xx
18Y
uan
jiat
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4Y
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nan
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23G
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ong
Sic
hu
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arly
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nge
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s24
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mei
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hu
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XX
XX
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llat
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sis,
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inis
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hab
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chu
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x38
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arly
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x39
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abu
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lE
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suE
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up
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San
gpin
gX
772 M. G. LOCKLEY ET AL.
© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789
52Ya
ngm
eike
ng
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ando
ng
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pod
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sis
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onin
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arly
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tY
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nx
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jin
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liu
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s67
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x73
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pule
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lila
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nan
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s,S
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pus
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shou
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i77
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shu
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ng
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n78
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x79
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ings
han
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ando
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nji
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xx
81L
ish
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x82
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ua
xx
xx
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ush
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uan
don
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ate
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tN
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ong
x86
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enko
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un
nan
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ret
Pu
chn
agh
ex
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89S
anbi
luog
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ret
Fei
tian
shan
xx
xx
90Je
ufa
ngg
ouS
ich
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ret
Fei
tian
shan
x91
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gmoz
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ich
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lyC
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Fei
tian
shan
x95
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us
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hu
anE
arly
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tJi
agu
anX
?x
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arir
ich
niu
mlo
tus,
Wu
pus
agil
is96
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yuan
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hu
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arly
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agu
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98Yo
ngn
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eilo
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ian
gE
arly
Cre
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ng’
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nx
Jia
yin
osau
ripu
sjo
hn
son
i99
Ch
abu
10N
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arly
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anch
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hab
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Mon
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Ch
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12N
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arly
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anch
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hab
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Mon
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chu
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103
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anch
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DISTRIBUTION OF EARLY CRETACEOUS DINOSAUR TRACKS 773
© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789
As noted above, researchers studying Chinese tetra-pod tracksites have been relatively consistent incompiling lists of tracksites, often with precise GPScoordinates, name of track-bearing unit (formation orgroup) and comments on the track types present,especially holotypes: see, for example, the appendix of52 Chinese sites provided by Matsukawa et al. (2006pp. 19–20). However, the number of trackways ofany given type has not been reported for many ofthese sites, and may not be precisely known from theprimary literature. Nevertheless, for consistency, thecurrent updated list of Chinese sites is based on asignificant expansion of the 2006 list, and also includesformation or group name, and reference to holotypesand known track types. In order to protect sites GPSinformation is not published here, although it may
appear in other publications and be obtainable fromthe authors for bona fide research purposes. Suchconsistency makes comparative study easier, allowingus to compare Chinese sites with those from otherregions, from which comprehensive data are available.These regions, in approximate order of publicationinclude South America (Leonardi, 1989, 1994), NorthAmerica (Lockley et al., 2006a, 2010a) South Korea(Lockley et al., 2006a, 2012a, b; Lockley, Huh & Kim,2012c) and Europe. Lockley et al. (2012a) also compileda list of all significant Cretaceous tracksites, but didnot number the sites, or break them down into regionalgroupings. The methods used in compiling data,the geographical areas included in the studies, and thestratigraphic precision with which they have beenrecorded are summarized as follows.
Figure 1. Mesozoic tetrapod tracksites in China. Note separate symbols for Triassic, Jurassic and Cretaceous sites. Todate the present authors have recorded at least 106 Mesozoic sites. About 70 of these are Cretaceous in age (see Table 1).Precise dating is not available for all sites. Thus, differentiating which sites are just above or below the Jurassic–Cretaceous and Lower to Upper Cretaceous boundaries is difficult in some cases.
774 M. G. LOCKLEY ET AL.
© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789
South Korea is a relatively small area in compari-son with neighboring China, and the track-bearingregions of North and South America discussed below.Nevertheless it has yielded hundreds of tracksitessince the first were reported in the early 1980s.One of the distinctive features of the Korean sitesis that many occur in close proximity at differentstratigraphic levels in small geographical areas. Forexample Lockley et al. (2006b) compiled measure-ments for ∼300 individual dinosaur trackways fromseveral hundred horizons in the Jindong Formation atfour named locations within the Goseong Tracksite, ageographic stretch of coastline only about 3 km long(see Houck & Lockley, 2006: table 2 here). This, com-pilation was exclusive of dozens of bird tracks from atleast 30 horizons identified in the same outcrops. Asnoted below, this type of data is comparable with dataobtained from single track-rich formations in otherregions. However, in the case of Korea it is only partof the picture as there are many other tracksites inother Cretaceous formations throughout the wholecountry.
The work of Leonardi (1989, 1994) is truly conti-nental in scope and his data is comparable in scaleand stratigraphic range to the compilations reportedfor China. Leonardi (1989) reported 28 principal Cre-taceous tracksites of which 23 are identified as EarlyCretaceous. This number was considerably increasedin a more detailed compilation (Leonardi, 1994) whichreferred to about 38 sites. In this latter publicationmap locations and approximate coordinates, forma-tion names and track types were given for all sites,and individual trackways were counted in manycases. As noted below, it has been possible to updatethe data of Leonardi (1994) by adding informationfrom a number of new Cretaceous tracksite reportspublished during the last 2 decades.
By contrast, the data available for North Americaare of a different order. The most comprehensivecompilations of data currently available are forvarious track-rich formations that have been inten-sively studied. For example, Lockley et al. (2010a)compiled the number of track types and trackwaysfrom 70 ‘Mid’ Cretaceous Dakota Group tracksiteseast of the continental divide in Colorado, NewMexico, Kansas and Utah. Recently, this number wasincreased to 80, and an additional 40 sites have beenreported from west of the Continental Divide (Lockleyet al., 2014a). Likewise Pittman (1989) reported 42tracksites from the Comanche Series of Texas, mostlyfrom the well known Glen Rose Formation. Thenumber of track types and trackways recorded frommany of these sites, as well as additional sitesreported since 1989, is known from scattered litera-ture sources but such data have not been compiledinto a coherent database. Finally, any reference to
Cretaceous tetrapod tracksites from North Americamust include reference to the abundant, sitesreported from western Canada. These are scatteredgeographically as well as stratigraphically (McCreaet al., 2014).
RESULTSEARLY CRETACEOUS TETRAPOD
ICHNOFAUNAS IN CHINA
As shown in Table 1, ∼70 tetrapod tracksites localities(locs.) are known from the Cretaceous of China, andto date have been identified from all but four prov-inces (the exceptions being Qinghai, Guangxu, Fujianand Hubei: see Fig. 1). The precise age of many for-mations is uncertain, according to primary sources.Nevertheless, in most cases age determinations orestimates exist in the literature and are used here. Asexpected the distribution of geological formationscauses some areas to have higher concentrations oftracksites. Likewise the variation in age, facies andichnological content of these formations results insignificant variation in track types and significance oftracksites in different regions. For these reasons, wefocus attention on the more important tracksiteregions (C1–C6) and track-bearing units as follows:
C1: Northeastern China. This region is historically impor-tant for having produced some of the first named dinosaurtracks from China. These include Grallator ssatoi (formerlynamed Jeholisauripus s satoi) an abundant small theropodtrack from the Tuchengzi Formation (Yabe, Inai & Shikama,1940; Matsukawa et al., 2006) in Liaoning Province. This unitis currently considered to represent the Jurassic-Cretaceous(Tithonian-Berriasian) transition, and thus may include someof the oldest Cretaceous ichnofaunas in Asia (locs. 2–4 ofFig. 1), for example bird tracks (Pullornipes aureus) reportedby Lockley et al. (2006c) may be among the oldest known fromAsia. Saurischian tracks occur in this formation elsewherein the region including Hebei Province (Xing et al., 2009a;Xing, Harris & Gierlinski, 2011a) and the Beijing Municipal-ity, where sauropod tracks also occur in the recently desig-nated Yanqing International Geopark (loc. 54) (Zhang et al.,2012).
C2: Shandong Province. Tetrapod tracks were first reportedfrom Shandong province by Young (1960) who namedLaiyangpus liui from the Shuinan Formation (loc 10), andmistakenly assigned it to theropod dinosaur, when it is likelyof crocodile affinity (Lockley et al., 2010b). Since 1960, othertracks found at the site include bird tracks (ichnogenusTatarornipes: Lockley et al., 2011). Small theropod tracks arealso abundant in Shandong including the problematicichnotaxon Paragrallator yangi (cf. Grallator), from loc. 9, andhave been found at most of the other localities known in theprovince (Fig. 1). The most important localities reported todate include the Junan site (loc. 76) which has yielded a highdiversity of forms from multiple levels in the Tianjialou
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Formation, which is thought to be Barremian-Aptian in age.These include both large and small dromaeosaur tracks,Dromaeopodus and Velociraptorichnus respectively (Li et al.,2007, 2014), highly distinctive small theropod trackMinisauripus (Lockley et al., 2008), the unique roadrunner-like track Shandongornipes (Lockley et al., 2007) and moretypical bird tracks (Koreanaornis). Ornithopod tracks alsooccur at this site. Recent studies of other Tianjialou tracksitesin the region report other dromaeosaur tracks, sauropodtracks and possible psittacosaur tracks (Xing et al., 2013a).Another very important site occurs at Huanglongou (YellowDragon Valley) in the Lower Cretaceous LongwangzhuangFormation near Zhucheng, here (loc. 75) more than 2000tracks have been mapped on a single surface including abun-dant Grallator tracks, the distinctive theropod trackCorpulentapus (Li et al., 2011b; Lockley et al., 2012d), sauro-pod tracks and some of the first turtle tracks reported fromChina (Lockley et al., 2012e). Pterosaur tracks have also beenreported from the Qugezhuang Formation (Xing et al., 2012).Collectively the above-listed Shandong sites have yieldedamong the most diverse ichnofaunas reported from theChinese Lower Cretaceous.
C3: Inner Mongolia. The Ordos Basin region of Inner Mon-golia (Nei Mongol) has yielded at least 17 tracksites (locs.36–44 and 99–105) in the Chabu region near Otog Qi (Liet al., 2009; Li, Bai & Wei, 2011a). These occur mainly in theJianchuan Formation and include assemblages dominated bysaurischian tracks including the non-avian theropod tracksChapus and Asianopodus (Li et al., 2006, 2011a respectively),the sauropod track Brontopodus (Lockley et al., 2002) and thebird (avian theropod) track Tatarornipes (Lockley et al., 2011).
C4: Gansu Province. A number of tracksites have beenreported from the Hekou Group in the Yellow River (HwangHe) valley near Lanzhou in Gansu Province. The two largestsites occur side by side at Yangouxia National Geopark (loc.50). They reveal a remarkable diversity of track types includ-ing tridactyl and didactyl theropod tracks, the latter repre-senting the first reported Dromaeosauripus from China (Xinget al., 2013b), unusually large sauropod tracks, ornithopodtracks, pterosaur tracks (Pteraichnus) which were the firstreported from China (Peng et al., 2004; Zhang et al., 2006) andbird tracks (cf. Aquatilavipes).
C5: Sichuan Province and Chongqing City. Until recentlythe Xingfu Cliff site in Emei County has been regarded as oneof the best known and most important Cretaceous tracksitesin China. It is a very small site (Loc. 24), but it has yielded thetype material for the well known ichnogenera Minisauripusand Velociraptorichnus, as well as new ichnospecies ofAquatilavipes and Grallator (Zhen, Li & Zhang, 1994) Theichnogenus Iguanodonopus has been declared a nomendubium. (Xing et al., 2009b; Lockley et al., 2013). In contrastto the Emei County site, new tracksites in the Zhaojue areareveal very large surfaces associated with large copper mineexcavations. These sites reveal with very long trackways oftheropods, sauropods, ornithopods and a few pterosaurs. TheLotus site in the Qijiang area (Chongqing City) is also a largetracksite associated with a historically famous cliff fortress. It
has yielded well preserved quadrupedal Caririchnium, andthe bird-like track Wupus (Xing et al., 2007) and pterosaurtracks (Xing et al., 2013c). The Sanbiluoga site in the ZhaojueCounty also reveals theropod, sauropod ornithopod and ptero-saur tracks (Xing et al., 2013c), including the first definitivenon-avian theropod swim trackway from China (Xing et al.,2013d).
C6: Xinjiang Autonomous Region China. Xinjiang is ahuge region of western China that remains largely unexploredfor its tetrapod tracks potential (Fig. 1). However in recentyears two important tetrapod tracksites have been describedfrom the region. The first, the Wuerhe site has yielded adiverse assemblage of non-avian and avian theropod,thyreophoran (Deltapodus), pterosaur and turtle tracks. Thisis first record of Deltapodus from the Cretaceous of China(Xing et al., 2013e). The second, the Asphaltite site also yieldsnon-avian and avian theropod tracks together with pterosaurtracks (He et al., 2013; Xing et al., 2013f). The area has hugepotential for more tracksite discoveries.
EARLY CRETACEOUS TETRAPOD
ICHNOFAUNAS IN KOREA
Since the discovery of Cretaceous dinosaur tracks inKorea in the early 1980s (Yang, 1982) the rate ofreport of diverse tetrapod ichnofaunas, all pertain-ing to the Cretaceous, has increased rapidly. In factthe abundance of sites, especially at localities alongthe southern coast has led to the concept of theKorea Cretaceous Dinosaur Coast (KCDC). Probablythe most accessible summaries of the many discov-eries since 1982 are found in the special issue ofIchnos, vol. 19 (1–2), entitled Tracking on theKorean Cretaceous Dinosaur Coast: 40 years of ver-tebrate ichnology in Korea (Lockley et al., 2012b)and the Mesozoic terrestrial ecosystems of theKorean Cretaceous dinosaur coast: a field guide tothe excursions of the 11th Mesozoic Terrestrial Eco-systems Symposium (Lockley et al., 2012c). Lee et al.(2000) also provided summary information onKorean dinosaur tracksites.
As is the case in China, many of the Cretaceousdeposits in Korea have proved difficult to date, partlybecause of the widespread effects of thermal andregional metamorphism (Houck & Lockley, 2006).However, we may summarize the present state ofknowledge as follows. The majority of track-bearingdeposits have been reported from the GyeongsangSupergroup of the Gyeongsang Basin which occupiesmuch of the southeastern sector of the Koreanpeninsula (Fig. 2). The Gyeongsang Supergroup isdivided into three groups: the predominantly sedi-mentary lower and middle groups, the Sindong andHayang Groups respectively, which succeed eachother conformably and the upper, predominantlyvolcanic Yucheon Group which overlies the older
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sequences unconformably. Recent literature hasdated the track-rich Sindong and Hayang Groups asHauterivian to Albian (Houck & Lockley, 2006) or assomewhat younger, Aptian to Campaninan (Paiket al., 2012). In the southwestern sector of the Koreanpeninsula there are a number smaller basin withtrack-rich deposits, that have tended to yield LateCretaceous dates, but many of the stratigraphicsequences in this area remain unnamed.
In recent years tetrapod tracks from the regionhave become very well-known. As indicated inTable 2, there have been relatively few importanttracksites reported from the older Sindong Group,which has however, yielded some tetrapod body fossils(Fig. 2A). The more significant reports include theoldest Korean report of pterosaur tracks (Pteraichnus,Lee et al., 2008) from the Hasandong Formation andthe oldest Dromaeosauripus from the Jinju FormationKim et al. (2012a). However, the vast majority ofsignificant tracksites has been reported from the over-lying Hayang Group, much of which is made up of thetrack-rich Haman and overlying Jindong Formationsusually dated as Aptian-Albian (Houck & Lockley,2006). As indicated in Table 2 and the aforementionedsummary publications (Lockley et al., 2012b, c)the Haman Formation has yielded six tetrapodtrack holotypes attributable to avian and non-aviantheropods, sauropods and pterosaurs. These areassigned to the avian ichnogenera Koreanaornis(Kim, 1969), Ignotornis (Kim et al., 2006; Kim et al.,2012b), dromaeosaurids (Dromaeosauripus Kim et al.,2008), sauropods (Brontopodus) (Kim & Lockley,2012) and pterosaurs (Haenamichnus) (Kim et al.,2012c). The Haman Formation has also produced arelatively large number of reports of the smalltheropod ichnogenus Minisauripus (Lockley et al.,2008; Kim et al., 2012d), which is currently onlyknown from the Cretaceous of China and Korea.
The Jindong Formation is perhaps even richerin tracks than the Haman Formation. The south-western part of Goseong County referred to as theSamcheonpo tracksites (Fig. 2B) is also designatedas Korea Natural Monument 411, and is alsoreferred to as the Goseong Tracksite, although it isone of many tracksite areas in Goseong County. Inthis area (Monument 411) hundreds of track-bearinglevels have been documented in great detail (Lockleyet al., 2006b; Houck & Lockley, 2006). Several aviantheropod (bird) holotypes have been named andassigned to the ichnogenera Jindongornipes (Lockleyet al., 1992), Goseongornipes (Lockley et al., 2006b)and Gyeongsangornipes (Kim et al., 2013). In addi-tion the ornithopod ichnogenus Ornithopodichnus(Kim et al., 2009) is from the Jindong Formation. Formore information on bird tracks see Lim et al. (2000,2002).
There are a number of other important tetrapodtracksites in the Cretaceous of Korea, including three,like the Goseong area, which are designated as KoreaNatural Monuments 394, 434 and 487. All three ofthese sites have been reported as Upper Cretaceousin age, or of uncertain age, and so are not includedhere in Table 2. Briefly they are as follows: NaturalMonument 394 is the Haenam Tracksite whereornithopod (Caririchium) pterosaur (Haenamichnus)(Lockley et al., 1997) and bird tracks (Hwangsanipesand Uhangichnus) occur in the Uhangri Formation.The latter tracks show traces of a fully developedinterdigital web and are convergent with small ducks(Yang et al., 1995; Lockley & Harris, 2010). NaturalMonument 434 is the Yeosu Tracksite associated withan unnamed formation yielding theropod, sauropodornithopod and bird tracks (Huh et al., 2012; Lockleyet al., 2012b, c, f, g). The Hwasun tracksite, NaturalMonument 487 yields theropod, sauropod andornithopod tracks from the Jingdong Tuff (Huh et al.,2006; Lockley, Huh & Kim 2012c, h).
Although other tracksites occur in elsewhere insoutheast Asia, they are not abundant. For example,Matsukawa et al. (2006) reported only nine tracksitesfrom Japan and five from Thailand, and this numberhas not increased significantly as a result of newreports. However, it is worth noting that some ofthese ichnofaunas contain named ichnotaxa that arenot reported from other ichnofaunas discussed here.For example, the distinctive theropod ichnogenusSiamopodus (Fig. 3) is currently known only fromThailand (Lockley et al., 2006d), and small theropodichngenus Toyamasauripus is known from Japan.Asianopodus, also a theropod ichnogenus, originallybased on a Japanese holotype (Matsukawa et al.,2005), is also abundant at some sites in Thailand. Theonly known Cretaceous report of Batrachopus isalso from Thailand (Le Loeuff et al., 2010), as is theonly known Asian report of Neoanomoepus (Lockley,McCrea & Matsukawa, 2009). Most other dinosaurtracksites from Japan and Thailand have yielded onlysmall assemblages of theropod and ornithopod tracksfew of which have been named. Sauropod tracks occurat one locality in Laos (Matsukawa et al., 2006).
EARLY CRETACEOUS TETRAPOD ICHNOFAUNAS IN
SOUTH AND CENTRAL AMERICA
It is outside the scope of this review to outline the workof Leonardi (1989, 1994) in detail. Initially, in 1989 hereported 23 Cretaceous sites, increasing this numberto 38 in a later compilation (Leonardi, 1994). Themajority of these (about 28) are Lower to Mid-Cretaceous in age His continent-wide survey is com-parable to the compilation presented here for Chinawhich identified 105 tracksites. In the case of South
DISTRIBUTION OF EARLY CRETACEOUS DINOSAUR TRACKS 777
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778 M. G. LOCKLEY ET AL.
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and Central America Leonardi (1994) identified 115sites including 88 that are reported as Mesozoic in age.Since 1994 approximately 16 Cretaceous sites havebeen added for a total of about 54 sites: data weretaken from Lockley et al. (2012a) and other sources.Approximately ten of the newly added site are Loweror Mid-Cretaceous in age, giving an estimated total ofabout 38 Lower to ‘Mid’ Cretaceous sites.
The largest concentration of Early Cretaceous sitesis in the Sousa Basin of Brazil, where Leonardi (1994)listed 18 sites. All but one reveal theropod tracks withseven sites yielding ornithopod tracks, including theimportant type specimen of ichnogenus Caririchnium(Leonardi, 1984) which has been widely identifiedon other continents, and five sites also yielding sau-ropod tracks. None of the other sites shows stronggeographical concentrations or highly distinctiveichnofaunas. Bird tracks are conspicuous by theirabsence in the Lower Cretaceous although there arethree reports from the Upper Cretaceous (Lockley &Harris, 2010). Pterosaur tracks are also scarce (Calvo& Lockley, 2001).
EARLY CRETACEOUS TETRAPOD ICHNOFAUNAS
IN NORTH AMERICA
Important Early Cretaceous tetrapod ichnofaunasfrom North America are mostly known from thewestern USA and western Canada. In both regionsthere are major gaps in the Neocomian successions,leaving only the Aptian and Albian well represented.Only one significant ichnofauna is known fromthe eastern USA containing a diverse assemblageof mostly small tracks of theropods, ornithopods,sauropods and pterosaurs (Stanford, Lockley &Weems, 2007) from the Aptian Patuxent Formation.The size-frequency of the track assemblage is biasedby the unusual preservation in small pieces ofreworked sediment. In the western USA the oldestsignificant in situ assemblages are those reportedfrom the Cedar Mountain Formation (Aptian-Albian)of eastern Utah. Relatively few sites are known butthey show a high diversity of tracks attributedto birds (Aquatilavipes) and non-avian theropods(Dromaeosauripus and Irenesauripus), sauropods(Brontopodus) and ornithischians (Caririchnium andDeltapodus) (Lockley et al., 2014a, b).
In contrast to the diverse Patuxent and CedarMountain ichnofaunas associated with clastic fluvio-
lacustrine facies, the Albian Glen Rose Formationichnofaunas occur in carbonate platform sequences inTexas. These were described by Pittman (1989) asdominated by ichnites of large, theropods, attributedto Acrocanthosaurus, (Farlow, 2001) and large widegauge (Brontopodus) trackways described in somedetail by Farlow, Pittman & Hawthorne (1989) andattributed to titanosauriform sauropods.
Again in contrast to the Texan ichnofaunas theslightly younger (Late Albian-Cenomanian) track-richsiliciclastic, coal-bearing facies of the Dakota Groupis rich in ornithischian tracks, and apparently devoidof sauropod tracks, despite reports of at least 120sites (Lockley et al., 2014c). This lack of sauropodevidence is apparently due to facies differences andwhat has been referred to as the North American‘sauropod hiatus’ (Lucas & Hunt, 1989) beginning inthe Late Albian. The dominant ornithischian tracksare of ornithopod affinity (Caririchnium) especially ineastern Colorado and northeastern New Mexico,but ankylosaur tracks (Tetrapodosaurus) are morecommon in western Colorado. Theropod tracks, espe-cially Magnoavipes, probably representing a gracileornithomimid, are moderately common, and crocodil-ian swim tracks (Hatcherichnus) are also common.Bird tracks (Ignotornis and Koreanaornis) are rare(Mehl, 1931; Lockley & Harris, 2010), but tracks ofsmall and large pterosaurs (cf., Pteraichnus) are mod-erately common. According to a regional synthesisof more than 1000 trackways from ∼70 Dakotatracksites (Lockley et al., 2010a, table 6), across thethen-known eastern outcrops the dominant tracktype is Caririchnium, representing ornithopodtrackmakers. This ichnogenus outnumbers all othertracks types by an order of magnitude (i.e. by at least10:1, or more). Preliminary study of at least 40tracksites across the western outcrops indicates thatthe ornithopods were far less dominant and thatankylosaur trackmakers were common (Lockley et al.,2014c).
While the ichnofaunas from the four stratigraphicunits outlined above (Patuxent, Glen Rose, CedarMountain and Dakota) are representative of well-studied and locally or regionally track-rich depositsfrom the lower 48 states of the USA, many othertrack-rich Cretaceous deposits are known fromwestern Canada. These were recently reviewed byMcCrea et al. (2014). It is outside the scope of thispaper to discuss these ichnofaunas in detail.
Figure 2. Aspects of the stratigraphy and distribution of tracksites in the Cretaceous of Korea. A: the main track-bearingformations in the Sindong and Hayang Groups Gyeongsang Basin. Note that the age of these formations is debatedin the literature (see text for details). B: distribution of tracksites in Goseong County, with special reference to theSamcheompo tracksite also designated as the Goseong Tracksite and Korea Natural Monument 411. Compare withTable 2.◀
DISTRIBUTION OF EARLY CRETACEOUS DINOSAUR TRACKS 779
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Tab
le2.
Dis
trib
uti
onof
Ear
ly(–
‘Mid
’)C
reta
ceou
str
ack
type
sin
mai
nu
nit
sof
the
Sin
don
gan
dH
ayan
gG
rou
ps(G
yeon
gsan
gB
asin
)K
orea
,w
ith
asso
ciat
edh
olot
ype
occu
rren
ces.
Th
ero,
ther
opod
;sau
ro,s
auro
pod;
orn
ith
,orn
ith
iosc
hia
n;p
tero
,pte
rosa
ur;
croc
,cro
codi
lian
.Not
eth
attr
acks
ite
occu
rren
ces
inot
her
basi
ns,
wh
ere
purp
orte
dU
pper
Cre
tace
ous
trac
ksar
ere
port
ed,
are
not
incl
ude
d.S
eete
xtfo
rde
tail
s
Sit
eor
sect
ion
Age
Str
atu
nit
Trac
kle
vels
Th
ero
tway
sB
ird
tway
sS
auro
tway
sO
rnit
ho
tway
sP
tero
tway
sH
olot
ypes
Ref
eren
ce
Gos
eon
g1
Sil
baw
iE
arly
Cre
t.Ji
ndo
ng
651
n20
14L
ockl
eyet
al.,
2006
bG
oseo
ng
2B
ongw
hag
olE
arly
Cre
t.Ji
ndo
ng
17n
617
Loc
kley
etal
.,20
06b
Gos
eon
g3
Dek
mye
ong-
riE
arly
Cre
t.Ji
ndo
ng
792
n31
76J
ind
ongo
rnip
eski
mi
Gos
eon
gorn
ipes
mar
kjon
esi
Geo
ngs
ango
rnip
eslo
ckle
yi
Loc
kley
etal
.,19
92,
Loc
kley
etal
.,20
06b,
Kim
etal
.,20
13
Gos
eon
g4
San
gjok
Ear
lyC
ret.
Jin
don
g57
1n
3892
Kim
etal
.,20
13G
oseo
ng
5D
ongh
ae-m
yeon
Ear
lyC
ret.
Jin
don
g6
428
35L
eeet
al.,
2000
Gos
eon
g6
Hoe
wh
a-m
yeon
Ear
lyC
ret.
Jin
don
g9
139
21L
eeet
al.,
2000
Mas
ansi
teE
arly
Cre
t.Ji
ndo
ng
112
Orn
ith
opod
ich
nu
sm
asan
ensi
sK
imet
al.,
2009
Doc
heo
n-r
iE
arly
Cre
t.Ji
ndo
ng
110
Hw
ang
etal
.,20
04S
ub
tota
lsA
llji
nd
ong
235
9N
172
267
Yon
gsan
-mye
onE
arly
Cre
t.H
aman
NK
orea
nao
rnis
ham
anen
sis
Kim
,19
69
Ch
angs
eon
Isla
nd
Gai
n-r
iE
arly
Cre
t.H
aman
11Ig
not
orn
isya
ngi
Kim
etal
.,20
06S
insu
Isla
nd
Ear
lyC
ret.
Ham
an3
Kim
etal
.,20
06C
han
gseo
nIs
lan
dG
ain
-ri
Ear
lyC
ret.
Ham
an1
12
5H
aen
amic
hn
us
gain
ensi
sK
imet
al.,
2012
c
Ch
angs
eon
Isle
Bu
yun
-ri
Ear
lyC
ret.
Ham
an38
Kim
etal
.,20
12d
Ch
angs
eon
Isla
nd
God
uE
arly
Cre
t.H
aman
5K
imet
al.,
2012
dC
han
gseo
n&
Adu
isle
sE
arly
Cre
t.H
aman
1K
imet
al.,
2012
cC
han
gseo
n&
Ch
uis
les
Ear
lyC
ret.
Ham
an1
Dro
mae
osau
ripu
sh
aman
ensi
sK
imet
al.,
2008
Gaj
in-r
iE
arly
Cre
t.H
aman
1N
=10
0s
2B
ron
topo
du
spe
nta
dac
tylu
s,Ig
not
orn
isga
jin
ensi
s
Kim
&L
ockl
ey20
12
Bit
oIs
lan
dE
arly
Cre
t.Ji
nju
1D
rom
aeos
auri
pus
jin
juen
sis
Kim
etal
.,20
12a
Had
ong
Ear
lyC
ret.
Has
ando
ng
1P
tera
ich
nu
sko
rean
ensi
sL
eeet
al.,
2008
780 M. G. LOCKLEY ET AL.
© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 770–789
However, it is worth noting that the followingichnofaunas are significant and historically impor-tant for the global discussion. First, the CanadianCretaceous contains a number of track-rich unitsassociated with the Jurassic-Cretaceous (Tithonian-Berriasian) transition including the Mist MountainFormation which has yielded a diverse ichnofaunaincluding the Neoanomoepus holotype (Lockley et al.,2009), Canada’s oldest sauropod tracks and variousother dinosaurian and non-dinosaurian tetrapodichnites ranging from large and small non-aviantheropod tracks to probable avian theropod, ptero-saur and aquatic tetrapod swim tracks. Second, theslightly younger (Berriaasian-Valanaginian) GormanCreek Formation also yields a diverse ichnofaunaincluding Neoanomoepus and Tetrapodosaurus.Third, after a significant gap in the Neocomiansuccession the next significant western Canadaichnofauna is that reported from the historicallyfamous Gething Formation (Sternberg, 1932; Currie& Sarjeant, 1979; Currie, 1995; McCrea et al., 2014),which is dominated by tracks of miscellaneous non-avian theropods, ornithischians (type specimens ofAmblydactylus and Tetrapodosaurus) with severalreports of bird tracks (McCrea et al., 2014) includingthe type of Aquatilavipes (Currie, 1981). Forth,
in the Lower Cretaceous succession, a similarichnofauna, with abundant Tetrapodosaurus andavian and non-avian theropod tracks occurs invarious slightly younger units including theearly Albian Gates Formation through the earlyCenomanian Dunvegan Formation (see McCreaet al., 2014 for summary).
EARLY CRETACEOUS TETRAPOD
ICHNOFAUNAS IN EUROPE
As noted above, the impetus for the present studyderives from the Jehol-Wealden International Confer-ence, held in England in September 2013. Ideally itwould have been desirable to have similar databasesfor the two regions, but this is not the case for severalreasons, including the vast size differences inthe regions studied and differences in quality oftracksite exposure. Nevertheless, this contribution,which began with a review of the Lower Cretaceousichnofaunas of China, includes brief reference toLower Cretaceous ichnofaunas from the WealdenGroup in England, and equivalent deposits elsewherein western Europe.
As outlined elsewhere in this volume (Lockley et al.,2014; Lockwood, Lockley & Pond, 2014; Pond et al.,
Figure 3. Distribution of track types in areas with abundant Lower Cretaceous ichnofaunas: C1–C6 refer six areas inChina discussed in text. Kh and Kj respectively refer to the Jindong and Haman Formations of Korea. SA: South America,Pa: Patuxent Fm, eastern USA, Cm: Cedar Mountain Fm, western USA, Tx: Texas, western USA, Dak: Dakota Group,western USA, IW: Isle of Wight, UK. Black square indicate high abundance of a given ichnotaxon or track type; dotsindicate occurrences. Ranges of selected ichnotaxa are given. Modified after Lockley et al. (2012a). Note that exact age ofUK and USA ichnofaunas is well established, but the age of some Asian ichnofaunas is uncertain or in dispute.
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2014) ichnofaunas from the Wealden Group areamong the first ever reported from the Lower Creta-ceous. Historically most reports refer to Iguanodontracks, which appear to be the dominant track type(Lockwood et al., 2014). However, because the rules ofthe International Code of Zoological Nomenclature(ICZN) do not permit use of a genus name based onskeletal material to describe trace fossils, Sarjeant,Delair & Lockley (1998) erected the ichnogenusIguanodontipus, based on relatively small pre-Wealden ichnites from the Purbeck Group (Tithonian-Berriasian). These are significantly different from theBarremian age Wealden Group ornithopod trackswhich have mostly been assigned to Caririchnium.Thus, in essence the Purbeck and Wealden ornithopodfootprints mostly represent the two distinct, respec-tive ichnogenera named above (Lockley et al., 2014).Few other ichnotaxa from the Wealden Grouphave been described in detail, but it appearsthat tracks of theropod, sauropods and otherornithischians (ichnogenera Tetrapodosaurus andpossibly Deltapodus) are also represented.
Ichnofaunas from the Berriasian deposits ofnorthern Germany include unnamed ornithopod(iguanodontid tracks) which resemble Iguano-dontipus (Lockley, Wright & Thies, 2004). Thisichnogenus has recently been identified in rocks ofthe same age in Spain (Castanera et al., 2013),where, like the German tracks a small proportionshow manus prints. It is possible that quadrupedalprogression was less common among Tithonian-Berriasian ornithopods than among larger varietiesrepresented by younger (Barremian-Albian) track-makers. However, we admit that this inference isspeculative. As noted below a recent review byMoratalla & Hernán (2010) of Spanish ichnofaunasfrom the Cameros Basin provides useful data on theproportion of theropod, ornithopod and sauropodtracks found in the Lower Cretaceous (Berriasian)Huérteles Formation and the much younger (Aptian)Enciso Group.
Other Lower Cretaceous tracksites reported fromEurope include those associated with carbonate plat-form paleoenvironments in Switzerland (Meyer &Thuring, 2004), Italy (Sacchi et al., 2009; Pettiet al., 2010) and Croatia (Dalla Vecchia, 2008). Col-lectively these reports deal with quite differentpaleoenvironments from those described from theclastic facies of the Wealden Group and equivalentbeds of England, Germany and Spain. Thus, we cangenerally differentiate between clastic facies in north-ern European and carbonate facies in southernEurope. In the case of the Swiss site from the AlbianSchrattenkalk Formation an iguanodontid trackway,similar to Caririchnium, but not explicitly attributedto that ichnogenus, was reported as an unusual
example of this track type in association with acarbonate substrate, which typically yields theropod-sauropod assemblages characteristic of the Bronto-podus ichnofacies (sensu Lockley et al., 1994). TheItalian sites have yielded a number of trackways ofquadrupedal dinosaurs of uncertain ichnotaxo-nomic affinity. According to Sacchi et al. (2009, fig. 13)theropod, sauropod ornithopod and thyreophoranfootprints are all represented in the Lower Creta-ceous, although in most cases these are all very poorlypreserved, and in our opinion there is no definitiveevidence of ornithopods, or strong evidence to differ-entiate the purported trackways of ankylosaursand sauropods. In this regard the ichnogenusApulosauripus reported by Nicosia et al. (1999) fromUpper Cretaceous carbonates of Italy and attributedto a hadrosaurian track makers, was reinterpreted asbeing of likely ankylosaurian affinity (Gierlinski &Sabath, 2008). Petti et al. (2010) described purportedankylosaur trackway, but again this identification isuncertain. Dalla Vecchia (2008) has identified manytheropod and sauropod tracks from the Lower Creta-ceous of Croatia. Such assemblages are consistentwith the theropod-sauropod assemblage typical of theBrontopodus ichnofacies associated with carbonateplatforms. The combined reports of tracksites fromthese three areas (Switzerland, Italy and Croatia)indicate that tracks are abundant in the Lower Cre-taceous carbonates of the region, as well as in theUpper Cretaceous. However, in general they arepoorly preserved and saurischian (theropod and sau-ropod dominated) with reports of ornithischians(ornithopods and ankylosaurs) generally being eitherrare, uncertain or both.
EARLY CRETACEOUS TETRAPOD
ICHNOFAUNAS IN AFRICA
Relatively few Lower Cretaceous dinosaur tracksitesare known from Africa, although recent studies haveindicated that several sites are known in NorthAfrica, some extending into the ‘Mid’ Cretaceous(Cenomanian). As reported by Bellair & Lapparent(1948) Mid-Cretaceous tridactyl (theropod) trackshave been known from Algeria since 1880. Recentstudies in this region have identified well preservedtheropod tracks of Valanginian age (Bensalah et al.,2005). Other significant Lower Cretaceous sitesinclude those reported from Morocco including atheropod-sauropod tracksite from the Barremian-Aptian Tazought Formation northeast of Agadir(Masrour et al., 2013) and two sites theropod-sauropod tracksites from the Mid-Cretaceous(Cenomanian) Kem Kem Formation (Belvedere et al.,2013; Ibrahim et al., 2014). The former report alsodocuments turtle and crocodilian swim tracks. There
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are a few other reports of confirmed Mid-Cretaceousage including a report of bird tracks from Tunisia(Contessi & Fanti, 2012). Jacobs et al. (1989) reportedwell preserved theropod tracks from Cameroon inWest Africa. Thus, despite recent reports, the Africantrack record for the Early Cretaceous remains verysparse and scattered.
EARLY CRETACEOUS TETRAPOD
ICHNOFAUNAS IN AUSTRALIA
Relatively few tetrapod tracksites are known from theCretaceous of Australia (Long, 1998). Moreover, thefew that are known, although significant, are also verycontroversial making track identification problematic.According to Thulborn (2013) and Thulborn & Wade(1984) the well-known Lark Quarry site, from the ‘Mid’Cretaceous Winton Formation in Queensland, yieldedtwo ichnogenera Wintonopus and Skartopus represent-ing small ornithopods and small theropods respec-tively. Both track types were reported as abundant,and interpreted as evidence of a stampede. Neitherichnogenus has been reported outside Australia.However, according to Romilio, Tucker & Salisbury(2013) these are swim tracks and Skartopus is not avalid ichnotaxon: i.e., it is a junior synonym ofWintonopus. Romilio & Salisbury (2010) also reinter-preted large-theropod tracks as ornithopodan. Thusthere is no consensus on the ichnotaxonomy,trackmaker identity or trackmaker behavior. Tracksfrom the Broome Sandstone in western Australiainclude only one named, uncontroversial ichnogenus,Megalosauropus (Colbert & Merrilees, 1967). Almostall other tracks, although representing unnamedtheropod, sauropod and ornithischian ichnotaxa (Long,1998) are associated with heavily trampled substrates(Thulborn, 2012), and have not been described indetail. Martin, Vickers-Rich & Vazquez-Propkopec(2012) recently described theropod tracks and firstCretaceous bird tracks (Martin et al., 2014) from Vic-toria, Australia. Thus, the entire Lower Cretaceoustrack record from Australia is concentrated in threewidely-separated regions and consists of three named,tridactyl, non-avian dinosaur tracks, including onein dispute, a few avian theropod (bird) tracks andunnamed mostly poorly preserved sauropod andornithischian tracks. Even assuming disputes overtrack interpretation can be resolved, this database isvery sparse in comparison with that available fromother continents.
DISCUSSION
Among the aims of contributions to this volume arecomparison between the Lower Cretaceous faunas of
China and the Wealden Group in England. Compari-sons based on the ichnofaunas of the two regions arepossible, but hampered by various uncertainties. Themost significant problems relate to the uncertain ageof many of the Chinese deposits, due to the complexstructure of Cretaceous basins across China and EastAsia in general (Haggart, Matsukawa & Ito, 2006).Nevertheless, there is no shortage of new ichnologicaldata emerging from China and elsewhere in theregion (notably Korea and Thailand). Given thatthe Wealden ichnofaunas are heavily ornithopoddominated it is easy to a select a few examplesof ornithopod-dominated ichnofaunas, such as theCaririchium -dominated Qijiang ichnofauna (Xinget al., 2007) or the Jindong ichnofauna whereCaririchium is also abundantly represented. Ingeneral however, many of the Chinese ichnofaunasare not ornithopod dominated, even though numeri-cally ornithopod trackways represent a small or inter-mediate component in many. As cited elsewhere inthis volume Lucas (2007: 22) suggested that ‘Creta-ceous tetrapod footprints can be distinguished fromJurassic tracks primarily by the abundance and nearubiquity of large ornithopod tracks’. This statementdeserves analysis, because while it is true thatlarge ornithopod tracks are relatively ubiquitous, not‘near ubiquitous’, they are only abundant in certainregions and deposits, including the Wealden andDakota Groups (Fig. 3). Lockley et al. (2012a) havealready suggested that East Asian ichnofaunas aresignificantly different in composition, being domi-nated in many regions by an abundance of smallnon-avian theropod (grallatorid) tracks (Grallators.l. and Asianopodus), and avian theropod (bird)tracks as well as forms like Minisauripus andvarious dromaeosaurid tracks (Velociraptorichnus,Dromaeopodus and Dromaeosauripus) which areapparently rare or absent in all other regions. In thisregard it is interesting to note that the South Ameri-can ichnofaunas are also heavily theropod-dominated,as are the Spanish ichnofaunas, and in both theseexamples these conclusions are based on substantialdata sets.
Although vertebrate ichnology has progressedrapidly in recent decades, there have been relativelyfew efforts to synthesize the large volume of datanow available. We have cited the Chinese data set(Table 1) as an example of a comprehensive compila-tion of tracksites, comparable to the South Americandata set provided by Leonardi (1994). However,we stress that other comprehensive data sets suchas those provided by Lockley et al. (2006b) for theJindong Formation of Korea, by Lockley et al. (2010a)for the Dakota Group of the western USA and byMoratalla & Hernán (2010) for the Cameros Basin ofSpain are regional in scope, and refer to discrete
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stratigraphic units. However, in these cases as wellas counting tracksites, the number of individualtrackways have been recorded allowing a quantitativeassessment of the proportion of different track types,rather than simple presence/absence data. Ultimatelysuch relative abundance data is necessary in order tobetter characterize the ichnofaunas and their faciesrelationships.
As an example of this potential to show quantita-tive trends we cite the evidence for an increase in theproportion of ornithopods between the basal EarlyCretaceous (Berriasian) and the later Early Creta-ceous (Aptian-Albian). This trend was recorded inde-pendently in Spain (Moratalla & Hernán, 2010) andnortheastern China (Matsukawa et al., 2014). Thistrend can also be inferred in Korea (Table 2, Fig. 2)where the abundance of ornithopods in the JindongFormation is far greater than in any of the underlying(older) units. Likewise the trend is evident in Canada(McCrea et al., 2014) where track-rich formationsfrom both intervals are available for study, and wheretrack-rich formations from both intervals are avail-able for study and where Currie (1995) has statedthat ornithopod tracks are very abundant (dominant)in the Aptian Gething Formation. As hinted above,the increase in abundance of large ornithopods mayalso correlate with an increase in average size duringthe Early Cretaceous.
Such differences in the types of data available forwidely different regions make for very generalizedsyntheses. Here we claim only to provide an overviewof track-bearing Lower Cretaceous deposits fromwhich relatively abundant data is available (Fig. 3). Itis beyond the scope of the present study to extractdata in a standardized format for all regions dis-cussed; indeed it is doubtful that anything more thanpresence/absence data can be extracted from some ofthe primary literature (see appendix in Lockley et al.,2012a). These obstacles to a standardized approachare compounded by the lack of consistency inichnotaxonomic practice. However, ichnologists areaware of this problem and have attempted to addressthe problem of ‘over-splitting’, especially in the caseof Chinese ichnotaxonomy (Lockley et al., 2013).In short it is necessary to have a consistentichnotaxonomy before making meaningful compara-tive analyses. Elsewhere in this volume for example,the ichnotaxonomy of large ornithopod tracks isreviewed (Lockley et al., 2014), with a view to high-lighting both obvious and subtle differences, andmoving towards a manageable ichnotaxonomy that isuseful in practice. For example, while acknowledgingthat there are subtle differences of opinion regardingthe similarities and differences between Amblydac-tylus and Caririchnium (the latter ichnogenus beingrepresented by four different ichnospecies on three
continents) there seems to be little dispute over thefact that both ichnogenera represent large faculta-tively bipedal ornithopods, that are abundantly rep-resented in the post-Neocomian Early Cretaceous(Aptian–Albian). In contrast Iguanodontipus is moretypical of the basal Cretaceous.
Finally it is important to note that while EarlyCretaceous ichnofaunas are quite distinct fromthose for other epochs, causing Lucas (2007) to rec-ognize a distinct Lower Cretaceous biochron, manyichnofaunas are facies-controlled, or facies-related.The best example among the ichnofaunas cited herewould be the differentiation between the Texas(Pittman, 1989) and southern European ichnofaunasassociated with carbonate platform facies (DallaVecchia, 2008; Sacchi et al., 2009) and all others asso-ciated with diverse clastic facies. Lockley, Hunt &Meyer (1994a) suggested that such differences areevidence of distinctive vertebrate ichnofacies, lateralso referred to as tetrapod ichnofacies (Hunt &Lucas, 2007; Lockley, 2007). Ichnofacies may be con-trolled by regional and global scale environmentalfactors such as latitude, climate and depositionalenvironment (Lockley, Hunt & Meyer, 1994b). Inshort, ichnofacies, like sedimentary facies, are vari-able and may intergrade in complex ways. All thesefactors, as well as age, and the dynamics of evolu-tionary turnover, influence the composition and dis-tribution of ichnofaunas on a global scale. In manyregions tracks are extremely abundant, and thecompilation of data sets is potentially very useful,especially when the age of the ichnofaunas,their ichnotaxonomy and facies relations are wellunderstood and provide well documented context.As stressed here, uncertainties about the age,ichnotaxonomy and other factors may compromise theutility of data and comparative analyses, at least inthe short term. However, as we hope to have shown,in the long term, databases are growing steadily involume and quality, as is their potential utility forichnofaunal analysis.
ACKNOWLEDGEMENTS
We thank Gareth Dyke for his efforts to organize theJehol-Wealden International Conference, held atSouthampton University, England, in September2013. Support to attend this conference was providedto the senior author (MGL) by the offices of theDinosaur Trackers Research Group (University ofColorado Denver). We also thank Richard McCreafor providing access to in press information onthe Canadian ichnofaunas. We thank Stuart Pond,University of Southampton and Matteo Belvedere,University of Padova for their helpful reviews.
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