Dinosaur tracksites from the Cretaceous Sagok Formation in the Uiseong Regional Geopark, South Korea: historical, palaeobiological perspectives

ABSTRACT The relatively large (1,600 m2) Jeo-ri dinosaur tracksite from the Lower Cretaceous Sagok Formation in the Uiseong County area in Gyeongsangbuk-do (North Gyeongsang Province) was the first dinosaur tracksite designated as a Korean Natural Monument (Number 373). However, it has never been described in any detail. It is shown to reveal more than 380 footprints attributed to theropods, sauropods and ornithopods. The trackways show a preferred orientation to the north and northwest with some similarly sized ornithopod trackways suggesting gregarious behaviour. A smaller tracksite from the Mancheon-ri site, representing the Sagok Formation also reveals theropod, sauropod and ornithopod trackways. These include trackways of two small ornithopods (footprint lengths ~9.9-11.5 cm) that indicate deceleration while transitioning from bipedal to quadrupedal progression. One trackway shows rare evidence of pausing to ‘stand’ and leave ‘side-by-side’ footprints. The Sagok Formation is considered correlative with the Haman Formation which is well known for its dinosaur tracksites in Gyeongsangnam-do (South Gyeongsang Province). This correlation underscores the importance of understanding the remarkable abundance and spatiotemporal distribution of dinosaur tracks in the Lower Cretaceous of Korea.


Introduction
In recent years dinosaur tracks have been reported from multiple Cretaceous localities in South Korea (Kim et al. 2012a;Lockley et al. 2012 and references therein). The most intensively studied regions include, in order of ascending geological age, sites from in and around Goseong County (Goseong-gun) in Gyeongsangnam-do (South Gyeongsang Province) notably from the Jinju Formation in the Jinju City area, and in the Haman and Jindong formations of Haman, Namhae and Goseong counties (Kim et al. 2019a(Kim et al. , 2019b(Kim et al. , 2019c(Kim et al. , 2020(Kim et al. , 2021bLockley et al. 2022 and references therein). These areas are of sufficient importance to have yielded ichnological sites designated as Natural Monuments (NM): e.g., NM 534 and NM 566, in the Jinju Formation, NM 222, the Koreanaornis type locality, NM 499, NM 474, and NM 395 in the Haman Formation, and NM 411, the Goseong Deongmyeong-ri (Deokmyeong-ri) tracksite area in the Jindong Formation. Research into the tetrapod ichnology of these Natural Monuments and other nearby sites has attempted to describe the ichnofaunas in detail. As a result, the rate of publication on such nationally and internationally recognised sites has generally been brisk.
Despite the undeniable interest in Cretaceous tetrapod ichnology in Korea it has not always been possible for detailed documentation to keep up with the pace of tracksite discovery. Thus, a significant number of known sites lack detailed documentation in the scientific literature. The purpose of this report is therefore to described two significant sites from the Cretaceous Sagok Formation of Uiseong County in Gyeongsangbuk-do (North Gyeongsang Province) ( Figure 1) neither of which was previously described in detail. The larger of these two sites, the Jeo-ri site, discovered in 1987, is of historical importance and has the distinction of having been designated as Natural Monument 373 in 1994. It was also the first Korean dinosaur tracksite to be so designated and it was also the first to be covered with a large roof structure, erected after 1998 ( Figure 2). The smaller of the two sites, the Mancheon-ri site, also in the Sagok Formation is only about 700 m geographically NNW of the Jeo-ri site. Both are situated on the NW side of the Gumseongsan Caldera, and both represent sites within the area recently designated as the Uiseong Regional Geopark . In the following sections we describe the dinosaur ichnofaunas from the Jeo-ri and Mancheon-ri sites in detail.

Historical background
The first reported dinosaur tracksite from Uiseong Country, known as the Jeo-ri tracksite was exposed by a landslide after road construction in the summer of 1989. Subsequent survey by Kim and Seo (1992) reported the recognition of a total of 25 dinosaur trackways, representing 316 individual tracks. Kim and Seo (1992) mentioned four ichnotaxa such as Koseongosauripus onychion, Megalosauropus sp., Ultrasauripus ungulatus, and Elephantosauripus metarcapus in the report submitted to the Office of Cultural Properties (Cultural Heritage Administration). These ichnotaxa were regarded as nomina dubia due to uncertainty of their validity and incomplete descriptions (Lockley et al. 1994;Kim and Huh 2018). The track-bearing deposits of the Jeo-ri tracksite are interpreted as sheetflood deposits on a floodplain under a seasonal palaeoclimatic condition with alternating of wetting and drying periods (Paik et al. 2013).
The Mancheon-ri tracksite was first reported to reveal ~50 dinosaur tracks including two small (baby) dinosaur trackways (Kim 2005). Although he didn't unambiguously identify these tracks, his statement indicates the characteristics of Caririchnium. However, Lim et al. (2008) interpreted the tracks as baby sauropod tracks based on rounded shape of the tracks. In renewed research at the tracksite in 2021, it was confirmed that the small dinosaur trackways are Caririchnium trackways showing both bipedal and quadrupedal locomotion in each trackway (Kim et al. 2021a).

Geologic setting
During the Cretaceous, more than 10 km thick non-marine successions of the Sindong, Hayang, and Yucheon groups formed in the Gyeongsang Basin, south-east Korea (Chough and Sohn 2010). The Gyeongsang Basin consists of three subbasins, Milyang (Chang 1977) or Jinju (Chough and Sohn 2010), Uiseong, and Yeongyang subbasins from south to north, and the group-level lithostratigraphic units can be correlated between these subbasins. These successions were deposited between the Hauterivian to Barremian based on microfossils (Choi 1985(Choi , 1987Choi and Park 1987) or during the Aptian based on the detrital zircons (<118 Ma; Lee et al. 2010).
The Sagok Formation, focus of this study, occurs in the middle Hayang Group of the Uiseong subbasin. The formation mainly consists of purple mudstone and siltstone with occasional greenish grey sandstone, and is underlain by the purple mudstone and  siltstone of the Hupyeongdong Formation and overlain by a ~ 5 m thick Gusandong Tuff, which is a key bed for the lithostratigraphic correlation throughout the Hayang Group (Chough and Sohn 2010). Age-definitive fossils are not reported from the Sagok Formation. However, considering the occurrence of 99.8 Ma-old detrital zircon from the Sagok Formation (Choi and Kwon 2019) and the age of the Gusandong Tuff (ca. 97 Ma, Jwa et al. 2009,103-104 Ma, Kim et al. 2013, the depositional age of the Sagok Formation can be constrained as early Cenomanian. Although detailed sedimentological study has not yet been conducted in the study area, occurrence of sedimentary structures such as mudcracks, wave ripples, small invertebrate trace fossils, evaporite mineral casts as well as evidence of weak paedogenesis from the Sagok Formation, observed ~25 km east of the study area, suggests lake margin to shallow lake environments (Kim et al. 2019), of which many such features are also observed from our study area.

Methods and previous work
Methods of tracksite documentation have evolved considerably since the Jeo-ri tracksite was first very briefly mentioned in the Korean palaeontological literature (Kim and Seo 1992, p. 203, Pls. V-VI). As detailed in a recent report to Uiseong County (Kim et al. 2021a) preliminary maps were made of both sites between 1992 and 2008, and further analysis of the site was presented to the National Research Institute of Cultural Heritage by Paik et al. (2013). The first map of the Jeo-ri site (Kim and Seo 1992, p. 203) was very sketchy and imprecise, but it was accompanied by photographs of historical interest (Figure 3) taken at least two years before the site was designated as NM 373, and before the roof structure was erected. The first map of the Mancheon-ri site appeared in an unpublished master's thesis (Kim 2005) and was accompanied by crude outlines of sauropod and ornithopod tracks drawn from photographs.
The pre-2013 reports are mostly of interest with respect to how the resolution of tracksite maps, and the standard of tracksite monitoring compares with the mapping and accuracy of documentation at both the Jeo-ri and Mancheon-ri since 2021, after drone technology was employed (Kim et al. 2021a). For example Paik et al. (2013, p. 288) reported 'diverse footprints (over 300) in a small area' forming '12 sauropod trackways, 10 ornithopod trackways, and 1 theropod' (trackway total 23 trackways) and recommended that 'a brochure be published briefly explaining the tracksite . . . to educate the residents about the natural and social significance of the tracksite'. By contrast the most recent survey has recognised 19 sauropod, 14 ornithopod and 4 theropod trackways (Total 37 trackways). This represents a significant database increase from 23 to 37 (= +68%).
The 3D maps produced as the result of the present survey Kim et al. (2021a, figs. 50 and 51) for the Jeo-ri and Manchon-ri sites respectively, were obtained by first using a DJI Mavic Pro2 drone, DJI Phantom 4 pro drone, and Sony A7r III to obtain multiple images of the tracksite surfaces. The obtained photos were processed in order of photo alignment, point cloud data extraction, mesh data production, and texture production by SfM (Shift from Motion) technique using Photogrammetry software. Using a 3D model, a colour image and a shaded relief image were produced as an ortho image. For the orthographic projection image (ortho image), the slope representing the original dinosaur trackregistration surface, was converted into a projection reference plane for the production of a line drawing map.
By inspecting the tracksite surfaces on the ground it was possible to resolve the individual and isolated trackways and measure them. Photogrammetic images including colour depth, elevation, and other imaging options such as contouring, were obtained for selected trackway segments in the Mancheon-ri tracksite using Nikon D600 camera (16-80 mm lens), Agisoft PhotoScan Professional (v. 1.7.5 build 13,229), Meshlab, and Paraview (Romilio, 2020). The standard measurements obtained by Kim et al. (2021a) for all recognisable individual tracks and trackway parameters were as follows: length (L) and width (W) of pes, and manus, where available, step or pace length (PL), stride length (SL) and pace angle (PA): see supplemental information figures SI 1 and SI 2. Following the data organisation methods presented in the report of Kim et al. (2021a), the prefixes T, S and O were used for trackways of theropods, sauropods and ornithopods respectively, with trackways numbered (tw1, tw2, tw3 etc.) from left (SW) to right (NE) across outcrop. Left (L) and right (R) and manus (m) and pes (p) tracks are distinguished with numbers 1,2, 3 etc., used as suffixes to distinguish consecutive tracks from proximal to distal.  Thus, a typical series would be Stw1Rp1, Stw1Rm1 etc., (see Kim et al. 2021a, table 4). To avoid duplication of this database, we present only the mean values derived for track sizes (L and W), paces (PL,) stride (SL) and pace angle (PA) for each trackway (Tables 1 and 2).

Site and trackway descriptions
The Jeo-ri tracksite The Jeo-ri tracksite is by far the largest of the two sites described herein. As originally noted by Paik et al. (2013) the track-bearing surface is ~1,600 m 2 (Figures 3-5) and the track-bearing beds consist of interlaminated fine-grained sandstone to siltstone and mudstone. The exposed surface, a sandstone bed, is broken by multiple tension fractures with a NE strike that break up the surface (Figures 3 and 4). This gives the outcrop the appearance of having multiple track-bearing surfaces. Track preservation is variable and varies between 1.5 and 2.0 on the four-point (0-1-2-3) scale of Belvedere and Farlow (2016).

The Jeo-ri trackways
As detailed in Tables 1 and 2, there are 2 measurable theropod, 19 measurable sauropod and 14 measurable ornithopod trackways. The numbers of individual tracks representing each of these three groups are 18, 303 and 62 respectively (total 383): compare with the total of over 300 tracks reported by Paik et al. (2013). The two measurable theropod trackways have very similar lengths and widths (mean L and W 26.0 cm and 19.3 cm) respectively (mean L/W 1.35) but differ in step length: Ttw1 with 10 tracks and Ttw2 with three tracks have mean pace lengths of 100.6 cm and 157.5 cm respectively. This difference is reflected in a narrower trackway (higher pace angle, or reduced straddle) in trackway Ttw2 (Table 1). Track lengths of 25.0 cm are close to the arbitrary cut off length of 25.0 cm proposed by Thulborn (1990) to differentiate small from large theropod tracks. The total number of theropod tracks is ~18 allowing for five additional unmeasured tracks in trackways Ttw3 and Ttw4.
A total of 19 sauropod trackways, representing 303 individual tracks were recognised including trackways Stw8, Stw7 and Stw5 with 18, 17 and 16 consecutive tracks respectively ( Figure 5). All individual trackways were illustrated by outline drawings in Kim et al. (2021a). The former two trackways (Stw8, Stw7) are the largest trackways with mean pes track lengths of 79.8 cm and 83.5 cm and L/W ratios of 1.25 and 1.24 respectively. The smallest mean pes track length (32.5 cm) is seen in trackway Stw19 (Table 2). The trackways are mostly narrow gauge and only show pes claw traces registered sporadically in about half the trackways (Kim et al. 2021a). Sauropod trackway orientations are mainly concentrated in the northwest quadrant ( Figure 5).
A total of 14 ornithopod trackways, representing 62 individual tracks were recognised. All indicate bipedal progression. The tracks are on average as long as wide (mean L/W ratio of 1.01). The largest trackmaker had a footprint length of 35.5 cm and the smallest had a footprint length of 18.7 cm. Ornithopod trackway orientations are more strongly concentrated in the north to north northwest sectors than is the case for sauropod trackways and in eastern part of the outcrop side-by-side, near-parallel trackways (Otw9-Otw14) are noted ( Figure 5).

The Mancheon-ri tracksite
The Mancheon-ri tracksite is much smaller than the Jeo-ri tracksite, with an area of only ~10 x ~ 15 m (150 m 2 ). The visible tracks occur in several stratigraphic levels within less than a metre of vertical section of medium-grained sandstone with thin (mm-thick) siltmud partings (Kim et al. 2021a, fig. 9). The tracksite can be divided into areas where different surfaces are exposed ( Figure 6). These fall into two categories: 1) surfaces with clearly defined trackways and 2) areas with poorly preserved trackways that appear irregularly trampled. A total of ~115 tracks have been recognised (Kim et al. 2021a, fig 30: Figure 6 herein). The results of photogrammetic surveys of the site did not produce visually clear results due to the smaller trackways being too shallow to show well-defined relief: see Kim et al. (2021a) for examples.
Well-defined trackways include a single sauropod trackway (Stw1) comprised of four pes and two manus tracks oriented to the west, associated with the stratigraphically lowest (oldest) surface ( Figure 6, Table 3). The next stratigraphic level is the most interesting and reveals relatively clear evidence of three ornithopod trackways, a theropod trackway and some faint isolated tracks. The most visually obvious ornithopod trackway represents a large bipedal animal (mean footprint length 23.7 cm) with trackway (Otw3) oriented to the west. Tracks in this trackway are slightly longer than wide (L/W 1.08). The two smaller ornithopod trackways have mean lengths 11.5 and 9.9 cm for Otw1 and Otw2 respectively, with corresponding L/W ratios of 1.03 in both trackways. Corresponding manus lengths of 3.8 cm and 3.5 cm indicate animals progressing quadrupedally to the south, although manus tracks are not seen to be associated with all pes tracks. Theropod trackways Ttw1 and Ttw2 have mean track lengths of 21.3 and 15.6 cm respectively and are also oriented towards the south (Table 3).

Ichnofaunal assemblages: comparisons and contrasts
The ichnofaunal assemblages from both the Jeo-ri and Mancheon-ri sites have the same composition: i.e., they reveal recognisable theropod, sauropod and ornithopod trackways. The main difference is that the Jeo-ri site is sauropod dominated with 19 out of 35 measurable trackways (= ~54%). However, the upper levels of the Mancheon-ri tracksite reveal sauropod tracks that are not resolved into a known number of trackways. The Jeo-ri tracksite is associated with a single surface, whereas the Mancheon-ri tracksite is 'time averaged' representing track registration on different surfaces.
Superficially the Sagok Formation tetrapod tracks assemblage looks quite different from the time-equivalent Haman Formation ichnofaunas, with the Haman assemblages including a large number of smaller tracks attributable to avian theropods, pterosaurs and lizards. However, the number of well-studied Haman Formation sites is much greater than the Sagok Formation sites described here. We therefore consider that the differences in known ichnofaunas may be in part due to differential history of study. Differences in the preservation potential of small tracks may also be a factor. Therefore, we predict that the Sagok Formation has the potential to yield additional small tracks, especially bird and pterosaur tracks which are ubiquitous in the Cretaceous of Korea (see Ha et al. 2018). We therefore, currently do not consider the differences between the sauropod-and ornithopoddominated Sagok ichnofaunas and those from the Haman Formation to be worthy of detailed analysis until further research is completed.

Gait transformation in small Caririchnium trackways
The 14 ornithopod trackways from the Jeo-ri tracksite, with one exception (Otw5) are all larger than the two smaller ornithopod trackways from the Mancheon-ri site. The Mancheon-ri tracks indicate quadrupedal progression for parts of the registered trackways. This evidence allows two possible interpretations: 1) the trackmakers progressed quadrupedally throughout their movement across the area, but not all manus tracks were registered, 2) the trackmakers switched between bipedal and quadrupedal progression as facultative quadrupeds. As discussed below, evidence is stronger for the latter interpretation -that the preserved tracks represent trackmaker behaviour, not differential preservation. Mancheon-ri ornithopod trackways Otw1 and Otw2 are both illustrated (Figure 7) to show variable gait patterns including switching from bipedal to quadrupedal progression. Trackway Otw2 is the more easterly situated of the two Mancheon-ri trackways and it shows the simpler gait pattern among the two trackways described here. It represents the smaller of the two trackways (mean FL 9.9 cm): Table 2. Otw2 consists of 13 consecutive pes tracks in the sequence Rp1 (proximal) to Rp7 (distal) with Rp7 associated with a manus track (Rm7). The trackway shows a pattern of steady deceleration (Figure 7). For example, five of the first six 'proximal' paces are the longest (range 32.7-36.9 cm: mean 34.5 cm). By contrast the last six 'distal' paces (range 32.0-26.5 cm: mean 29.1 cm) are the shortest, with the final step (Lp6-Rp7) of 27.2 cm making the transition from bipedal to quadrupedal progression. Thus, the mean length of the six distal paces is 6.9% shorter than the six proximal steps (SI Figure 1). Another interesting feature of the trackway is that it is asymmetric with the mean length of the L-R paces of 29.6 cm compared with mean R-L paces of 32.9 cm. Alternating, irregular or asymmetric pattern of long and short paces (steps) do not necessarily affect the apparent regularity of the strides (S1 Figure 2) Trackway Otw1 is the more westerly situated of the two Otw trackways and it shows the more complicated gait pattern among the two trackways described here. It also represents the larger of the two trackmakers (FL 11.5 cm): Table 2. Otw1 consists of 17 consecutive pes tracks in the sequence Lp1 (proximal) to Rp8 (distal), with the proximal Lp1 to Lp5 sequence ending with tracks Rp4 and Lp5 situated side-by-side as if the trackmaker had stopped. In the remaining distal, eight-track part of the sequence (Lp6 to Rp8) five of the eight pes tracks are associated with manus tracks. Thus, it appears that after bipedal progression for seven paces, the trackmaker apparently paused to 'stand' and leave 'side-by-side' pes tracks Rp4 and Lp5. After this apparent pause, progression continued with registration of tracks Lp6 and Lm6, leading off a series of paces representing quadrupedal progression. In short, the trackway transition from bipedal to quadrupedal progression is marked by clear trackway evidence of a pause in progression. The mean length of the first seven paces representing bipedal progression is 29.1 cm compared with a mean length of 37.7 cm for the last seven paces representing quadrupedal progression: i.e., a mean reduction in pace length of ~5%. Unlike trackway Otw2 which exhibits the alternating short-long pace asymmetry, no such asymmetry is trackway recognisable in trackway Otw1.
The relationships between trackways Otw1 and Otw2 are interesting for the following reasons: (1) the two trackways are sub-parallel and both are traceable for about the same distance (~3.5 m): Figure 6. (2) Both trackways are oriented in the same direction (southward), with an inter-trackway spacing between ~1.0 m at the proximally-registered trackway portions (to the north) and diverging to a spacing of ~1.8 m at the distally registered trackway portions (to the south).
(3) Both trackways represent similar-sized trackmakers, foot lengths 9.9 and 11.5 cm for Otw2 and Otw1 respectively.  Thulborn (1990). (4) Both trackways indicate a transition from bipedal to quadrupedal progression accompanied by a measurable deceleration. Trackway Otw1 shows the transition in the mid-point of the preserved trackway, whereas trackway Otw2 shows the transition at the distal end.
It is not possible to infer whether the two trackmakers crossed the area at the same time or on occasions separated by minutes, hours or even days. The parallelism of trackways, especially when they represent trackmakers of similar sizes, are generally considered one possible line of evidence for social or gregarious behaviour: i.e., evidence that the trackmakers were travelling at the same time in Table 3. Mean track and trackway measurements from the Mancheon tracksite, based on data from Kim et al. (2021a) which presented all measurements of individual tracks comprising trackways. We have retained the trackway numbers presented in Kim et al. (2021a)  the same direction. The evidence that the two trackmakers were also decelerating and transitioning from bipedal to quadrupedal progression in this small area (~2.0 m wide and ~3.5 m long), is consistent with the suggestion that the two trackmakers were travelling at the same time with similar gaits and speed estimates differing by ~1.5 km/hr. Reports of dinosaur trackways indicating where an animal paused or stopped, leaving side-by-side footprints are very rare. One such example was reported and illustrated by Lockley et al. (2000, Figure 2) for a Therangospodus (theropod) trackway from the Upper Jurassic of Turkmenistan. When such a pause takes place and a trackmaker stands momentarily, it has the choice to begin the next step with either foot. Depending on which foot leads into the next step, the trackway may appear to show a continuous L-R-L-R sequence, or it may appear that a step in the sequence is 'missing': e.g., L-R-L-L-R as in the case illustrated here (Figure 7) where the sequence Lp4, Rp4, Lp5, Lp6 was recorded. Thus, the trackmaker came to a 'standing' position with the registration of Lp5 (beside Rp4). It then led off with the left foot to register Lp6.
Although large ornithopod tracks are common in the Cretaceous of Korea, as well as globally Kim et al., 2009;Lim et al., 2012), small ornithopod tracks are less common. Matsukawa et al. (1999) reviewed a large sample of ornithopod tracks from the Cretaceous of the western USA and reported a size (FL) range of 16.5 cm -55.0 cm for pes tracks. Since then, smaller tracks (FL ~ 14.4 cm) have been reported from the Cretaceous of the western USA (Lockley et al. 2021) as well as tracks with FL of ~13.1 cm from the Cretaceous of Germany (Hubner 2016;Richter and Boehme 2016). As noted by Lockley et al. (2021) there has been debate over the possibility that the shift from bipedal to quadrupedal progression might be size (age) related with smaller trackmakers tending to be bipedal and larger ones tending to quadrupedality (Norman 1985, 1989, Maidment and Barrett 2014. The data base to address this question is presently insufficient to suggest definitive conclusions. First the definition of small versus large ornithopods is not fixed. Matsukawa et al. (1999) suggested that three cohorts might be identified in the USA sample, with the smallest represented by trackmakers with footprint lengths 16.5 cm -21.7 cm. Using this as a general guide the Mancheon-ri trackmakers fall at the larger end of the grouping suggested by Matsukawa et al. (1999) and would also be designated as 'small' according to the arbitrary definition of Thulborn (1990): i.e., with FL <25.0 cm. Three of the present authors (KSK, JDL and MGL) are presently studying additional samples of small ornithopod tracks from the Cretaceous of Korea that will expand the database.
The Sagok Formation is considered equivalent to the Haman Formation in Haman, Namhae and Goseong counties. As briefly reviewed by Kim et al. (2021a)

Conclusions
The Jeo-ri and Mancheon-ri tracksites are important palaeontological (ichnological) destinations in the Uiseong County area in the province of Gyeongsangbuk-do. The Jeo-ri site was the first dinosaur tracksite to be designated a Korean Natural Monument (Number 373) in 1994. Both have been included in the recently designated Uiseong Regional Geopark, leading to a re-evaluation of the tetrapod ichnofaunas, summarised herein. The larger Jeo-ri site is notable for revealing at least 383 tracks resolved into 35 trackways dominated by 19 trackways representing sauropods (19 of 35 = 54%) with variable size range, and 14 representing medium sized ornithopods (14 of 35 = 40%), and only two recognisable theropod trackways.
The majority of trackways represent progression towards the north and northwest. The site is also notable for an architecturally striking roof built to protect the site from some of the effects of weathering.
The smaller Mancheon-ri site reveals only about ~115 tracks on several stratigraphic levels in a thin vertical sequence. Only two surfaces reveal well-defined trackways, one with a single sauropod trackway segment and another with three ornithopod trackways and one theropod trackway. The two smaller, sub parallel ornithopod trackways are of special interest as they both indicate deceleration by the trackmakers as they transition from bipedal to quadrupedal progression, possibly while travelling together. One indicates that the trackmaker paused or stopped to 'stand' registering side-by-side pes tracks. This pausing or 'standing' configuration is very unusual in the dinosaur track record and is evidently the only example reported for an ornithopod trackmaker.