Track Assemblage Research Articles

Lower Cretaceous sauropod trackways from Lishui City and an overview of dinosaur dominated track assemblages from Zhejiang Province, China

A relatively small number of tetrapod tracksites from Zhejiang Province fills out the fossil record from that region, which is also known to have yielded both saurischian (titanosauriform, coelurosaur) and ornithischian (basal ornithopod, ankylosaurian) body fossils as well as dinosaurian eggs. We use photogrammetry and 3D imaging to reinterpret the sauropod tracks from Lishui City, which revealed the existence of trackways. The track record from three documented sites in Zhejiang Province includes avian and non-avian theropod, sauropod, ornithopod and pterosaur tracks. Previous work showed that the purported new bird ichnospecies Dongyangornipes sinensis is a synonym of Uhangrichnus chuni, while we here consider Pteraichnus dongyangensis as a nomen dubium. Such “provincial ichnotaxonomy” may mask similarities in the ichnofauna across large regions. In fact, we show that the ichnofauna is similar to that found in the Early Cretaceous elsewhere in China.

Pleistocene animal communities of a 1.5 million-year-old lake margin grassland and their relationship to Homo erectus paleoecology

The ecological and selective forces that sparked the emergence of Homo's adaptive strategy remain poorly understood. New fossil and archaeological finds call into question previous interpretations of the grade shift that drove our ancestors' evolutionary split from the australopiths. Furthermore, issues of taphonomy and scale have limited reconstructions of the hominin habitats and faunal communities that define the environmental context of these behavioral changes. The multiple ∼1.5 Ma track surfaces from the Okote Member of the Koobi Fora Formation at East Turkana provide unique windows for examining hominin interactions with the paleoenvironment and associated faunas at high spatiotemporal resolution. These surfaces preserve the tracks of many animals, including cf. Homo erectus. Here, we examine the structure of the animal community that inhabited this landscape, considering effects of preservation bias by comparing the composition of the track assemblage to a skeletal assemblage from the same time and place. We find that the track and skeletal assemblages are similar in their representation of the vertebrate paleocommunity, with comparable levels of taxonomic richness and diversity. Evenness (equitability of the number of individuals per taxon) differs between the two assemblages due to the very different circumstances of body fossil versus track preservation. Both samples represent diverse groups of taxa including numerous water-dependent species, consistent with geological interpretations of the track site environments. Comparisons of these assemblages also show a pattern of non-random hominin association with a marginal lacustrine habitat relative to other vertebrates in the track assemblage. This evidence is consistent with behavior that included access to aquatic foods and possibly hunting by H. erectus in lake margins/edaphic grasslands. Such behaviors may signal the emergence of the adaptative strategies that define our genus.

Tetrapod track assemblages from Lower Cretaceous desert facies in the Ordos Basin, Shaanxi Province, China, and their implications for Mesozoic paleoecology

Tetrapod ichnofaunas are reported from desert, playa lake facies in the Lower Cretaceous Luohe Formation at Baodaoshili, Shaanxi Province, China, which represent the first Asian example of an ichnnofauna typical of the Chelichnus Ichnofacies (Brasilichnium sub-ichnofacies) characteristic of desert habitats. The mammaliomorph tracks, assigned to Brasilichnium, represent the first report of this ichnogenus from Asia. The assemblages also contain three different theropod trackway morphotypes: one very wide Magnoavipes-like morphotype, one relatively wide, broad-toed, small Eubrontes-like form with short steps and strides, and wide straddle, and an elongate morphotype (Sarmientichnus) with longer steps and narrower straddle representing a didactyl trackmaker, the latter being the first example of the enigmatic ichnogenus found outside its type area in Argentina. The Sarmientichnus occurrence, the first in Asia, has important implications, demonstrating that the trackmaker was not monodactyl, but didactyl with probable affinities to deinonychosaurians which are ichnologically well-represented in the Lower Cretaceous of Asia. Although morphologically distinctive, Sarmientichnus should be recognized as a “form” ichnotaxon compromised by suboptimal preservation. The combination of Brasilichnium isp., Sarmientichnus isp., and tridactyl theropod tracks, indicates mammaliomoprhs and small theropods, and is comparable to ichnofaunas from similar desert facies on other continents. Thus, Cretaceous desert ichnofaunas from China are consistent with global ichnofacies predictions.

Multiple parallel deinonychosaurian trackways from a diverse dinosaur track assemblage of the Lower Cretaceous Dasheng Group of Shandong Province, China

Many newly-discovered dinosaur tracksites have recently been reported from the Lower Cretaceous Dasheng Group of Shandong Province. These are proving valuable as tools for characterizing the fauna in deposits almost devoid of body fossils. Here we report on a new Cretaceous site, the 14th documented in recent years, with multiple track-bearing levels, that adds ∼300 tracks to a growing database. At least two morphotypes tentatively labelled as cf. Menglongpus isp., representing a deinonychosaur, and cf. Tatarornipes isp., representing an avian theropod, add to the list of at least seven named ichnogenera attributed to avian and non-avian theropods reported from the Dasheng Group in Shandong Province. Combined with two sauropodomorph and two ornithopod ichnogenera, and unnamed turtle tracks, the genus-level ichnodiversity (∼14) is one of the highest reported for any Cretaceous unit either regionally in China or globally.The tracks identified as cf. Menglongpus isp. occur in four parallel trackways indicating a group of small didactyl bipeds of inferred deinonychosaurian affinity. Despite the lack of body fossils from the Dasheng Group in Shandong Province, a high diversity of deinonychosaur body fossils is known from the contemporary Jehol Biota from northeastern China. This similarity underscores the importance of the Shandong track assemblage as indicators of regional, tetrapod biodiversity during the Cretaceous.

Diverse sauropod-theropod-dominated track assemblage from the Lower Cretaceous Dasheng Group of Eastern China: Testing the use of drones in footprint documentation

The use of drones in the exploration and documentation of track surfaces in steep terrain, otherwise only accessible by time intensive climbing activity, is tested. Location is the Nanquan site, one of many now known footprint localities from the Lower Cretaceous Dasheng Group that has been recently exposed by local industrial excavation. It reveals an ichnofauna of sauropod, theropod, and ornithopod tracks and trackways occurring at multiple stratigraphic levels (at least 10) in a thin sequence of fine grained purple mudstones with thin sandstone units that are steeply inclined by >45°. It was therefore necessary and most efficient to map the track-bearing surfaces using drone photography. The majority of track-bearing levels reveal sauropod tracks (cf. Brontopodus, cf. Parabrontopodus), which on some surfaces are very abundant. Large theropod tracks (cf. Grallator) and ornithopod tracks (Caririchnium) also occur, but only on single horizons. The ichnofauna is evidence of repeated activity by large dinosaurs in a fluvio-lacustrine floodplain setting susceptible to periodic desiccation. The Naquan site forms part of an extensive Dasheng Group outcrop belt with multiple tracks sites, most of these containing multiple track-bearing levels. As a result of the investigation, drone techniques can be recommended as an additional tool for quick documentation, in order to get a general overview and map of the track surface. Details are relatively distinct on the achieved photographs, however, a precise study still needs direct examination and documentation by classical outline drawings or photogrammetry.

Early Jurassic Batrachopus-rich track assemblages from interdune deposits in the Wingate Sandstone, Dolores Valley, Colorado, USA

Late Triassic and Early Jurassic tetrapod track assemblages are abundant and quite well documented from the respective Chinle and Glen Canyon groups of the Dolores Valley region of western Colorado and adjacent regions, especially eastern Utah. However, gaps still exist in our knowledge of the spatial and temporal distribution of representative ichnogenera. The stratigraphic distribution of track assemblages in the cliff-forming Wingate Sandstone Formation, the lower unit of the Glen Canyon Group, underlying the Kayenta and Navajo formations, is difficult to determine because almost all Wingate assemblages are known only from fallen blocks, originating from precipitous, vertical cliffs, which yield both dune and interdune ichnofaunas. Among the characteristic Lower Jurassic biochron ichnogenera Grallator, Eubrontes, Otozoum, Anomoepus and Batrachopus, in the Dolores Valley only Grallator is known abundantly, while Otozoum, and Batrachopus were previously known only from single occurrences, and Eubrontes and Anomoepus have yet to be reported. We here report two large, Batrachopus-rich assemblages that give new insight into the interdune paleoenvironments frequented by the Batrachopus trackmaker, traditionally regarded as a basal crocdylomorph, and the theropodan trackmaker of Grallator. Both assemblages contain the best-preserved and most abundant Batrachopus currently known, locally in high densities. Where individual trackways are clearly visible they indicate that the trackmakers had variable gaits. A third new assemblage containing Batrachopus from Salt Creek is also described, as is a fourth new assemblage from the Uncompahgre Plateau which yields moderately large theropod tracks (cf. Eubrontes), but no Batrachopus. Although diagnostic Late Triassic biochron ichnogenera like Brachychirotherium occur in basal units of the Wingate Sandstone, Batrachopus which is considered an Early Jurassic biochron ichnotaxon, occurs within the formation. Thus, vertebrate ichnotaxa help place the Triassic–Jurassic boundary within the Wingate Formation, shed light on their spatio-temporal distribution, and underscore their utility for paleoecological interpretation, in a unit devoid of tetrapod body fossils.

First reports of turtle tracks from the Williams Fork Formation (‘Mesaverde’ Group), Upper Cretaceous (Campanian) of western Colorado

Tetrapod footprints from the coal-bearing, Upper Cretaceous beds of Colorado, Wyoming and Utah, loosely known as the “Mesaverde” Group, have been reported and collected, mostly for Utah and Colorado institutions since the 1920s. However, it has only been in recent decades that the track assemblages have been reexamined in any detail. The results of such work indicate that the assemblages are more diverse than hitherto recognized. Here we report the first assemblages of turtle tracks that come from an important locality in the Williams Fork Formation in western Colorado, which also yields diverse dinosaur tracks. Collectively the turtle track-dominated assemblages reveal more than 150 swim tracks registered on a total surface area of ∼3 m2, indicating a density of ∼50 tracks/m2, and a fauna in which turtles were a significant component. The swim tracks mostly show strong preferred orientations suggesting the influence of directional currents. The co-occurrence of turtle tracks swim tracks and dinosaur tracks in the local facies indicates a mosaic of subaqueous and emergent wetland substrates consistent with the interpretation of these track-rich, coal- and plant-rich sequences as swampy, coastal plain habitats. Current evidence suggests these Upper Cretaceous tracks are typically larger than those known from the ‘mid’ and Lower Cretaceous in North America and elsewhere. Thus, the Williams Fork paleoenvironments may have represented settings conducive to habitation by large turtles.

Hominin track assemblages from Okote Member deposits near Ileret, Kenya, and their implications for understanding fossil hominin paleobiology at 1.5 Ma

Tracks can provide unique, direct records of behaviors of fossil organisms moving across their landscapes millions of years ago. While track discoveries have been rare in the human fossil record, over the last decade our team has uncovered multiple sediment surfaces within the Okote Member of the Koobi Fora Formation near Ileret, Kenya that contain large assemblages of ∼1.5 Ma fossil hominin tracks. Here, we provide detailed information on the context and nature of each of these discoveries, and we outline the specific data that are preserved on the Ileret hominin track surfaces. We analyze previously unpublished data to refine and expand upon earlier hypotheses regarding implications for hominin anatomy and social behavior. While each of the track surfaces discovered at Ileret preserves a different amount of data that must be handled in particular ways, general patterns are evident. Overall, the analyses presented here support earlier interpretations of the ∼1.5 Ma Ileret track assemblages, providing further evidence of large, human-like body sizes and possibly evidence of a group composition that could support the emergence of certain human-like patterns of social behavior. These data, used in concert with other forms of paleontological and archaeological evidence that are deposited on different temporal scales, offer unique windows through which we can broaden our understanding of the paleobiology of hominins living in East Africa at ∼1.5 Ma.

First reports of a distinctive theropod track assemblage from the Jinju Formation (Lower Cretaceous) of Korea provides strong correlations with China

Despite the extreme, well-documented abundance of tracks of herbivorous dinosaurs (ornithopods and sauropods), avian theropods and pterosaurs, from the Cretaceous of Korea the footprints of non-avian theropods have previously been reported only sporadically from the Cretaceous Gyeongsang Supergroup of Korea, without clear attribution to any ichnogenus. Here we report an assemblage of well-preserved theropod tracks from the Lower Cretaceous (?Aptian) Jinju Formation of the Jinju City area that contains distinctive ichnogenera including Grallator sensu lato, Corpulentapus and Asianopodus. These ichnotaxa were previously only known to co-occur in the Lower Cretaceous of China. In combination with other track evidence from the Lower Cretaceous of both China and Korea, this assemblage strengthens previous interpretations of the distinctive, apparently endemic nature of many East Asian dinosaurian ichnotaxa. The assemblage also helps refine debate over the age of track assemblages in the Lower Cretaceous of East Asia, and differences between assemblages from the lower and upper stages of the Lower Cretaceous.

Dinosaur footprint assemblage from the Lower Cretaceous Khok Kruat Formation, Khorat Group, northeastern Thailand

The Khok Kruat Formation is the upper part of the Khorat Group, which consists of upper Lower Cretaceous non-marine sedimentary rocks in northeastern Thailand. Many dinosaur footprints have been known from the upper Lower Cretaceous (Aptian–Albian) Khok Kruat Formation at the Huai Dam Chum (Tha Uthen) site, northeastern Thailand. Approximately 600 tracks occur in thin mudstone layer of the northern part of the outcrop at the Huai Dam Chum track site. Two types of footprints, small-sized theropod and crocodylomorph are imprinted with mud cracks and ripple marks on the thin mud layer. Most of footprints are referred to cf. Asianopodus, and are imprinted by small-sized theropoda, probably ornithomimosauria. Theropod tracks are mainly separated into two groups, Group A and Group B. From ichnological viewpoints, the small-sized theropod track assemblage indicates the herd behaviour and its idiosyncratic group composition. In particular, the histogram of size-frequency measurements of Group A shows the anomalous bimodal distribution. We consider that there are two hypotheses; the first one is due to the male-female difference, and the second is a result of the different growing stage.

Mid-Cretaceous dinosaur track assemblage from the Tongfosi Formation of China: Comparison with the track assemblage of South Korea

A Yanji Basin tracksite in the Cretaceous Tongfosi Formation in the Yanbian Korean Autonomous Prefecture, Jilin Province was reinvestigated twenty years after the original study.The re-examination confirms the presence of tracks tentatively referred to ornithopods and theropod tracks including several not previously reported. In addition to the main track-bearing level, a second footprint horizon was identified from which a probable ornithopod track was collected. Some of the formerly identified tracks were documented using photogrammetry, whereas others that had been collected, eroded, buried or obscured by dense vegetation. The age of the track-bearing beds is inferred to be late Albian to early Cenomanian. Comparison with track-bearing units of the same age in Shandong, China, and Korea indicated quite different compositions of track assemblages. In the case of the Korean sites the differences may be facies related. While the Korean ichnofauna is characterized by the co-occurrence of ornithopod, sauropod and tridactyl theropod tracks with didactyl dromaeosaurid, Minisauripus (small theropod), pterosaur and avian tracks, the latter four are absent in the Tongfosi assemblage. This could reflect a restricted environment being not favourable for activities of these trackmakers or simply a preservational bias.

A dinosaur track assemblage from the Upper Hettangian (Lower Jurassic) marginal-marine deposits of Zapniów, Holy Cross Mountains, Poland

Upper Hettangian (Lower Jurassic) marginal-marine Przysucha Ore-bearing Formation exposed at Zapniow mine and clay-pit (northwestern part of the Holy Cross Mountains area, central Poland) revealed an interesting assemblage of dinosaur tracks. Although mostly yielding poorly preserved and isolated tracks probably left in shallow water conditions, the site nevertheless indicates a diversity of early saurischian (theropods and sauropodomorphs) and ornithischian (thyreophorans) dinosaur trackmakers. This new assemblage is partly consistent with the Lower-Middle Hettangian ichnorecord from the same region. The tracks are preserved in sediments of a barrier-foreshore origin within a barrier/lagoonal depositional system, belonging to the highstand systems tract, located below a marked erosional surface (sequence boundary), which is associated with a substantial fall in sea level at the end of Hettangian times. Here we described all previously and newly collected or observed in the field dinosaur tracks from both surface and underground exposures at Zapniow. Four ichnospecies: Grallator isp., Anchisauripus isp., cf. Tetrasauropus isp., and cf. Anomoepus isp. were identified. The theropod and ornithischian tracks show distinct similarities to those described from the richest in this region and most famous Gliniany Las dinosaur track assemblage, in age approximately coeval to Zapniow. Two sizes of theropod tracks (small and medium) indicate the presence of two different size classes or species of predators in this area. The described cf. Tetrasauropus isp. from Zapniow is the first unquestioned evidence of basal sauropodomorphs in the Upper Hettangian of the Holy Cross Mountains and first record of this ichnotaxa in the Lower Jurassic of Poland. Additionally, two theropod trackways ( Anchisauripus isp.) show evidence for trotting. The new finds suggest similarities between marginal-marine environments (delta-plain and foreshore-barrier/lagoon lithofacies) association of dinosaurs containing low-browsing thyreophorans accompanied by small or juvenile sauropodomorphs and small to medium sized theropods. Presence of the ornithischian footprints suggests their prominent role as a major component in Middle-Upper Hettangian dinosaur faunas in marginal-marine environments dominating in the region

Middle-Upper Triassic and Middle Jurassic tetrapod track assemblages of southern Tunisia, Sahara Platform

Three tetrapod track assemblages from the early-middle Mesozoic of southern Tunisia are reported. The strata exposed at the Tejra 2 clay-pit near the Medenine and Rehach site, located in the vicinity of Kirchaou, contain the first tetrapod tracks found in the Triassic of Tunisia. The Middle Jurassic (early Aalenian) dinosaur tracks are reported from the Mestaoua plain near Tataouine. In the Middle Triassic outcrop of the Tejra 2 clay-pit, tridactyl tracks of small and medium-sized dinosauromorphs, were discovered. These tracks represent the oldest evidence of dinosaur-lineage elements in the Triassic deposits of Tunisia. Similar tracks have been described from the Middle Triassic of Argentina, France and Morocco. An isolated set of the manus and pes of a quadrupedal tetrapod discovered in Late Triassic Rehach tracksite is referred to a therapsid tracemaker. The Middle Jurassic deposits of the Mestaoua plain reveal small and large tridactyl theropod dinosaur tracks (Theropoda track indet. A-C). Based on comparison with the abundant record of Triassic tetrapod ichnofossils from Europe and North America, the ichnofauna described here indicates the presence of a therapsid-dinosauromorph ichnoassociation (without typical Chirotheriidae tracks) in the Middle and Late Triassic, which sheds light on the dispersal of the Middle-Upper Triassic tetrapod ichnofaunas in this part of Gondwana. The reported Middle Jurassic ichnofauna show close similarities to dinosaur track assemblages from the Lower and Middle Jurassic of northwestern Africa, North America, Europe and also southeastern Asia. Sedimentological and lithostratigraphic data of each new tracksite have been defined on published data and new observations. Taken together, these discoveries present a tantalizing window into the evolutionary history of tetrapods from the Triassic and Jurassic of southern Tunisia. Given the limited early Mesozoic tetrapod record from the region, these discoveries are of both temporal and geographic significance.

A revision of tetrapod footprints from the late Carboniferous of the West Midlands, UK.

A series of sandstone slabs from Hamstead, Birmingham (West Midlands, UK), preserve an assemblage of tetrapod trackways and individual tracks from the Enville Member of the Salop Formation (late Carboniferous: late Moscovian–Kasimovian). This material has received limited previous study, despite being one of the few British sites to preserve Carboniferous tetrapod footprints. Here, we restudy and revise the taxonomy of this material, and document it using 3D models produced using photogrammetry. The assemblage is dominated by large tracks assigned to Limnopus isp., which were made by early amphibians (temnospondyls). A number of similar but smaller tracks are assigned to Batrachichnus salamandroides (also made by temnospondyls). Dimetropus leisnerianus (made by early synapsids) and Dromopus lacertoides (made by lizard-like sauropsids such as araeoscelids) are also present. This ichnofauna contrasts with a slightly stratigraphically older, more extensive and better-studied assemblage from Alveley (Shropshire), which is dominated by small amphibians with relatively rare reptiliomorphs, but which lacks Dromopus tracks. The presence of Dromopus lacertoides at Hamstead is consistent with the trend towards increasing aridity through the late Carboniferous. It is possible that the assemblage is the stratigraphically oldest occurrence of this important amniote ichnotaxon.

Late Cretaceous ornithopod-dominated, theropod, and pterosaur track assemblages from the Nanxiong Basin, China: New discoveries, ichnotaxonomy, and paleoecology

Re-examination of the Late Cretaceous Yangmeikeng tracksite, in the Zhutian Formation (Nanxiong Group) near Nanxiong, Guangdong Province, China, has led to the documentation of over 30 vertebrate tracks. The track assemblage is dominated by large and small ornithopod tracks. The larger ornithopod tracks have been assigned to Hadrosauropodus nanxiongensis and Hadrosauropodus isp. indet. The smaller ornithopod tracks are consistently incomplete, showing only three pes digit traces, without heel or manus impressions. For this reason the smaller tracks probably represent pes tracks penetrating from a higher layer, and therefore have not been assigned to any particular ichnotaxon. Previous photography at Yangmeikeng site confirms the presence of at least one small Wupus-like theropod track and a Pteraichnus-like pterosaur pes track. Large enigmatic didactyl tracks could be of deinonychosaurian affinity, but are more likely the poorly preserved prints of a tridactyl theropod trackmaker. The Nanxiong dinosaur tracks and skeleton records represent the most important and diverse ichnofauna from Upper Cretaceous strata of South China, and can be compared with the Shandong and Heilongjiang Late Cretaceous faunas. The composition of the ichnofauna, is significant because it reflects a diverse tetrapod community with hadrosaurs, avian theropods, non-avian theropods and pterosaurs, a co-occurrence not evident from the skeletal record of this region. From a global perspective this assemblage permits a unique insight into archosaur communities and interaction of animals in a typical Late Cretaceous lakeshore environment. Non-avian theropods may have been attracted by the other groups that were considered as a potential prey.

A Dinosaur Ichnocoenosis from the Waterberg Plateau (Etjo Formation, Lower Jurassic), Namibia

ABSTRACTAbout a hundred dinosaur tracks, mostly preserved as isolated footprints, have been recorded at a single site within the borders of the Waterberg National Park, Otjozondjupa Region, north-central Namibia. They are found in an interdune setting within the Lower Jurassic Etjo Formation and represent medium-sized theropods with slender digits and high projection of digit three. From an ichnotaxonomic point of view, the Namibian tracks are intermediate in morphology between Grallator (which is known to occur at other localities within the same Etjo Formation) and Anchisauripus, being otherwise in a size range that is usually considered typical for the latter ichnotaxon or even for Eubrontes. The Waterberg tracks do not match the allometric growth model proposed by Olsen et al. (1998) for the Early Jurassic theropod track assemblage of the North American Connecticut Valley, and they highlight the difficulties of consistently discriminating between theropod ichnotaxa in the Grallator-Anchisauripus-Eubrontes plexus. The Waterberg ichnosite adds important data to our understanding of the ichnological diversity of the Etjo Formation, raising to three the dinosaur localities in Namibia with revised and updated ichnofaunas. The dinosaur ichnofauna from Namibia, of which the Waterberg tracksite is a basic component, shows high ichnotaxonomic similarity with coeval assemblages from the northern hemisphere. This points to an overall homogeneity of the global ichnofaunistic composition, even at lower latitudes.

Behaviour of Dinosaurian Track-Makers in the Winton Formation (Cretaceous, Albian–Cenomanian) at Lark Quarry, Western Queensland, Australia: Running or Swimming?

ABSTRACTA remarkable assemblage of dinosaur trackways in the Winton Formation (Albian–Cenomanian) at Lark Quarry, in western Queensland, Australia, has long been regarded as evidence of a stampede involving small theropods, whose tracks were classified in the ichnogenus Skartopus, and small ornithopods, whose tracks represented a second ichnogenus, Wintonopus. However, one recently-published study has claimed that existing interpretation of Lark Quarry is incorrect: it maintains that all the track-makers were ornithopods, that the ichnogenus Skartopus is a variant form of Wintonopus, and that most of the Lark Quarry track-makers were not running but more probably swimming downstream in a current of water. Those iconoclastic claims are investigated here and shown to be untenable. They derive from overgeneralized interpretation of the Lark Quarry track assemblage and invoke ad hoc auxiliary hypotheses which are either untestable or demonstrably incorrect. Closer inspection of the evidence underpinning those claims corroborates the existing interpretation of Lark Quarry as the site of a dinosaurian stampede and confirms the validity of the original distinction between theropod tracks (Skartopus) and ornithopod tracks (Wintonopus).

A theropod track assemblage including large deinonychosaur tracks from the Lower Cretaceous of Asia

A total of more than 40 tridactyl and didactyl tracks were preserved as natural casts on four fallen blocks of sandstone representing the Lower Cretaceous Jiaguan Formation of Gulin County in southeastern Sichuan Province, China. While several trackways can be distinctly followed, others are isolated imprints only. All have been flattened by overburden pressures. Tridactyl tracks are present with three size-classes being <10 cm, 10–20 cm and >20 cm in length. Morphologically they are similar to the ichnogenus Eubrontes, considering the relatively weak mesaxony. Eight of the tracks on one of the blocks are clearly didactyl and are here interpreted as representing large and medium sized dromaeosaurids. The largest track is about ∼30 cm long and comparable in size to the type of Dromaeopodus (∼28 cm), from the Lower Cretaceous of Shandong Province, which was the largest dromaeosaurid track previously reported. This report adds new data to the growing number of dromaeosaurid tracksites reports from China, and from the Jiaguan Formation, suggesting that this theropod group had a preference for fluvial paleoenvironments.

Saurischian track assemblages from the Lower Cretaceous Shenhuangshan Formation in the Yuanma Basin, Southern China

Cretaceous dinosaur tracks from Hunan Province are historically significant as the basis for three ichnotaxa: Xiangxipus chenxiensis, Xiangxipus youngi, and Hunanpus jiuquwanensis all representing theropodan tracks, described from a single site in 1982. Although the type locality has since been destroyed, the type specimen and replicas remained available for restudy in 2006, when paratype Hunanpus tracks and sauropod footprints were described from a second, nearby locality. Material from both localities is here re-described in detail. It is proposed that while Xiangxipus chenxiensis can be regarded as a distinct ichnospecies, probably representing an ornithomimid trackmaker, Xiangxipus youngi cannot be accommodated in the same ichnogenus. We consider it similar to the ichnogenus Wupus from the Lower Cretaceous of Sichuan Province, and therefore of possible avian affinity. We also find no justification for regarding Hunanpus jiuquwanensis as generically distinct from the widespread ichnogenus Grallator, and therefore rename it Grallator jiuquwanensis comb. nov. The Hunan track record is generally consistent with the sparse record of theropod skeletal remains in the province, but adds evidence of sauropods that was previously lacking.

Digit-only sauropod pes trackways from China--evidence of swimming or a preservational phenomenon?

For more than 70 years unusual sauropod trackways have played a pivotal role in debates about the swimming ability of sauropods. Most claims that sauropods could swim have been based on manus-only or manus-dominated trackways. However none of these incomplete trackways has been entirely convincing, and most have proved to be taphonomic artifacts, either undertracks or the result of differential depth of penetration of manus and pes tracks, but otherwise showed the typical pattern of normal walking trackways. Here we report an assemblage of unusual sauropod tracks from the Lower Cretaceous Hekou Group of Gansu Province, northern China, characterized by the preservation of only the pes claw traces, that we interpret as having been left by walking, not buoyant or swimming, individuals. They are interpreted as the result of animals moving on a soft mud-silt substrate, projecting their claws deeply to register their traces on an underlying sand layer where they gained more grip during progression. Other sauropod walking trackways on the same surface with both pes and manus traces preserved, were probably left earlier on relatively firm substrates that predated the deposition of soft mud and silt . Presently, there is no convincing evidence of swimming sauropods from their trackways, which is not to say that sauropods did not swim at all.