From the Cretaceous of Thailand: Implications for Theropod Track Diversity Martin Lockley A,*, Masaki Matsukawa B, Yoshio Sato C, Malai Polahan C, Veerote Daorerk C

Cretaceous Research 27 (2006) 139e145 A distinctive new theropod dinosaur track

www.elsevier.com/locate/CretRes from the Cretaceous of Thailand: Implications for theropod track diversity Martin Lockley a,*, Masaki Matsukawa b, Yoshio Sato c, Malai Polahan c, Veerote Daorerk c

a Department of Geology, University of Colorado at Denver, P .O. Box 173364, Denver, Colorado 80217-3364, USA b Department of Earth Science E ducation, Tokyo Gakugei University, K oganei-Shi, Tokyo 184, J apan c Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Received 10 August 2002; accepted in revised form 20 October 2005 Available online 7 February 2006

Abstract

Highly distinctive, well-preserved, three-toed dinosaur footprints with bilobed heel impressions from the Cretaceous of Thailand are assigned to the new ichnotaxon Siamopodus khaoyaiensis. The tracks, which r epresent small- to medium-sized gracile theropods, are unlike any previ- ously k nown from Thailand or elsewhere. By contrast other robust, small- to medium-sized theropod tracks with bulbous heel impressions are reported from a new locality and shown to be similar to Lower Cretaceous tracks from elsewhere in Asia. When added to p reviously reported robust, large theropod tracks, the Cretaceous track record in Thailand appears dominated by a significant diversity of theropod track types that differ from one locality to the next. Thus, the track record is in general agreement with the skeletal record of theropods in Thailand. The occurrence of footprints with bilobed heel impressions is reviewed briefly. ? 2005 Elsevier Ltd. All r ights r eserved.

Keywords: Dinosaur tracks; Theropods; Cretaceous; Thailand

1. Introduction

A distinctive assemblage of tridactyl dinosaur tracks from the Mae Nam Sai Yai r iver valley in Khao Yai National Park, Thailand (Fig. 1), was reported b y Polahan and Daor- erk (1993). The track assemblage consists of 11 footprints preserved as natural casts on a loose b lock of medium grained sandstone preserving current ripple marks (Figs. 2 and 3). The locality is very inaccessible, requiring a hike of about 20 km southward from the National Park station over the Yai valley. Polahan and Daorerk (1993) observed that it is hard to ##state exactly$$ to which formation the footprint-bearing block belongs. They suggested it

* Corresponding author. E-mail address: [email protected] (M. L ockley).

0195-6671/$ -s ee front matter ? 2005 Elsevier Ltd. All r ights reserved. doi: 10.1016/j.cretres.2005.10.002

##probably$$ originated from either the Sao Khua or the Phu Phan formations. The ages of dinosaur bearing formations in Thailand are very hard to determine owing to lack of continuous outcrop, well-exposed sections, and diag- nostic index fossils. In their original description, Polahan and Daorerk (1993, fig. 4) provided a sketch of the slab and assigned numbers (1e1 1) to each of the tracks, beginning with the largest (1), which we designate as the holotype, h erein designated Chula- longkorn University Geological Museum (CUGM) specimen number F0020. We have redrawn the slab from the CUGM replica based on an accurate full-scale tracing (Fig. 3). W e have also designated each track a separate specimen number (see Table 1 and Section 4). Also, in order to simplify identi- fication and illustration of left and r ight tracks, we have reversed the tracing to produce a line drawing in positive rather than negative aspect: compare Figs. 2 and 3.

140 M. Lockley et al. / Cretaceous Research 2 7 (2006) 139e145 northeast of Bangkok.

2. Systematic ichnology

Dinosauria Theropod

Siamopodus ichnogen. nov. (Figs. 2e5)

Derivation of name. Track from ancient Thailand (or ##Siam$$).

Type material. Chulalongkorn University Geological Museum (CUGM) specimen numbers CUGM F0020eF0030 are used for 11 complete or partial track casts (topotypes) on a fiberglass replica of entire surface (Figs. 2 and 3). A partial replica of the surface in University of Colorado at Denver collection is designated CU 214.46. korn University Geological Museum (CUGM) collections (specimen numbers F0020eF0030 cover all 11 tracks). Compare with Fig. 3 for detail and scale.

Holotype. Track number CUGM F0020, the largest specimen (Figs. 2e5), also designated as CU 214.46 in the Univer- sity of Colorado at Denver collections. Paratypes. Includes topotypes CUGM F0021eF0030. Numbers 2, 3, 5, 6, and 8e10 (sensu Polahan and Daorerk, 1993, fig. 4) correspond to F0021, F0023, F0026, F0029, F0028, F0024 and F0025 r espectively (see Table 1). Numbers 7 (F0030) and 11 (F0022) are indeterminate.

Horizon and locality. Kohrat Group, Mae Nam Sai Yai river, Khao Yai National Park, Thailand (see Fig. 1).

Diagnosis. Small- to medium-sized tridactyl theropod track with slender toes and sub-symmetric bilobed heel. Inner hypex between digits II and III situated posterior to outer hypex between digits III and IV.

Description. Tridactyl, slender toed track with p halangeal formula of 2-3-4? Corresponding to digits II, III, and IV. About 83e93% as wide as long; length range 14e30 cm width range 11e25 cm (see Table 1). Hypex between digits II and III situated p osterior to hypex between digits III and IV.

M. Lockley et al. / Cretaceous Research 2 7 (2006) 139e145 141 row denotes flow direction indicated b y current ripples. Numbers 1e11 after Polahan and Daorerk (1993). Note: slab is reversed, relative to natural cast, in order to show original aspect of tracks. 1¼ F0020). BeD, p aratypes (tracks 6, 10 and 3 respectively); small b lack ar- rows d0e02no0t)e. BaentDeri,op ra position otraf hypex 1b 0e tawnede n3 digits tIivIIe alny)d; sIVm.

Heel sub-symmetrical, bilobed and about one third of track width (range 34.2e37.6%; mean 36.1, N ¼ 3). dPthac( er anngde 3st4r.id2ee pattern munecaenrt3 a6in.1. PN os¼ sib3 l)e. heel trace of large track maker on edge of b lock 112 cm anterior to heel trace of track 1 suggests single step length. Tracks 2, 3 and 4 may form sequence with steps of 44 (2e3) and 45 cm (3e4) and stride of 73 cm (pace angulation 135 ?). Tracks 10 and 7 may form a step of about 51 cm.

3. Systematic discussion

No small- or medium-sized tridactyl tracks of theropod af- finity are k nown with a distinctive bilobed heel (Figs. 4 and 5) with the possible exception of Atreipus from the Late Triassic of North America and Europe (Fig. 6B). Atreipus typically has an associated manus and though interpreted b y some as Fig. 4. Photographs of Siamopudus khaoyaiensis A, holotype, track 1 (¼F0020). B, p aratype, track 6 (¼F0029, orientated up) and paratype, track 8 (¼F0028, oFirige.n4 t.ateP dh down). C, p aratype, utrdaucsk 1h0a (¼F0025). Holotype ,alt sroa p reserved as 0C).UB 2,1p 4a.4ra6t.y

142 M. Lockley et al. / Cretaceous Research 2 7 (2006) 139e145

Fig. 6. Tracks with bilobed heels. A, Siamopodus holotype. B, the late Triassic archosaurA treipus. C, the mid-Cretaceous ornithopod Caririchnium. D, a modern wolf. Scale bar represents 15 cm. theropodan (Thulborn, 1990), it is generally considered to be the track of an ornithischian (ornithopod), or even a non-dino- saurian archosaur (Olsen and Baird, 1986). The only other dinosaur tracks that often have a bilobed heel are those of large Cretaceous ornithopods (iguanodontids and hadrosaurs, Fig. 6C) from North America (Currie et al., 1990, 2003; Lockley and Hunt, 1995; Lockley et al., 2004). These forms however have bulbons, well-padded digits and tracks that are as wide as long. Such bilobed heel morphology is somewhat reminiscent of that of modern cats and dogs (Fig. 6D), but is rare in most other vertebrates. Siamopodus khaopaiensis is therefore unique. The repeti- tion of this distinctive morphology at b oth ends of the size range within the sample (especially tracks 1, 6 and 10) indi- cates that it is a consistent morphological feature. Possible size-related changes include a slight increase in digit

Table 1 Morphometric p arameters for Siamopodus khaoyaiensis divarication as size increases. If tracks in the sequence 2-3-4 are part of a trackway, then the wide trackway (¼low pace angulation) fisa ut nraucskuwala, as hise ntht eh eevw iiddeen ttr aocuktwwaaryd ( r ¼oltoatwiop na cofe tahne- axis of the p es. These features however may b e subject to lo- comotor variation in response to substrate conditions. The posterior location of the hypex between digits IIand III relative to the more anterior hypex between III and IV is also consistent between small and large tracks. Treated as a ratio of foot length the mean values are 26.2 and 34.2 r espectively (see Table 1).

4. Discussion

Dinosaur tracks have been known from Thailand since 1985. Fifteen medium-sized theropod tracks were reported from the Khorat Group in the Phu Luang Wildlife Sanctuary, province of Loei (Buffetaut et al., 1985, 1997; Buffetaut and Ingavat, 1985). These are probably from the Cretaceous Phu Phan Formation (Suteethorn et al., 1995; Buffetaut and Sutee- thorn, 1998a,b). Since 1985, four other track sites have b een reported, including the Khao Yai site reported by Polahan and Daorerk (1993) and r e-described herein. Other significant dinosaur tracks discoveries from Thailand include an assemblage con- taining small tracks of quadrupedal ornithischians (probably ornithopods) from the Phra W ihan Formation at Hin Lat Pra Chad, north-northwest of Khon Kaen (Buffetaut and Sutee- thorn, 1993; LeLoeuff et al., 2002; Fig. 7B herein; Matsukawa et al., 2006) and large theropod tracks, also from the Phra Wi- han Formation, at Phu Faek, near Kalasin (Buffetaut et al., 1997). According to LeLoeuff et al. (2002), this locality also yields sauropod tracks. We have been unable to confirm this interpretation, and so h ave not included sauropod tracks in our synthesis (Table 2). However, we acknowledge that sauropod tracks are k nown from the region, b oth in Laos (Allain et al., 1997; Matsukawa et al., 2006) and southern China (Lockley et al., 2002). The Hin Lat Pra Chad discovery is particularly significant for two reasons: first, the Phra W ihan Formation in this r egion

Track Left/Right Length Width Divarication Hypex-heel (H-h) (%) Hypex-heel/pes (H-h/FL) (%) number IIeIIIIIIeIV

1 R 30 25 36? 36? 9.0 (30) 12.2 (40.7) 2 L 14 e37? e3.2 (21.5) 4.2 (28.2) 3 R

14.9 13.5 21? 33? 4 L 13.5 5 (L) (12) 6 R 14 11.5 33? 32? 4.2 (30.0) 5.0 (36.7) 8 (R) 17 16.5 9 10 R 15.5 12 27? 28? 3.6 (23.2) 4.8 (31.0) Mean 16.99 15.70 30.80? 32.25? Mean % eeee(26.2) (34.2)

For h istorical continuity, numbers 1e10 follow Polahan and Daorerk (1993, fig. 4). Equivalent specimen numbers are given in the systematic section. Compare with Fig. 3. Hypex-heel length, and Hypex-heel/pes length (FL) as %, given in right column.

M. Lockley et al. / Cretaceous Research 2 7 (2006) 139e145 143 has b een dated as Neocomian (Berriasian-Barremian) on the basis of p alynomorphs (Racey et al., 1994, 1996; Buffetaut et al., 1997; LeLoeuff et al., 2002), and second, this was the first discovery of tracks of such small quadrupedal ornithischians in the Cretaceous (Matsukawa et al., 2006). Similar tracks have recently been found in the Cretaceous of Canada (Richard McCrea and Martin Lockley, unpublished data), and it is possible that this same type also occurs in Zimbabwe (Lingham-Soliar and Broderick, 2000), where the age of the track-bearing b eds is uncertain (Richard McCrea and Martin Lockley, unpublished data). A fifth site, has recently b een discovered (in 2001) in the Cretaceous of the Lao Nat region, in the Mekong River valley northwest of Nakhon Phanom, but has yet to b e studied in detail. However, the tracks, which are quite abundant, but evi- dently all of the same type (Fig. 8), are attributable to theropods, and are probably Cretaceous in age, from the Khorat Group. They are similar to tracks from the Lower Cre- taceous of Inner Mongolia, especially with respect to the bulbous heel pad (Lockley et al., 2002). Similar tracks, with enlarged h eel impressions, have also b een found in the Lower Cretaceous of J apan (Fig. 8), and recently named A sianopodus pulvinicalx (Matsukawa et al., 2005). Following Buffetaut and Suteethorn (1998a,b) the present state of k nowledge regarding the stratigraphic distribution of dinosaur track sites in Thai- land can be updated as shown in Table 2. Although our knowledge of dinosaur tracks from Thailand is still in a preliminary state, it has advanced considerably in re- cent years. Fortunately most of the tracks so far reported are generally well p reserved. This applies especially to the tracks from Khao Yai and the newly discovered tracks from Lao Nat. The dominance oftheropod tracks found at all sites is note- worthy. Given that ichnofaunas in many regions comprise only one or two identifiable ichnotaxa, which often occur repeatedly at multiple sites, the Thailand theropod fauna/ichnofauna suggests significant diversity and geographical variability during the Early Cretaceous. As shown in Fig. 7A, C and D, well- preserved tracks from three different localities (Phu Faek, Lao Nat, and Khao Yai respectively) indicate three quite distinct ichnotaxa, of which only Siamopodus has so far been named. Theropod tracks from Phu Luang and tridactyl tracks from Hin Lat Pra Chad are less well-preserved and distinctive, but may also belong to different theropod ichnotaxa. Thus, there could be at least one legitimate theropod ichnotaxon for each of the five k nown Thailand track localities. This is in

Table 2 Inferred age and stratigraphic r elationships of dinosaur track sites from Thailand Site name Formation Age Track type Phu Luang Phu P han ?Barremian Theropod tracks Sanctuary Formation Khao Yai Sao Khua or ? Neocomian Siamopodus theropod Phu Phan Hin Lat Pra Chad Phra W ihan ?Berriasian Theropod-ornithopod Phu Faek Phra W ihan ?Berriasian Theropod Lao Nat Khorat Group Cretaceous Asianopodus theropod tracks from the Cretaceous of Thailand (and China). All drawn to same scale. A, large theropod trackway from Phu Faek. B, ornithopod tracks from Hin Lat Pra Chad. C, theropod trackway from Lao Nat. E, theropod tracks from the Lower Cretaceous of Inner Mongolia, China (compare with Fig. 8). addition to at least three other distinctive track types from Hin Lat Pra Chad including the aforementioned ornithischian footprints (Matsukawa et al., 2006, and Fig. 7B herein). Such distributions are consistent with results from studies of Cretaceous tracks in China (e.g., Lockley et al., 2002). Here again we find a preponderance of theropod tracks, some- times with sauropod and b ird tracks in red beds associated with r elatively small continental basins. The presence of sauropod tracks in the Cretaceous of L aos (Allain et al., 1997; Matsukawa et al, 2006) suggests a similar, saurischian dominated assemblage for the Laos and Thailand region. However, we are not convinced that unequivocal examples of sauropod tracks are yet known from Thailand (contra LeLoeuff et al., 2002). Tracks of ornithischian (ornithopod) dinosaurs are largely absent from most of China and occur only sporadically in the north (Li et al., 2002; Zhang et al., 2006), as one approaches Cretaceous temperate latitudes, and to the east, nearer Cretaceous coastal regions, i.e., in present day Liaoning and Jilin, China; Korea; and Japan (Lim et al., 1994;

144 M. Lockley et al. / Cretaceous Research 2 7 (2006) 139e145 insimilar to Lower Cretaceous tracks from Inner Mongolia (B) and Japan (C). N ote bulbous heel associated with many tracks. Specimen numbers refer to replicas the CU Denver collection.

Matsukawa et al., 1995, 2006). The theropod-rich track assemblages of Thailand confirm this general picture of saurischian dominated ichnofaunas in low-latitude red bed facies of southeastern Asia. Such assemblages indicate the potential for improved understanding of theropod morphology and diversity where distinctive, well-preserved material is available (Fig. 7). A number of distinctive theropod dinosaurs are known from the Cretaceous of Thailand including Siamotyrannus (Buffe- taut et al., 1996); a possible spinosaurid, S iamosaurus (Buffetaut and Ingavat, 1986); an ornithomimosaur (Buffetaut and Suteethorn, 1998b, 1999); and a possible compsognathid (Buffetaut and Ingavat, 1984). Thus, although feet of these taxa are not known, the b ody fossil record suggests four different theropods that express a r ange of morphology from small and gracile to large and robust. Thus, in general terms there is agreement between the theropod b ody fossil r ecord of four disparate and distinct taxa and the track record of three quite distinct theropod ichnotaxa, from three sites, and additional two sites with other theropod and/or tridactyl tracks.

Acknowledgments

This study was made possible b y a grant in aid for Uni- versity and Society Collaboration of the Japanese Ministry of Education, Science Sports and Culture (Matsukawa, no 1183303, 199902001). W e thank Varavudh Suteethorn, Geo- logical Survey Division, Thailand for facilitating access to

M. Lockley et al. / Cretaceous Research 2 7 (2006) 139e145 145 specimens for comparative study. We also thank Eric Buffe- taut, CNRS, Paris and Jean Le Loeuff, Mus´ ee des Dino- saures, Esp´ eraza, France for general discussion and Richard McCrea for helping with access to specimens from the Cre- taceous of Canada.

References

Allain, R., Taquet, P., Battail, B., Dejax, J., Richir, P., Veran, M., Sayarath, P., Khenthavong, B., Thamvirith, P., Hom, B., 1997. Pistes de dinosaures dans les niveaux du Cre´ tac´ e Inf´ erieur de Muong Phalane, province de Savanna- khey (Laos). Comptes Rendus de l# Acad émie des Sciences, Paris 325, 815e821. Buffetaut, E., Ingavat, R., 1984. A very small theropod from the upper Jurassic of northeastern Thailand. Comptes Rendus de l# Acad émie des Sciences, Paris 298, 915e918. Buffetaut, E., Ingavat, R., 1985. The Mesozoic vertebrates of Thailand. Scien- tific American 253, 80e89. Buffetaut, E., Ingavat, R., 1986. Unusual theropod teeth from the Upper Juras- sic of Phu W iang, northeastern Thailand. Revue de Paleobiologie 5, 217e220. Buffetaut, E., Suteethorn, V., 1993. The dinosaurs of Thailand. Journal of Southeast Asian Earth Sciences 8, 77e82. Buffetaut, E., Suteethorn, V., 1998a. The b iogeographical significance of the Mesozoic vertebrates from Thailand. In: Hall, R., Holloway, J.D. (Eds.), Biogeography and Geological Evolution of SE Asia. Blackhuys, Leiden, Netherlands, pp. 83e90. Buffetaut, E., Suteethorn, V., 1998b. Early Cretaceous dinosaurs from Thai- land and their bearing on the early evolution and b iogeographical history of some groups of Cretaceous dinosaurs. In: Lucas, S.G., Kirkland, J., Estep, J.W. (Eds.), Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14, 205e210. Buffetaut, E., Suteethorn, V., 1999. The dinosaur fauna of the Sao Khua For- mation of Thailand and the b eginning of the Cretaceous radiation of dinosaurs in Asia. Palaeogeography, Palaeoclimatology Palaeoecology 150, 13e23. Buffetaut, E., Ingavat, R., Sattayarak, N., Suteethorn, V., 1985. First dinosaur footprints from southeast Asia: Carnosaur tracks from the lower Creta- ceous of Thailand. Comptes Rendus de l# Acad émie des Sciences, Paris 301, 643e648. Buffetaut, E., Suteethorn, V., Tong, H., 1996. The earliest k nown tyrannosaur from the Lower Cretaceous of Thailand. Nature 381, 689e691. Buffetaut, E., Suteethorn, V., Tong, H., Chaimanee, Y., Khansubha, S., 1997. New dinosaur discoveries in the Jurassic and Cretaceous of northeastern Thailand. In: The International Conference on Stratigraphy and Tectonic Evolution of Southeast Asia and the South Pacific. 19e24th August, Bang- kok, Thailand, pp. 177e187. Currie, P.J., Nadon, G., Lockley, M.G., 1990. Dinosaur footprints with skin impressions from the Cretaceous of Alberta and Colorado. Canadian Journal of Earth Sciences 28, 102e1 15. Currie, P.J., Badamgarav, D., Koppelhus, E.B., 2003. The first late Cretaceous footprints from the Nemegt Locality in the Gobi of Mongolia. Ichnos 10, 1e13. LeLoeuff, J., Khansubha, S., Buffetaut, E., Sutethorn, V., Tong, H., Souillat, C., 2002. Dinosaur footprints from the Phra W ihan Formation (Early Cretaceous of Thailand). Comptes Rendus Paleovol 1, 287e292. Li, D., Zhang, J., Li, M., Lockley, M.G., Bai, Z., 2002. Diverse dinosaure pterosaurebird ichnofaunas from the Cretaceous of Gansu Province, China. Journal of Vertebrate Paleontology 22 (Supplement to No. 3), 79. Lim, S.K., Lockley, M.G., Yang, S-Y., Fleming, R.F., Houck, K.A., 1994. Pre- liminary r eport on sauropod tracksites from the Cretaceous of Korea. Gaia: Revista de Geociencias, Museu Nacional de Historia Natural, Lisbon, Por- tugal 10, 109e1 17. Lingham-Soliar, T., Broderick, T., 2000. An enigmatic Early Mesozoic dinosaur trackway from Zimbabwe. Ichnos 7, 135e148. Lockley, M.G., Hunt, A.P., 1995. Dinosaur Tracks and Other Fossil Footprints of the Western United States. Columbia University Press, New York, 338 pp. Lockley, M.G., Wright, J.L., White, D., Matsukawa, M., Li, J., Lu, F.L., Hong, L.M., 2002. The first sauropod trackways from China. Cretaceous Research 23, 363e381. Lockley, M .G., Nadon, G., Currie, P.J., 2004. A diverse dinosaurebird footprint assemblage from the Lance Formation, Upper Cretaceous, eastern Wyoming: implications for ichnotaxonomy. Ichnos 11, 229e249. Matsukawa, M., Futakami, M., Lockley, M.G., Chen, P., Chen, J., Cao, Z., Bolotsky, U.L., 1995. Dinosaur footprints from the Lower Cretaceous of eastern Manchuria, northeastern China: implications for the r ecognition of an ornithopod ichnofacies in East Asia. Palaios 10, 3e15. Matsukawa, M., Shibata, K., Kukihara, R., Koarai, K., Lockley, M.G., 2005. Review of Japanese dinosaur track localities: Implications for ichnotaxonomy, p aleogeography and stratigraphic correlation. Ichnos 12, 201e222. Matsukawa, M., Lockley, M.G., Li, J., 2006. Cretaceous terrestrial b iotas of East Asia, with special reference to dinosaur-dominated ichnofaunas: towards a synthesis. Cretaceous Research 27 (1), 3e21. Olsen, P., Baird, D., 1986. The ichnogenus Atreipus and its significance for Triassic biostratigraphy. In: Padian, K. (Ed.), The Beginning of the Age of Dinosaurs. Cambridge University Press, Cambridge, pp. 61e87. Polahan, M., Daorerk, V., 1993. Report on additional discovery of dinosaur#s footprints in Thailand. In: International Symposium on Biostratigraphy of Mainland Southeast Asia: Facies and Paleontology. January 31steFebru- ary 5th Chiang Mai, Thailand, pp. 225e230. Racey, A., Goodall, J.G.S., Love, M.A., Polachan, S., Jones, P.D., 1994. New age of the Khorat Group of northeast Thailand. In: Anguswathana, P.T., Wongwanich, W., Tansathien, S., Wongsomsak, S., Tulyatid, J. (Eds.), Pro- ceedings of International Stratigraphic Correlation of Southeast Asia, pp. 245e256. Racey, A., Love, M.A., Canham, A.C., Goodall, J.G.S., Polachan, S., Jones, P.D., 1996. Stratigraphy and r eservoir potential of the Mesozoic Khorat Group of NE Thailand. 1. Stratigraphy and sedimentary evolution. Journal of Petroleum Geology 19, 5e40. Suteethorn, V., Buffetaut, E., Martin, V., Chaimanee, Y., Tong, H., Triamwichanon, S., 1995. Thai dinosaurs, and updated review. In: Sixth Symposium on Mesozoic Terrestrial E cosystems and Biota. China Ocean Press, Beijing, pp. 133e136. Thulborn, R.A., 1990. Dinosaur Tracks. Chapman and Hall, London, 410 pp. Zhang, J., Li, D., Li, M., Lockley, M.G., Bai, Z., 2006. Diverse dinosaur-, pterosaur-, and b ird-track assemblages from the Hakou Formation, Lower Cretaceous of Gansu Province, northwest China. Cretaceous Research 27 (1), 44e55.