The Sichuan Basin in southwestern China is home to the most extensive theropod track record in the Lower Jurassic of China, comprising a range of minute-to medium-sized tracks that form the grallatorid-eubrontid (GE) plexus. The majority of these had previously been discovered in the Ma'anshan Member of the Ziliujing Formation. New material described herein is from the Wuli tracksite that suggests a flourishing paleoecological scene in a temporary waterfront habitat. Upon reviewing the GE plexus at different scales, we consider the locomotion style of these early theropod trackmakers, which likely included the 'grounded-running' gait of extant birds, as well as the possibility of a tail trace that may be related to intra- or interspecific interactions.

Late Triassic dinosaur skeletal records are missing in China, with only sparse dinosaur track occurrences documented in the southwestern and central regions. The Xujiahe Formation, situated along the northern margin of the Sichuan Basin, provides critical insights into the palaeoecosystems and sedimentary conditions of the region. A newly discovered Zilanba track site from the Fifth Member of the Xujiahe Formation near Guangyuan City, Sichuan Province, recorded ten tetrapod tracks. These small-sized tracks (majority of pes ranging 25-50 cm in length) comprise one trackway and four isolated tracks. Characterised by a medium gauge and possibly a low heteropody ratio (1: 2.3), although showing similarities with archosaurian tracks, they are tentatively attributed to basal sauropodomorphs. This site represents the ninth documented Triassic tetrapod track site in China and the third basal sauropodomorph track site of this period. This discovery enhances our understanding of the quantity and distribution of basal sauropodomorphs in Late Triassic of China. Furthermore, the Zilanba tracks provide new evidence supporting the previously proposed hypothesis of potential migration routes for basal sauropodomorphs from the western to the eastern Tethyan domain during this period.

The Sichuan Basin is a pivotal region for understanding the transition and evolution of Jurassic–Cretaceous dinosaur faunas in China. Despite a rich skeletal record, the quadrupedal track record from the Penglaizhen Formation remains scarce. This study reports a new sauropod tracksite discovered near Zhoujiagou in the Shuangliu District of Chengdu, Sichuan Province. The tracks occur within the upper strata of the Lower Cretaceous Penglaizhen Formation. The tracksite preserves at least three tracks constituting a possible trackway. These medium-sized impressions are characterized by a sub-circular morphology, a weak heteropody, and a potential wide-gauge trackway pattern. Based on these morphological attributes, the tracks are preliminarily referred to the Brontopodus morphotype. This discovery fills a critical gap in the sauropod ichnological record of the Penglaizhen Formation and provides evidence suggesting that mamenchisaurid dinosaurs, or their functional equivalents, persisted in the Sichuan Basin into the Early Cretaceous.

The evolution of a single-dentary-boned lower jaw and its secondary craniomandibular articulation between the dentary condyle and the squamosal glenoid has been regarded as a pivotal vertebrate innovation and defining mammalian trait1-7. Here we report two mammaliamorphs with novel shapes of secondary jaw joint, offering insight into the evolution of the mammalian jaw. The first, Polistodon8, a Middle Jurassic herbivorous tritylodontid with a relatively large body size and a lifestyle that is likely to have been fossorial, uniquely evolved a dentary-jugal articulation. The second, an Early Jurassic morganucodontan, exhibits a dentary-squamosal joint that lacks a bulbous condyle, supporting the hypothesis that the mammalian dentary condyle was formed by expansion of the lateral ridge of the dentary9. These diverse joints reflect repeated evolutionary experimentation in advanced cynodonts, in which secondary jaw joints arose independently7,10, and in which the load-bearing dentary-squamosal joint is a synapomorphy of mammaliaforms. Although body miniaturization might have driven this transformation11, our findings indicate that other factors were involved, such as jaw-muscle reorganization, feeding ecology and masticatory behaviour7,12-17. The ecomorphological diversity of these taxa suggest that phenotypic plasticity and environmentally induced morphological changes18-20 could have shaped jaw-joint evolution, emphasizing how ecological pressures and developmental flexibility guided the diversification of jaw structures in mammalian ancestors.

We report five new dinosaur track sites in Chaya County, about 120 km southeast of Changdu City. The track assemblages are dominated by sauropods (45 tracks), which have been identified tentatively as cf. Brontopodus. Also present are two thyreophoran trackways consisting of 13 tracks that show strong similarities with the ichnogenus Deltapodus, the potential trackmakers of which were probably stegosaurids. The sauropod tracks from the Chaya region are dominated by large tracks with different affinities if compared to those of the Changdu area. The isolated sauropod tracks from Changdu and Chaya regions show similar morphological patterns, but those from the Chaya region lack large scale tracks. This paper compares and discusses the known ichno and body fossil records of sauropods, theropods, and ornithischians from the Middle Jurassic of Yunnan, Sichuan, and eastern Tibet and their importance for our understanding of dinosaur faunas from this region. The absence of basal neornithischian records in the Yunnan and Changdu regions is likely a preservational bias but also an ecological pecularity cannot be completely excluded. The palaeogeographic position of the four sampled skeleton and track sites suggests the possible existence of a corridor through which faunal exchanges were taking place throughout the Jurassic.

Neosauropods were the dominant sauropod clade with a global distribution as early as the Late Jurassic. However, its distribution and biogeography in the Middle Jurassic are unclear due to the paucity of phylogenetic evidence for neosauropod taxa of this age. In China, the only reported Middle Jurassic neosauropod, the diplodocoid, has challenged the traditional East Asian Isolation Hypothesis for dinosaur paleobiogeography. Here, based on phylogenetic analysis including Dashanpusaurus dongi from the early Middle Jurassic of southwest China, we demonstrate that this taxon represents the earliest diverging macronarian as well as the stratigraphically lowest neosauropod globally. Our biogeographic analysis together with other geological evidence further indicates that neosauropods achieved a global distribution at least in the early Middle Jurassic while Pangaea was still a coherent landmass.

The identification of dinosaur tracks at a courtyard location in a restaurant in Leshan City, Sichuan Province, China became an international news story due to the unusual location of the discovery. Careful analysis of these 'restaurant tracks' indicates that they originate in the track-rich, Lower Cretaceous Jiaguan Formation, and are Brontopodus type sauropod tracks typical of the saurischian dominated Sichuan Basin ichnofauna of this epoch. Studies of the weathering of the Leshan Buddha at Mount Lingyun, a world heritage site only 5.5 km from the restaurant, indicate similar lithologies that allow estimation of weathering rates.

The sauropod genus Mamenchisaurus, from the Late Jurassic–Early Cretaceous of East Asia, has a convoluted taxonomic history. Although included in the first cladistic analysis of sauropods, only recently has the monophyly of Mamenchisaurus, and the anatomical diversity of the many penecontemporaneous East Asian eusauropods, been evaluated critically. Here, we re-describe the holotype and only specimen of M. sinocanadorum. Although the original diagnosis is no longer adequate, we identify several autapomorphies that support the validity of this species, including an elongate external mandibular fenestra and distinctive pneumatic structures on the cervical centra. We incorporate new data into a phylogenetic character matrix that also includes Bellusaurus and Daanosaurus, both of which are known only from juvenile material and are often hypothesized to be neosauropods (or close relatives thereof). We recover all species of Mamenchisaurus as part of a radiation of predominantly Middle–Late Jurassic East Asian eusauropods, but the genus is non-monophyletic, underscoring the need for further systematic revision of mamenchisaurid taxonomy. Analyses that score ontogenetically variable characters ambiguously recover Bellusaurus and Daanosaurus as juvenile mamenchisaurids, a hypothesis supported by several features that are unique to mamenchisaurids or exhibit little homoplasy, including anteriorly bifurcate cervical ribs. Finally, computed-tomography reveals extensive vertebral pneumaticity in M. sinocanadorum that is comparable to that of the largest sauropods, and updated scaling analyses imply a neck over 14 m long, rivalling estimates for other exceptionally long-necked sauropods. Previous work has suggested that the elongated cervical ribs of particularly long-necked sauropods such as M. sinocanadorum stabilized the neck by limiting its mobility. Given that extent of pneumaticity responds dynamically to a bone's habitual loading, we propose that long cervical ribs – and other structural modifications that limited flexibility – promoted the evolution of increasingly long necks by producing a more predictable biomechanical milieu amenable to increased pneumatization.

The Sichuan Basin, also known as the ‘Red Basin’, is famous for its abundance of Mesozoic dinosaur fossils, especially in the Zigong area during the Jurassic era; the Middle Jurassic Shunosaurus and the Late Jurassic Mamenchisaurus faunal assemblages are the most representative. The Qinglongshan dinosaur fossil site is located in Fuxing, to the northwest of Rong County, Zigong City. This new site is situated within the Middle Jurassic Xiashaximiao Formation, and geologically is roughly equivalent to the well-known Dashanpu dinosaur fossil site. More than 600 dinosaur fossils were found concentrated in the excavation area, including teeth; cervical, dorsal and caudal vertebrae; and various parts of appendicular skeletons. This fossil site is also most significant as it provides new information on non-avian dinosaur life during the poorly understood Middle Jurassic.

四川盆地的中生代陆相地层十分发育,盛产恐龙骨骼化石和足迹化石.自上个世纪六十年代在宜宾首次发现恐龙足迹化石以来,迄今盆地内已发现恐龙足迹化石点38处,其中侏罗纪恐龙足迹点16个,是我国侏罗纪恐龙足迹化石的代表性地区.本文从区域研究的角度出发,归纳了盆地已发现的恐龙足迹化石类型,分析了其地理分布和地层分布规律,重点介绍了三个代表性的侏罗纪恐龙足迹化石点的化石组合特征,提出了今后研究应重点关注的方向.

The Middle Jurassic lower Shaximiao Formation in Sichuan Province of south-western China has yielded a diverse terrestrial vertebrate fauna dominated by sauropod dinosaurs. However, many of these sauropods lack detailed descriptions or explicit phylogenetic diagnoses. Here, we present a comprehensive redescription of Dashanpusaurus dongi, a species of sauropod found only in the lower Shaximiao Formation. We define the revised autapomorphies of the species as follows: neural canals are sub-square in anterior dorsal vertebrae; the presence of a thin accessory lamina that contacts the prezygodiapophyseal and paradiapophyseal laminae of the middle dorsals, forming an angle of 75° to the horizontal; and four ridges on the anterodistal edge of the humerus. Often considered part of the epipophyseal-prezygapophyseal lamina, a strut invades the spinodiapophyseal fossa in the cervical and anterior dorsal vertebrae. Anatomical comparisons indicate that this feature was widespread among early-diverging Middle Jurassic eusauropod lineages. This comparative anatomical data provides an opportunity to revisit the phylogenetic position of Dashanpusaurus and the relationships of the neosauropod clade. Recovered as a macronarian, a better understanding of Dashanpusaurus dongi will allow for clarification of the origin, early evolution, and palaeogeographical distribution of neosauropods. This study also suggests that the diversity and dispersity of the neosauropod clade occurred much earlier than previously realized.

A Late Jurassic ichnofauna from the Suining Formation at the Yejipo site, Huangba Village, Sichuan Province has been locally known for its fossil footprints since the 1980s as the name 'Yejipo', meaning feral chicken/pheasant indicates. The best-preserved trackway represents a large theropod (mean footprint length 55.0 cm) assigned to Megalosauripus isp, with a length/width ratio of 1.4, and mesaxony index of 0.31. The tracks show the digit III/footprint length ratio of 0.60 typical of this ichnogenus. Two consecutive right footprints reveal an unusual digital pad trace pattern, exclusive of digit II metatarsal phalangeal pad giving a pad formula of 3-3-4 corresponding to digits II-III-IV rather than the typical 2-3-4 formula of theropods. As this formula can only be observed in the right, not the left, footprints, it is possible to suggest a pathological or congenital deformity. The assemblage also includes a typical elongate Grallator track (footprint length 13.8 cm, length/width 1.9). Other small tridactyl tracks are provisionally assigned to the ichnogenus Anomoepus. Collectively the ichno-assemblage is similar to others known from the Jurassic of China, although the occurrence of an anomalous Megalosauripus track is unusual.

A newly discovered saurischian dominated tracksite in the Lower Cretaceous Jiaguan Formation in southeastern Sichuan province reveals 13 sauropod trackway segments representing ichnogenus Brontopodus and three theropod trackways. This is a typical Type 1 Jiaguan Formation deposit dominated by tetrapod tracks with no significant tetrapod body fossils. The tracks occur in a river channel exposure of feldspathic quartz sandstone about 20–25 m wide and ~ 60 m long. The trackways are exposed on both banks but eroded away in the central channel area. The sauropod tracks represent relatively small animals with pes print lengths ranging from 24.5 cm to 33.9 cm. The theropod trackways include a large example (footprint length 46.5 cm with metatarsal traces) and two smaller parallel trackways with footprint lengths less than 20 cm. The author also discussed the erosion of tracks and trackways by water erosion, especially their morphological changes.

The Jiaguan Formation and the underlying Feitianshan Formation (Lower Cretaceous) in Sichuan Province yield multiple saurischian (theropod–sauropod) dominated ichnofaunas. To date, a moderate diversity of six theropod ichnogenera has been reported, but none of these have been identified at the ichnospecies level. Thus, many morphotypes have common “generic” labels such as Grallator , Eubrontes, cf. Eubrontes or even “ Eubrontes - Megalosauripus ” morphotype. These morphotypes are generally more typical of the Jurassic, whereas other more distinctive theropod tracks ( Minisauripus and Velociraptorichnus ) are restricted to the Cretaceous. The new ichnospecies Eubrontes nobitai ichnosp nov. is distinguished from Jurassic morphotypes based on a very well-preserved trackway and represents the first-named Eubrontes ichnospecies from the Cretaceous of Asia.

In recent years the number of track sites discovered and reported from the Lower Cretaceous Jiaguan Formation, Sichuan Basin has increased steadily. Here we report on the 20th and 21st sites which are situated in unusual locations in a cave and on a steep bedding plane surface in association with Tang Dynasty grottoes. The ichnofauna is represented by two small assemblages which are both theropod-dominated. Due to sub-optimal preservation, the tracks are identified only as grallatorid and small and larger eubrontid, with Paracorpulentapus also tentatively recognized.

The newly discovered Maoshajing tracksite in the Lower Jurassic Longtoushan Group of Guizhou Province, China is dominated by well-preserved medium-sized theropod tracks of the Grallator-Eubrontes plexus type, and associated with a few sauropod tracks. This saurischian dominated ichnofauna is typical of the Lower Jurassic biochron of China and elsewhere. It is also consistent with the sparse body fossil record, making it a type 2a deposit in which tracks are more abundant, and therefore also more important in providing a useful census of the tetrapod fauna. It is argued that small tracksite surfaces are more useful in ‘capturing’ (registering) evidence of small and potentially more active theropod movements than the activity of larger saurischians (sauropodomorphs) which may have been less abundant and less active in areas of any given size.

Tracks from two sites in the Middle Jurassic Xintiangou Formation in the Wuma Village area, Wuhuang Township, Zizhong have been known and intermittently studied and excavated since the 1980s. The track-bearing surfaces were exposed by a combination of natural weathering and deliberate excavation by residents in a rural agricultural area. The surfaces were used as “threshing floors” for the processing of agricultural crops in an area subject to weathering under a humid sub-tropical climatic regime. Despite the negative effects of weathering on the quality of track preservation, the sites are historically significant in Chinese ichnology as the type areas for many controversially named theropod ichnotaxa. Subsequent researchers challenged the ichnotaxonomy as provincial and over-split, suggesting that many of the tracks, belong to well-known Lower Jurassic ichnogenera. The present study reviews these two sites, providing new information, and confirming that the tracks belong to the ichnogenera Grallator, Eubrontes and Kayentpus which are typical of the globally widespread Lower Jurassic tetrapod biochron. This suggests the Middle Jurassic ichnofauna in Sichuan is like Lower Jurassic ichnofaunas elsewhere. Previous efforts to transfer the ichnospecies to globally, better-known ichnogenera were important in reducing ichnogenus diversity, but did not reduce ichnosepcies diversity. Herein the ichnotaxa are reviewed and it is shown that the ichnospecies names have no utility for comparative study or in assessing assemblage diversity, or biochron composition. It is therefore proposed that the multiple ichnospecies names proposed based on tracks from these two localities can mostly be accommodated under the labels Grallator isp. indet., and Eubrontes isp. indet.

The Zhaojue (ZJ) tracksites represent multiple steeply-inclined, track-bearing exposures in the clastic Feitianshan Formation of Sichuan Province that have been sequentially, excavated, mapped, expanded and destroyed, by quarrying, erosion or collapse, for almost three decades. The quarried area extends for more almost 1.0 km from north to south and ~ 0.5 km from east to west. Four important track-bearing surfaces have been identified and identified as ZJ-I, ZJ-II, ZJ-IIN and ZJ-III, some of which are newly exposed surfaces or expanded surfaces that were previously partially described. Others represent surfaces lost since they were first reported in papers published in 2014–2016. The ZJ-II site represents a hugely expanded continuation of a much smaller track-bearing surface described in 2014. It was mapped using drone technology, and now represents the largest tracksite in China, with a minimum count of 933 recognizable tracks, and the longest recorded sauropod and ornithopod trackways from China (~80 m and ~52 m respectively), which also reveal a pronounced change in the direction of trackmaker movement. The ZJ-II surface represents the best Zhaojue paleo-census sample giving a count of 68 individuals from 61 trackways (37 ornithopod, 10 theropod, 14 sauropod) and isolated tracks (representing 7 individuals). Thus, ornithopods (both large and small trackmakers) represent ~54% of the total number of trackways. The smaller ZJ-III surface was mapped using traditional methods, and reveals at least 6 ornithopod- and 4 theropod trackways. Both the ZJ-II and ZJ-III surfaces reveal parallel ornithopod trackways suggestive of social or gregarious behavior. The combined data from all four Zhaojue surfaces reveal a total of 1928 tracks, and include a few previously reported pterosaurs and theropod swim tracks. The Zhaojue quarry complex provide a good example of multiple track-bearing sites (surfaces) that require long term study and monitoring to extract as much trackway data as possible before in situ physical evidence is lost.

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.