Tridactyl Tracks Research Articles

Tridactyl dinosaur footprints from the Triassic Sambaíba formation of northern Brazil

Some new tridactyl footprints have been recorded in the Malhada Vermelha farm locality, municipality of Fortaleza dos Nogueiras, state of Maranhão, northern Brazil, from the Sambaíba Formation, Parnaíba Sedimentary Basin. The specimens are fifteen isolated, in situ, mesaxonic tridactyl tracks preserved in six sandstone slabs as concave epireliefs. Abundant MISS evidence is preserved in the track-bearing blocks. The footprints are referred to as Grallator isp., linking them with an theropodian origin. The footprint-bearing levels were accumulated in shallow environments influenced by a tidal flat. The occurrence and interpretation of these findings bring a new approach to sedimentary subenvironments in the Sambaíba Formation.

The oldest fossil bird-like footprints from the upper Triassic of southern Africa.

Footprint morphology reflects the anatomy of the trackmaker's foot and is direct evidence for the animal's behaviour. Consequently, fossil tracks can be used to infer ancient diversity, ethology, and evolutionary trends. This is particularly useful for deep-time intervals during which the early history of an animal group is reliant upon limited fossil skeletal material. Fossil tracks of early birds and theropods, the co-existing dinosaurian ancestors of birds, co-occur in the rock record since the Early Cretaceous. However, the evolutionary transition from dinosaur to bird and the timing of the birds' origin are still contested. Skeletal remains of the basal-most birds Aurornis, Anchiornis, Archaeopteryx and Xiaotingia are Middle to Late Jurassic, while tracks with tentative bird affinities, attributed to dinosaurs, are known from as early as the Late Triassic. Here, we present numerous, well-provenanced, Late Triassic and Early Jurassic tridactyl tracks from southern Africa, with demonstrable bird-like affinities, predating basal bird body fossils by c. 60 million years.

First Jurassic to earliest Cretaceous dinosaur footprints for Bolivia at the Castellón formation (Tacurú Group), Tarija

ABSTRACT Bolivia has an outstanding tetrapod ichnological record from the uppermost Cretaceous deposits plus a new Triassic locality recently reported. Here, we report a new ichnosite, the first for the Jurassic to earliest Cretaceous in the Castellón Formation (Tarija, Bolivia) bearing about 350 dinosaur tracks. With the exception of few tridactyl tracks, all exhibit sauropod characteristics. The exposed set consists of three mediumgauge, subparallel large quadrupedal trackways, with one trackway oriented in opposite direction to the other two. The best preserved trackway shows large pedes of about 95 cm and 75 cm in length and width, respectively. The trackmaker was about 3.80 m in height at the hip and walked at a speed under 5 km/h. Available evidence suggests that the producer of the more detailed trackway may be a member of non-Neosauropoda Eusauropoda, even if a titanosauriform producer cannot be discarded. Dozens of small-sized sauropod tracks, less than 15 cm in pes diameter, appear associated with two of the trackways. The distribution of these trackways provides elements to test gregariousness among trackmakers if a possible synchronism is accepted. Wanderings recognisable on the sediment surface suggest that they may collectively represent an ichnological example of herd behaviour.

Riches of the Roma valley: theropod and ornithischian tracks from the Early Jurassic southern Africa

ABSTRACT The Upper Triassic – Lower Jurassic Stormberg Group, main Karoo Basin, is notably rich in diverse dinosaur trace fossils, particularly in the Roma Valley of western Lesotho. Here, we document in detail, for the first time, the Mokhosi ichnosite (Roma Valley), initially reported simply as preserving tridactyl tracks. Thirty-five pes tracks were identified, predominantly preserved as bipedal and quadrupedal trackways attributable to theropod and ornithischian trackmakers. Three distinct morphotypes consisting of pes or manus-pes pairs were assigned to Anomoepus, Eubrontes and tentatively to Kayentapus. Our Morphotype III, although comparable to Kayentapus, preserves quantitative and qualitative features distinct from other large southern African Kayentapus-like tracks, and possesses some characteristics that lean to an ornithischian affinity rather than theropod. Ultimately, the Mokhosi ichnosite contributes to the diverse ichnological record of the Roma Valley, which now includes 15 ichnosites that preserve Anomoepus, Eubrontes, Grallator, Kayentapus and Trisauropodiscus. Furthermore, this site provides essential data for refining our understanding of Early Jurassic ornithischians in Gondwana, which are minor components of the trace- and body-fossil records.

Early Jurassic theropod elongate tracks with metatarsal marks from Yunnan, China

ABSTRACT Elongate tracks with metatarsal marks are a rare type of dinosaur track that have been identified in various locations around the world. These tracks have been attributed to both theropods and ornithischians, and the mechanism of their formation has remained elusive. In this study, we describe well-preserved elongate tracks with metatarsal marks from two adjacent track sites in the Lower Jurassic Fengjiahe Formation in Yunnan Province, China. These tracks occur together with ‘normal’ tridactyl tracks that lack a metatarsal mark. The tracks were produced by theropod dinosaurs and are consistent with the classic Lower Jurassic Eubrontes-Grallator-Kayentapus assemblage found in the United States. We propose that these elongate tracks are formed by deep penetrations of the foot in soft substrate, where sediment collapses above parts of the descending foot, leaving a shallow surface track that preserves a metatarsal mark. Our findings provide new insights into the locomotion and behaviour of Early Jurassic theropod dinosaurs and highlight the importance of Yunnan Province in the study of dinosaur tracks in China.

The Middle–Upper Jurassic dinosaur-pterosaur fauna in Shandong Province, China: Evidence from ichnology

Tracks previously examined between 2002 and 2015 from an incompletely-studied, and now partially lost tracksite site in the Santai Formation of Shandong Province were restudied based on new excavations of additional surfaces. In contrast to the previous reports of tridactyl tracks, including Grallator, the present study discovered an additional assemblage of unequivocal pterosaur tracks (Pteraichnus) and a possible didactyl deinonychosaurian track. The age of the Santai Formation is controversial but it is probably Late Jurassic, which corresponds to the epoch when pterosaur tracks appear worldwide. Age interpretations, based on palynology and isotopic data, tentatively suggests an earlier Middle-Late Jurassic age and might suggest that the pterosaurian tracks are as old or somewhat older than any previously reported.

First report of a Late Triassic dinosaur track from the Zigui Basin, Middle Yangtze region, China

Trace fossils offer a great potential to enhance our understanding of the rise of dinosaurs and their interactions with the environment. Here, we report a Rhaetian theropod footprint found in the Shazhenxi Formation of the Zigui Basin, representing the stratigraphically oldest dinosaur track recorded from the Middle Yangtze region and has great significance for understanding the Late Triassic theropods and their distribution across East Asia. The tridactyl track is assigned to cf. Eubrontes isp. and shows a similar morphology with some tracks from the Sichuan Basin, indicating that Eubrontes had a wider spatial distribution in the Upper Triassic than previously thought. This work highlights the great interest and importance of palaeoichnological prospecting in the Triassic deposits of the Zigui Basin.

The first record of dinosaur track from Hubei Province, Central China

ABSTRACT A newly discovered dinosaur tracksite in the Middle Jurassic Xietan Formation of the Zigui Basin, is the first reported from Hubei Province, China. Access to the site is difficult due to the steep inclination (~60°) of the track-bearing beds. The tracks are poorly preserved and occur in a fragmented mudstone substrate. However, it is possible to identify a sauropod trackway and isolated tridactyl (theropod) tracks, suggesting a saurischian dominated ichnofauna. The preserved sauropod trackway falls into the range of a typical wide gauge sequence and, together with the overall shape of the imprints and low heteropody, points to the ichnogenus Brontopodus. The tracks are of relatively small size and can possibly be attributed to juveniles of a large species or, alternatively, to adults of a small species of eusauropods. The tridactyl tracks are incomplete and cannot be assigned to a distinct ichnotaxon with certainty.

Early Jurassic dinosaur-dominated track assemblages, floristic and environmental changes in the Holy Cross Mountains region, Poland

The Early Jurassic succession of the Holy Cross Mountains region in Poland offers a rare opportunity to study ecosystem complexity during the evolution and diversification of early dinosaurs, especially herbivorous ones. The section consists of continental and coastal deposits containing fossil assemblages spanning nearly 25 My of changes in terrestrial plants and some groups of invertebrates and tetrapods. Based on macrofossils and pollen and spores, the broader characteristics of the flora in this succession are presented. The floral assemblages show typical Early Jurassic characteristics and contain lycopsids, sphenopsids, ferns, cycadaleans, bennettitaleans, gnetaleans and ginkgoaleans, as well as conifers, and are similar to other Hettangian–Toarcian floral successions in Europe, showing the presence of a vast coniferous forest dominated by Hirmeriella in the early Hettangian, replaced by ginkgophyte-dominated floras in younger stages and araucarian conifer-dominated forests in the late Pliensbachian. Dinosaurs are documented mainly from their trace fossils (tracks and coprolites). Six distinct track assemblages (stratigraphically separated ichnoassemblages) of different ages can be identified. Current evidence indicates that while Anomoepus tracks are abundant throughout the long Hettangian–late Pliensbachian interval, medium-sized to large ornithischian tracks do not occur below the lower–middle Hettangian transition zone, associated with the first major marine transgression in the region. Hettangian strata with different theropod tracks ( Grallator, Anchisauripus, Eubrontes, Kayentapus , cf. Megalosauripus ), small Anomoepus tracks, numerous medium-sized Anomoepus -like tracks, Moyenisauropus tracks, tetradactyl tracks of sauropodomorphs (cf. Pseudotetrasauropus ) and oval-shaped tracks of sauropods ( Parabrontopodus ) significantly contrast with the higher part of the Lower Jurassic succession (upper Pliensbachian Drzewica Formation and middle–upper Toarcian Borucice Formation) containing new types of medium-sized to large theropod tracks ( Therangospodus ), small and medium-sized bird-like tridactyl tracks (cf. Trisauropodiscus , cf. Anomoepus ), exceptionally large, oval-shaped sauropod tracks ( Sauropoda indet.), and new types of medium-sized and large ornithischian tracks (cf. Deltapodus , cf. Anomoepus ). This points to a noticeable difference between the Hettangian and late Pliensbachian–Toarcian dinosaur ichnofaunas and may facilitate the study of regional and global changes and correlations. Both the palaeofloras and dinosaur trace fossils document ecosystem diversity and ecosystem changes, presented here in review form. The nature of these changes requires more detailed study, but preliminary results suggest the occurrence of rather complex and pronounced transformations in the dinosaur communities of the Holy Cross Mountains region. Based on our observations, the most significant event in Early Jurassic ecosystems took place within the Hettangian (change in floristic composition, the emergence of new groups of dinosaurs), but we also found what we believe to be a record of a major faunal turnover across the late Pliensbachian–middle–late Toarcian interval.

Microbially induced sedimentary structures and the preservation of vertebrate tracks on the Colorado River delta in Lake Powell, Hite, Utah

Microbially induced sedimentary structures (MISS) increase the preservation potential of vertebrate and invertebrate ichnofossils. The Colorado River forms a delta in Lake Powell at Hite, Utah, and the deltaic shoreline provides a natural laboratory to examine the development of MISS and their influence on vertebrate track preservation. Two types of MISS were identified: pustular and blister. Pustular MISS occur in proximity to the June 2020 high water line. The pustular morphology is characterized by mm-scale small mounds, or pimple-like shapes. Field emission scanning electron microscopy (FESEM) examination identified preserved filamentous cyanobacteria intertwined with fine silt- and clay-sized sediment and well-preserved freshwater diatoms. Branta canadensis (Canada goose) tracks are well developed and they vary from single tridactyl tracks to trampled horizons. Blister MISS, in contrast to pustular MISS, are present in lower elevations, forming in deeper water, greater than 0.5 m. Blisters are mm- to cm-scale irregular mounds that consist of arching mats that are detached from the underlying sediment creating a pore space. Through time the blister mat mounds are destroyed by fragmentation due to desiccation combined with wind processes. FESEM and energy-dispersive spectroscopy system (EDS) analyses indicate the presence of filamentous cyanobacteria on the exterior and palisade Bacillus-type bacteria are in the interior of the blister arch, and gypsum crystals within the mat arch. Freshwater diatoms are present in both mat types. A single human track and multiple trackways of Canis latrans (coyote) were identified on the blister mats. Weakly impressed Canada goose tracks are present. Tracks cross cutting or modifying the pustular MISS have preserved MISS surface textures except in the heavily trampled areas, whereas tracks linked to the blister mat typically do not have reserved mat texture, and usually contain fragmented mat within the impression. Because of fluctuating lake levels and desiccation, these track types had a limited temporal window where they may be produced when moisture conditions permitted MISS development, about two months. Any vertebrates through the area out of the “track window” were not recorded in sediment and mat modification. Tracks imprinted on pustular MISS in lacustrine environments will have a high preservation potential if there are annual fluctuations in lake levels.

Theropod Tridactyl Tracks Across the Triassic–Jurassic Boundary in Southern Africa: Implications for Pedal Morphology Evolution

The end-Triassic mass extinction events mark a pivotal period in archosaur history, and have been proposed to contribute to the rise and dominance of dinosaurs throughout the Mesozoic. In southern Africa, the Triassic–Jurassic boundary is contained within the richly fossiliferous fluvio-lacustrine-aeolian deposits of the upper Stormberg Group in the main Karoo Basin. Due to an absence of high-resolution radioisotopic age constraints, the exact placement of the boundary remains difficult. The Stormberg Group theropod osteological record is limited to scarce, fragmentary material; therefore, the abundant Norian–Pliensbachian tridactyl tracks attributed to theropods are vital for unraveling theropod dinosaur evolutionary trends in southwestern Gondwana. This study considers over 200 upper Stormberg Group tridactyl tracks assigned to the Kayentapus-Grallator-Anchisauripus-Eubrontes (K-GAE) plexus, to quantify their morphological variation across a time span of ∼35 million years. Our findings show that within the upper Stormberg Group, and across the Triassic–Jurassic boundary, the younger tracks become larger, have a decreased mesaxony and a reduced digit III projection. This reduced emphasis of the medial digit is also observed across the K-GAE plexus, and for the individual ichnotaxa across time in the main Karoo Basin, e.g., Eubrontes tracks become less mesaxonic and have a reduced digit III projection higher up in the stratigraphy. This suggests that these morphological trends are not simply linked to size but may reflect a change in autopod morphology through time, which has implications for pedal functionality. Furthermore, being morphologically distinct from contemporaneous North American K-GAE tracks (e.g., reduced elongation and mesaxony, no correlation between digit divarication angles and size), these southern African footprints warrant further investigation.

North America’s largest assemblage of Late Jurassic dinosaur trackways, a new look at the Purgatoire Valley dinosaur tracksite (Dinosaur Lake), Morrison Formation, southeastern Colorado, United States

ABSTRACT The Purgatoire Valley dinosaur tracksite (‘Dinosaur Lake’) is North America’s largest assemblage of Late Jurassic dinosaur tracks. Roughly 1,300 tracks representing ~100 trackways were reported from a 5,600 m2 area in 1986. Extensive new excavations have revealed more than 800 additional tracks in a 2,600 m2 area. Less abraded tracks farther from the river channel, excavated below bed rock not alluvium, provide high-quality-of-preservation morphometric data. Sauropod (Parabrontopodus) trackways up to 88 m long, some with over 100 successive pes prints, comprise nearly 500 manus and pes tracks. Parallel sauropod trackways confirm previous interpretations of gregarious behaviour, now including a mixed herd of subadult and adult individuals. A preferred westward trackway progression trend likely suggests a single or short-lived episode of gregarious movement along a lake shoreline. Nearly 300 newly recorded tridactyl (theropod) tracks range from 25 to 40 cm in length, with several trackways exceeding 25 or more successive steps. Theropod tracks are assigned to ichnogenus Megalosauripus, also known from the Late Jurassic of Utah, Europe, Central Asia and North Africa. Other theropodan ichnogenera (Hispanosauropus and Therangospodus) from this epoch and region have not been identified. Cross-cutting (over-printing) trackway relationships help constrain the sequence of track registration events.

Dinosaur Tracks from the Lower Jurassic Lufeng Formation of Northern Central Yunnan, China

An increasing number of theropod-dominated tracksites have been reported from the Jurassic and Cretaceous of China. These include a significant number from the Lower Jurassic of the Lufeng Basin, famous for its Lufengosaurus fauna and known for a typical Lower Jurassic globally-distributed tetrapod footprint biochron. Here we report another localized theropod track occurrence regular of various scattered tracksites from the Lufeng Formation. The tracks are medium-sized tridactyl tracks from the basal member of the Zhangjia'ao Member, Lufeng Formation which shows an unusually wide divarication between the traces of digits III and IV, which suggest several possible interpretations.

Dinosaur footprints from the Early Jurassic of Le Mazel (Lozère, Southern France)

During the 20th century, the first dinosaur tracks of the Causses Basin were identified at Saint-Laurent-de-Trèves, in the Parc National des Cévennes (southern France). A recent excavation reveals a new theropod tracksite in the Hettangian deposits from Le Mazel, 2km from the historical tracksite at Saint-Laurent-de-Trèves. The tracks are here described combining a biometric approach and 3D imaging photogrammetry. The main track-bearing surface bears 64 in situ tridactyl footprints preserved as concave epireliefs. Two morphotypes were identified, a “Grallatorid” morphotype and a “Kayentapus” morphotype. Footprints belonging to the first morphotype are closely similar to Grallator lescurei, Grallator minusculus, and Grallator sauclierensis. This study shows the difficulty to distinguish quite similar tridactyl tracks from an ichnotaxonomic point of view and highlights the importance of detailed biometric comparisons. Tracks are preserved in a brown to yellowish dolomudstone showing abundant cryptalgal laminites and mud cracks. These deposits were accrued in shallow environments such as intertidal and supratidal zones of a tidal flat.

First report of deinonychosaurian trackway from the Cretaceous of Guizhou, China

The southern edge of Sichuan Basin has a long-standing folklore about the Tian Ji Stone, which actually tells of the theropod tracks. Here we describe a new Tian Ji track site named Xinglongwan in Chishui, Guizhou Province, China. Two kilometers away from the old site recorded in 2011, the later with cf. Irenesauripus isp. are morphologically different from the Xinglongwan theropod tracks. The tridactyl tracks from Xinglongwan site have been assigned to the cf. Eubrontes. Didactyl tracks in the Xinglongwan site, which are the first discovery of deinonychosaurian tracks in Guizhou Province, are assigned to the Velociraptorichnus. Both tracks were recorded in the report about ichnofauna in Jiaguan Formation, representing the diversity of theropod tracks in Sichuan Basin. The authors also briefly discuss the preservation mode and potential external-morphological changes of cf. Eubrontes and Velociraptorichnus from Xinglongwan site.

The smallest non-avian dinosaur track in China (Lower Jurassic, Sichuan Province)

ABSTRACT The smallest non-avian theropods have often attracted attention of palaeobiological and ichnological research. Here, we describe a diminutive tridactyl track (10.2 mm in length) from the Lower Jurassic Ma’anshan Member of the Ziliujing Formation, Wuli site, Sichuan Province, China. The Wuli specimen may be the smallest theropod track in the world. However, as with other diminutive tracks, it remains unresolved if it was made by a juvenile or by a small species. The body length of the trackmaker is estimated at 12 cm, equivalent to the size of a modern sparrow. Possibly the track belongs to a juvenile suggesting precociality or superprecociality.

Darting towards Storm Shelter: A minute dinosaur trackway from southern Africa

Theropod dinosaurs are considered the main terrestrial carnivores in the Jurassic and Cretaceous. Their rise to dominance has been linked to, among others, body size changes in their early history, especially across the Triassic–Jurassic boundary. However, to qualitatively assess such temporal trends, robust skeletal and trace fossil data sets are needed globally. The richly fossiliferous southern African continental rock record in the main Karoo Basin offers an unparalleled perspective for such investigations. Herein, by documenting a newly discovered Early Jurassic trackway of very small, functionally tridactyl tracks near Storm Shelter (Eastern Cape) in South Africa, the track record can be expanded. Based on ichnological measurements at the ichnosite and digital 3D models, the footprint dimensions (length, width, splay), locomotor parameters (step length, stride, speed), and body size estimates of the trackmaker are presented. In comparison to other similar tracks, these footprints are not only the smallest Grallator-like tracks in the Clarens Formation, but also the most elongated dinosaur footprints in southern Africa to date. The tracks also show that the small-bodied bipedal trackmaker dashed across the wet sediment surface at an estimated running speed of ~12.5 km/h. During the dash, either as a predator or as a prey, the trackmaker’s small feet sunk hallux-deep into the sediment. The tracking surface is overgrown by fossilised microbial mats, which likely enhanced the footprint preservation. Based on track morphometrics and the regional dinosaur skeletal record, the trackmakers are attributed to Megapnosaurus rhodesiensis (formerly Syntarsus rhodesiensis), a small-to-medium-sized, early theropod common in southern Africa.Significance:
 
 A newly discovered Early Jurassic theropod trackway in South Africa contains not only the smallest tracks in the Clarens Formation, but also the most elongated dinosaur footprints in southern Africa to date.
 The tracks show that the small bipedal trackmaker dashed across the wet sediment surface at an estimated running speed of ~12.5 km per hour.
 During the run, the trackmaker’s feet sunk so deeply into the sediment that even the forwards-directed halluces were impressed.
 
 Open data set: https://doi.org/10.6084/m9.figshare.13007240.v1

Lowermost Jurassic dinosaur ecosystem from the Bleymard Strait (southern France): sedimentology, mineralogy, palaeobotany and palaeoichnology of the Dolomitic Formation

AbstractWe report the first Hettangian theropod tracksite (~200 Ma) yielding a rich accumulation of plant remains from the Bleymard Strait (southern France). It constitutes an excellent opportunity to reconstruct lowermost Jurassic ecosystems hosting dinosaurs and which are still poorly documented in this area. Two morphotypes of tridactyl tracks are distinguished. They share similarities with Grallator and Kayentapus. Plant-bearing beds yield abundant leafy axes (Pagiophyllum peregrinum), male cones (Classostrobus sp.), wood (Brachyoxylon sp.) and pollen of conifers (Classopollis classoides). Sedimentological, petrological and mineralogical analyses demonstrated that, in the Dolomitic Formation from Bleymard, the palaeoenvironment progressively evolved from (1) a shoreface to a foreshore domain; to (2) a shallow environment that is restricted or occasionally open to the sea; then to (3) an intertidal to supratidal zone. The Hettangian theropod ecosystem of the Bleymard Strait was composed of tidal flats that were periodically emerged and bordered paralic environments inhabited by a littoral conifer-dominated forest in which Cheirolepidiaceae were the main component. The paucity of the palaeobotanical assemblage, as well as the xerophytic characteristics of Pagiophyllum, show that flora from Bleymard was adapted to withstand intense sunlight and coastal environments exposed to desiccant conditions coupled with salty sea spray, and dry conditions. These features are those of a conifer-dominated flora under a tropical to subtropical climate. The flora as well as the clay mineral analyses suggest contrasting seasons (cyclically dry then humid). This study supports that theropods were abundant and particularly adapted to this type of littoral environment bordering Cheirolepidiaceae-dominated forests.

Darting towards Storm Shelter: a minute dinosaur trackway from southern Africa

Theropod dinosaurs are considered the main terrestrial carnivores in the Jurassic and Cretaceous. Their rise to dominance has been linked to, among others, body size changes in their early history, especially across the Triassic–Jurassic boundary. However, to qualitatively assess such temporal trends, robust skeletal and trace fossil data sets are needed globally. The richly fossiliferous southern African continental rock record in the main Karoo Basin offers an unparalleled perspective for such investigations. Herein, by documenting a newly discovered Early Jurassic trackway of very small, functionally tridactyl tracks near Storm Shelter (Eastern Cape) in South Africa, the track record can be expanded. Based on ichnological measurements at the ichnosite and digital 3D models, the footprint dimensions (length, width, splay), locomotor parameters (step length, stride, speed), and body size estimates of the trackmaker are presented. In comparison to other similar tracks, these footprints are not only the smallest Grallator-like tracks in the Clarens Formation, but also the most elongated dinosaur footprints in southern Africa to date. The tracks also show that the small-bodied bipedal trackmaker dashed across the wet sediment surface at an estimated running speed of ~12.5 km/h. During the dash, either as a predator or as a prey, the trackmaker’s small feet sunk hallux-deep into the sediment. The tracking surface is overgrown by fossilised microbial mats, which likely enhanced the footprint preservation. Based on track morphometrics and the regional dinosaur skeletal record, the trackmakers are attributed to Megapnosaurus rhodesiensis (formerly Syntarsus rhodesiensis), a small-to-medium-sized, early theropod common in southern Africa.Significance: A newly discovered Early Jurassic theropod trackway in South Africa contains not only the smallest tracks in the Clarens Formation, but also the most elongated dinosaur footprints in southern Africa to date. The tracks show that the small bipedal trackmaker dashed across the wet sediment surface at an estimated running speed of ~12.5 km per hour. During the run, the trackmaker’s feet sunk so deeply into the sediment that even the forwards-directed halluces were impressed. Open data set: https://doi.org/10.6084/m9.figshare.13007240.v1

Morphological variations in dinosaur tridactyl tracks from the Candeleros Formation (Upper Cretaceous) of northwestern Patagonia, Argentina

Several dinosaur tridactyl tracks showing inter- and intra-trackways morphological variations from the Cenomanian Candeleros Formation of the Neuquén Basin, Argentina, have been documented. Footprints occur on three different stratigraphic levels and are impressed on medium-grained sandstone of fluvial origin. Level 1 includes deep tridactyl tracks with metatarsal impressions (average length of 31 cm) preserved as true tracks and undertracks that could have been generated due to simply sinking of the pes into a soft substrate and also probably by a continuous walk in a squatting position. Level 2 shows the largest tridactyl tracks (average length of 58 cm) recognized in this work, situated a few meters close to an already studied sauropod trackway. The different preservation between these bipedal and quadrupedal tracks could be explained due to different substrate properties and dissimilarities of the pedal shape between trackmakers. Level 3 comprises small to large tridactyl tracks (length from 6 to 34 cm) including intra-trackway morphological variation, that is interpreted as a result of changes in the substrate properties, mainly moisture content, along the tracking surface. Taking into account that the footprints studied here are poorly preserved, they were not assigned to any particular ichnotaxon. The large tridactyl tracks have been attributed to carcharodontosaurid theropod trackmakers while medium and small tracks to undetermined bipedal dinosaur. One pair of these large theropod tracks was closely documented on the same tracking surface of the aforementioned studied sauropod trackway, attributed to rebbachisaurids. This suggests that both carcharodontosaurid and rebbachisaurid trackmakers coexisted in the same habitats as the osteological record noted. This tracksite represents an example of the morphological variability of dinosaur tridactyl tracks controlled mainly by the substrate properties, and how an approach aimed at understanding footprint formation and preservation is necessary before beginning ichnotaxonomical studies, among others.