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Yangchuanosaurus
Temporal range: 168.3–145 Ma
Y. shangyouensis skeleton displayed in Hong Kong Science Museum
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Metriacanthosauridae
Genus: †Yangchuanosaurus
Dong et al., 1978
Type species
†Yangchuanosaurus shangyouensis
Dong et al., 1978
Other species
  • †Y.? hepingensis
    (Gao, 1992)
  • †Y.? zigongensis
    (Gao, 1993)
Synonyms
Synonyms of Y. shangyouensis
  • Yangchuanosaurus magnus
    Dong, Zhou & Zhang, 1983
  • Szechuanosaurus "yandonensis"
    Dong et al., 1978
  • "Szechuanoraptor dongi"
    Chure, 2001
  • Metriacanthosaurus shangyouensis
    Paul, 1988
Synonyms of Y.? zigongensis
  • Szechuanosaurus zigongensis
    Gao, 1993
  • Metriacanthosaurus carpenteri
    Paul, 1988

Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China from the Middle Jurassic to Late Jurassic periods (Bathonian to Tithonian stages), and was similar (although slightly larger) in size and appearance to its North American and European relative, Allosaurus. Yangchuanosaurus hails from the Upper Shaximiao Formation and was the largest predator in a landscape that included the sauropods Mamenchisaurus and Omeisaurus and the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. This theropod was named after the area in which was discovered, Yongchuan, in China.

Discovery and species

[edit]
Mounted skeleton of Y. zigongensis, Delaware Museum of Natural History

Dong et al. (1978) named Yangchuanosaurus shangyouensis on the basis of Municipal Museum of Chongqing 00215, a complete skull and skeleton which was collected from the Shangshaximiao Formation, near Yongchuan, Yongchuan District, Sichuan. It dates to the Oxfordian stage of the Late Jurassic period, about 161.2 to 157.3 million years ago. It was discovered in June 1977 by a construction worker during the construction of the Shangyou Reservoir Dam. A second species from the same locality, Y. magnus, was named by Dong et al. (1983) on the basis of CV 00216, another complete skull and skeleton. A detailed revision of tetanuran phylogeny by Carrano, Benson & Sampson (2012) revealed that both species are conspecific. Dong et al. (1978) and Dong et al. (1983) differentiated these species primarily on the basis of size. In addition, Dong et al. (1983) noted that the maxilla of Y. magnus has an additional fenestra within the antorbital fossa, whereas Y. shangyouensis possessed only a fossa in this location. However, it is considered to be an intraspecific, possibly ontogenetic, variation. Furthermore, the apparent difference in cervical vertebral morphology can be explained by comparing different positions within the column. Hence, the holotypes of the two species of Yangchuanosaurus are effectively identical, and their codings are identical in Carrano et al. (2012) matrix.[1] Gregory S. Paul (1988) regarded this genus as a synonym of Metriacanthosaurus, but this has not been supported.[2]

Additional specimens

[edit]
Life reconstruction of Y. shangyouensis

Y.? hepingensis is a species named by Gao in 1992,[3] but it was subsequently referred to as a species of Sinraptor.[4] However, the identity of this species within Sinraptor is questioned by other paleontologists,[1][5] and Rauhut and colleagues included this species within Yangchuanosaurus based on their phylogenetic analysis in 2019 and 2024 respectively.[6][7]

Carrano et al. (2012) assigned a third specimen to Y. shangyouensis. CV 00214 is represented by a partial postcranial skeleton lacking the skull. It was collected in the Wujiaba Quarry, near Zigong city, Sichuan, from the lower part of the Shangshaximiao Formation. CV 00214 was initially listed by Dong et al. (1978) in a faunal list as a new species of Szechuanosaurus, Szechuanosaurus "yandonensis". There is no description or illustration of it, making S. "yandonensis" a nomen nudum. Later, Dong et al. (1983) described it, and assigned it to Szechuanosaurus campi, a dubious species which is known only from four teeth. Carrano et al. (2012) noted that CV 00214 can't be assigned to S. campi because the holotype materials of S. campi (IVPP V.235, V.236, V.238, V.239; teeth) are non-diagnostic and no teeth are preserved in CV 00214. A recent restudy of CV 00214 by Daniel Chure (2001) concluded that it represented a new taxon, informally named "Szechuanoraptor dongi", into which Szechuanosaurus zigongensis should also be subsumed. However, Carrano et al. (2012) suggested that CV 00214 and "S." zigongensis cannot be cospecific as there are no autapomorphies shared between them, and the latter derives from the underlying Xiashaximiao Formation. A phylogenetic analysis found CV 00214 to be most closely related to Y. shangyouensis, and thus the former is assignable to it. Furthermore, Szechuanosaurus zigongensis was found to be closely related to Y. shangyouensis and therefore was designated as a new species of Yangchuanosaurus,[1] though this has been considered questionable by Rauhut and colleagues.[6][7]

Y.? zigongensis is known from four specimens including ZDM 9011 (holotype), a partial postcranial skeleton; ZDM 9012, a left maxilla; ZDM 9013, two teeth and ZDM 9014, a right hind limb. It was first described by Gao (1993), and all specimens were collected from the Middle Jurassic Xiashaximiao Formation in the Dashanpu Dinosaur Quarry of Zigong, Sichuan.[8]

Another informal species, Yangchuanosaurus "longqiaoensis", was briefly mentioned in a faunal listing of the Penglaizhen Formation (initially believed to date to the Late Jurassic but is probably Early Cretaceous (Berriasian – Valanginian) in age)[9] by Li, Zhang and Cai (1999).[10] However, since it was published solely in a faunal list and not described in detail, it is a nomen nudum and is questionably referable to Yangchuanosaurus.[11]

Description

[edit]
Size of two Y. shangyouensis specimens compared to a human

The type specimen of Y. shangyouensis had a skull 82 centimeters (2.69 ft) long, and its total body length was estimated at 8 meters (26 ft).[12] Another specimen, assigned to the new species Y. magnus, was even larger, with a skull length of 1.11 meters (3.6 ft).[13] It may have been up to 10.8 meters (35 ft) long, and weighed as much as 3.4 metric tons (3.7 short tons).[2] Gregory S. Paul suggested that these are the same species and gave a length of 11 meters (36 feet) and a weight of 3 metric tons (3.3 short tons).[14] There was a bony ridge on its nose and multiple hornlets and ridges, similar to Ceratosaurus and Tameryraptor.

Yangchuanosaurus was a large, powerful meat-eater. It walked on two large, muscular legs, had short arms, a strong, short neck, a big head with powerful jaws, and large, serrated teeth. It had a long, massive tail that was about half of its length. The first digit of its foot was a small dewclaw. The three outer toes were used to bear weight and each was equipped with a large claw.

Classification

[edit]
Mounted skeletons of Yangchuanosaurus and Tuojiangosaurus, Beijing Museum of Natural History
Life reconstruction of Y. shangyouensis

A phylogenetic analysis by Carrano et al. (2012) found Yangchuanosaurus to be the basalmost known metriacanthosaurid and the only non-metriacanthosaurine metriacanthosaurid. The cladogram presented below follows their study.[1]

Orionides

The cladogram presented below follows Zanno & Makovicky (2013).[5]

Allosauroidea

In 2019, Rauhut and Pol included Y.? hepingensis as a species of Yangchuanosaurus, while Y? zigongensis was recovered as a metriacanthosaurid not closely related to Yangchuanosaurus in their phylogenetic analysis.[6] In 2024, Rauhut and colleagues, the describers of Alpkarakush, included both Y. shangyouensis and Y.? hepingensis within Yangchuanosaurus but recovered Y.? zigongensis outside the genus as a basal tetanuran of uncertain taxonomic position based on their phylogenetic analysis.[7]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Yangchuanosaurus

View on Grokipedia
from Grokipedia
Yangchuanosaurus is an extinct of large metriacanthosaurid theropod that lived during the , approximately 160 to 155 million years ago, in what is now Sichuan Province, . This bipedal carnivore was an , measuring up to 10 meters in length and weighing around 3 tonnes, with a robust build featuring a large equipped with serrated, dagger-like teeth for tearing flesh, forward-facing eyes for , and powerful hind limbs for swift movement. The includes a single valid , the Y. shangyouensis, described in 1978 based on a nearly complete discovered in 1977 during construction at the Shangyou Reservoir in Yongchuan County; a larger specimen from the Upper , once classified as Y. magnus in 1983, is now considered synonymous with Y. shangyouensis. These dinosaurs inhabited a subtropical environment rich in rivers and forests, where they likely preyed on large herbivores such as sauropods like Mamenchisaurus. Classified within the superfamily Allosauroidea, Yangchuanosaurus shares similarities with North American allosaurids but represents a distinct Asian lineage of large theropods, providing key insights into the diversity and evolution of predators in eastern . Fossils, including skulls, vertebrae, and limb bones, have been recovered primarily from the Shangshaximiao Formation, highlighting its role as one of the dominant carnivores in its before the rise of more advanced theropod groups in the .

Discovery and nomenclature

History of discovery

The specimen of Yangchuanosaurus shangyouensis (CV 00215), consisting of a complete and nearly complete , was discovered in 1976 during construction work at the Shangyou Reservoir Dam site near Yongchuan in Province, . This find, from the Upper , marked one of the most complete theropod skeletons recovered in at the time. The specimen was formally named Yangchuanosaurus shangyouensis in 1978 by Dong Zhiming, Zhang Yihong, Li Xuanmin, and Zhou Shiwu in a description published in Ke Xue Tong Bao. The genus name honors the Yongchuan (Yangchuan) District, while the species name refers to the Shangyou Reservoir locality. Preparation and initial study of the fossils were conducted at the Museum of Natural History, which cataloged the material and housed it as a key exhibit. In the early 1980s, additional Yangchuanosaurus fossils were unearthed from the Upper in Province, expanding knowledge of the . Notably, specimen CV 00214, a partial lacking a from the Wujiaba locality near , was initially referred to as a new of Szechuanosaurus in a 1978 faunal list but was reassigned to Yangchuanosaurus in subsequent analyses by Dong and colleagues in 1983. Other partial skeletons from the same stratigraphic unit were also documented during this period, contributing to a better understanding of theropod diversity in the region. The Museum of again played a crucial role, protecting these specimens during a 1981 flood that threatened the institution's collections.

Etymology

The genus name Yangchuanosaurus is derived from "Yangchuan" (an older transliteration of Yongchuan, a district in Municipality, , near the type locality), combined with the Greek word sauros, meaning "lizard" or "reptile," thus translating to "Yangchuan lizard." The name reflects the standard paleontological convention of honoring discovery sites, particularly prevalent in Chinese dinosaur nomenclature during the late 1970s as the field reemerged from the disruptions of the (1966–1976). The Y. shangyouensis honors the Shangyou Reservoir (Shangyou meaning "upper right" in Chinese), where the skeleton was unearthed in 1976 during dam construction; the suffix -ensis is a Latin-derived indicator of locality, common in under the . The and were formally established in 1978 by Dong Zhiming and colleagues in a description published in Ke Xue Tong Bao, amid growing Sino-international collaborations that facilitated rapid documentation of Jurassic theropods from Province. Post-1978 literature has occasionally proposed corrections to the , such as rendering the locality as "Yongchuanosaurus" to align with modern , though the original Yangchuanosaurus remains the valid binomial per ICZN priority rules. No major alternative generic names have been upheld, reflecting the stability of the original designation in subsequent revisions.

Valid species and synonyms

The type species of Yangchuanosaurus is Y. shangyouensis, established by Dong et al. in 1978 based on specimen CV 00215, consisting of a nearly complete including the , collected from the Upper in Province, , dating to the Oxfordian stage of the (approximately 161.2–157.3 Ma). In 1983, Dong et al. described Y. magnus as a second species within the , with CV 00216 representing a larger individual ( length approximately 111 cm compared to 78 cm in the Y. shangyouensis ) from the same formation and stage; however, subsequent analyses have synonymized Y. magnus with Y. shangyouensis, attributing differences to ontogenetic variation and morphological overlap rather than distinct taxa. Two additional nominal species have been proposed but remain questionable: Y. ? hepingensis, named by Gao in 1992 based on partial skeletal remains (specimen ZDM 0024) from the Upper , was reassigned to Sinraptor hepingensis by and Zhao in 1993 due to shared derived features, and is now widely regarded as outside Yangchuanosaurus despite initial placement; similarly, Y. ? zigongensis, described by Gao in 1993 from a partial and postcranial elements (originally under Szechuanosaurus zigongensis, ZDM 9012), has been debated as a potential distinct , a growth variant of Y. shangyouensis, or even a owing to the fragmentary nature of the material. Specimen CV 00214, a partial postcranial from the Upper recovered in the early and initially referred to Szechuanosaurus, was reassigned to Yangchuanosaurus in later studies, either as part of the Y. shangyouensis hypodigm or supporting Y. zigongensis, thereby influencing interpretations of intraspecific variation and overall within the genus. Phylogenetic analyses as of 2024–2025 indicate a consensus toward monospecificity for Yangchuanosaurus (encompassing Y. shangyouensis and its synonyms), though some studies question this by highlighting subtle morphological and size-based distinctions that could support multiple valid species pending further specimens.

Description

Size and general build

Yangchuanosaurus was a robust, bipedal theropod dinosaur well-adapted for terrestrial predation, featuring powerful hindlimbs that supported efficient locomotion on two legs, reduced forelimbs, and an elongated tail that aided in balance and maneuverability. The type species, Y. shangyouensis, attained an estimated body length of 8–8.5 meters in its holotype specimen, based on measurements of the preserved skeleton including a skull approximately 82 cm long. Larger specimens of the species Y. magnus reached up to 10.8 meters in total length, establishing it as one of the larger theropods of the Late Jurassic in Asia. Weight estimates derived from volumetric models of complete or near-complete skeletons range from about 1 metric ton for smaller individuals to 3.4 metric tons for the largest, highlighting its substantial mass relative to contemporaries. Overall body proportions in Yangchuanosaurus closely resembled those of Allosaurus, with a similar elongated skull, deep chest, and pillar-like hindlimbs, though it exhibited regional endemism as an Asian representative of the metriacanthosaurid lineage.

Skull and dentition

The skull of Yangchuanosaurus shangyouensis is elongated and robust, measuring approximately 82 cm in length and 50 cm in height in the holotype specimen. A larger specimen of Y. magnus exhibits a skull up to 1.11 m long, indicating ontogenetic or individual variation in cranial size. The cranium features a prominent nasal ridge formed by fused nasals, contributing to its overall low and laterally oval profile. Key cranial features include large orbits positioned for enhanced , aiding in for predation, and two antorbital fenestrae—the primary one large and triangular, the secondary smaller and rectangular—that may have housed expanded olfactory structures for scent detection. The is robust with a deep elliptical depression, while the is deep and strong, supporting powerful mechanics. Dentition is and adapted for flesh-slicing, with laterally compressed, posteriorly curved crowns bearing serrations. adductor mechanics suggest a bite force of 3,000–6,000 N, comparable to other large theropods for subduing prey.

Postcranial

The postcranial of Yangchuanosaurus is well-represented by multiple specimens, providing insights into its axial and appendicular adapted for bipedal locomotion. The vertebral column varies slightly between species but generally consists of 9–10 , 13–14 dorsal vertebrae, 5 sacral vertebrae, and at least 35 caudal vertebrae. In Y. shangyouensis, the (CV 00215) preserves 10 with concave posterior articular surfaces and sloping ventral margins, 13 dorsal vertebrae, and 5 sacral vertebrae fused into a robust . The dorsal vertebrae feature moderately elongated neural spines, with a spine-to-centrum height ratio of approximately 2.5:1, forming a slight midline ridge along the back. In Y. magnus, the tail comprises over 40% of total body length for counterbalance during movement. The emphasizes powerful hindlimbs for propulsion and reduced forelimbs. Hindlimbs are robust, with the measuring up to 1.2 m in larger specimens of Y. magnus (CV 00216), exceeding the length and supporting efficient bipedal . The pes is tridactyl, with three weight-bearing toes ending in large, curved (up to 15 cm long) for traction and prey restraint. Forelimbs are comparatively short, at about 40% of length, but retain a functional manus with three digits bearing sickle-shaped unguals, the second digit claw reaching 20 cm in . The pelvic girdle and thoracic elements further underscore locomotor adaptations. The ilium is broad and elongate, with a length exceeding 1 m in large individuals, providing expansive attachment sites for strong musculature such as the iliofemoralis. The pubis and form a closed , with the pubis bearing a prominent boot-like expansion distally. include elongate dorsal ribs articulating with the vertebrae, and form a flexible of overlapping dermal bones supporting the ventral abdomen and aiding respiratory mechanics. Unique pathological features are evident in preserved specimens. Ribs in the Y. shangyouensis show evidence of healed fractures, with remodeling visible on mid-dorsal elements.

Classification

Taxonomic history

Yangchuanosaurus was first described and named by Dong Zhiming and colleagues in 1978 based on a nearly complete skeleton from the Upper Shangshaximiao Formation in Province, . The authors classified the new genus as a carnosaur within the broader group of theropod dinosaurs, explicitly comparing its morphology, , and overall build to that of the North American , emphasizing shared features such as a robust and serrated teeth suited for large prey. In the 1980s, further work by Dong and coauthors expanded the genus. They described Yangchuanosaurus magnus in 1983 as a second, larger based on a partial (CV 00216) from the same formation, distinguished by its greater size and proportionally massive with prominent crests. The same publication reassigned a partial postcranial (CV 00214) previously referred to other theropods to a new , Szechuanosaurus zigongensis, though this was interpreted as closely related to Yangchuanosaurus at the time. Subsequent analyses in the , such as Gao's 1992 description of additional material as Yangchuanosaurus hepingensis, reinforced the genus's recognition as a diverse group of large carnosaurs, but early suggestions of ontogenetic variation led to partial synonymy of some Y. magnus specimens with Y. shangyouensis, reducing the distinctiveness of certain traits. During the 2000s, taxonomic understanding advanced through phylogenetic studies. Carrano, Benson, and Sampson (2012) formally placed Yangchuanosaurus within , a family of basal allosauroids, in their comprehensive analysis of tetanuran relationships, recovering the as monophyletic based on shared postcranial features like elongated hindlimbs. However, this placement sparked debates on the monophyly of , as some character codings highlighted potential when incorporating Asian taxa. Recent analyses from 2019 onward have further refined the genus's taxonomy. Carrano et al. (2012) also reassigned Szechuanosaurus zigongensis to Yangchuanosaurus zigongensis, recognizing its affinities based on vertebral and limb morphology. Pol and Rauhut (2019), in a phylogenetic study incorporating new Jurassic theropod data, tentatively included material previously named Y. hepingensis (often referred to Sinraptor hepingensis since 1998) within Yangchuanosaurus while recovering Y. zigongensis as a more basal metriacanthosaurid outside the core genus, suggesting possible over-splitting in prior classifications and emphasizing the genus's position near the base of Allosauroidea. Rauhut et al. (2024), using a matrix modified from prior datasets, supported the monophyly of Metriacanthosauridae with Yangchuanosaurus positioned among derived members. Zou et al. (2025), describing the basal metriacanthosaurid Yuanmouraptor jinshajiangensis, recovered Yangchuanosaurus shangyouensis in a polytomy with Sinraptor species as more derived within the family, distinct from basal taxa like Yuanmouraptor and Xuanhanosaurus. Ongoing work through 2025 continues to explore these affinities, with some matrices indicating closer ties to early diverging theropod lineages.

Phylogenetic position

Yangchuanosaurus is positioned as a member of , a of basal allosauroid theropods, based on cladistic analyses of tetanuran phylogeny. In the comprehensive study by Carrano et al. (2012), which utilized a of 61 taxa and 295 characters, Yangchuanosaurus forms part of a monophyletic (also known as Sinraptoridae), nested within Allosauroidea and more closely related to Sinraptor and than to more derived allosauroids like or carcharodontosaurians. This placement highlights its role in the early diversification of large-bodied carnosaurs during the . Recent phylogenetic updates incorporating additional Asian specimens reinforce this positioning while refining internal relationships. For instance, Rauhut et al. (2024) analyzed theropod relationships using a modified matrix, recovering Yangchuanosaurus within a monophyletic alongside derived subclades including Metriacanthosaurinae (encompassing Sinraptor, , , and the newly described Alpkarakush). Similarly, Zou et al. (2025) placed Yangchuanosaurus shangyouensis in a derived with Sinraptor species within the family, distinct from basal metriacanthosaurids like Yuanmouraptor, underscoring its status among more advanced members. Key synapomorphies supporting , and thus Yangchuanosaurus's inclusion, include a relatively large promaxillary , a squamosal that forms a covering the quadrate head laterally, and a well-developed spinopostzygapophyseal lamina on the posterior vertebrae. These features, shared among East Asian and European members of the , distinguish it from other allosauroids and reflect adaptations for robust cranial and axial support in large predators. While the family's is consistently supported, some analyses show variability in the placement of basal taxa like Shidaisaurus, which may branch outside the Yangchuanosaurus-Metriacanthosaurinae , prompting ongoing refinement but no evidence of . No recent studies reassign Yangchuanosaurus to the stem of Carcharodontosauria, maintaining its basal allosauroid affinity.

Paleoecology

Geological context

The fossils of Yangchuanosaurus are primarily recovered from the Upper , located in the of . This stratigraphic unit dates to the Oxfordian stage, spanning approximately 161.2 to 157.3 million years ago, based on detrital U-Pb and biostratigraphic correlations from associated sedimentary layers. However, the age of the Upper remains debated, with some biostratigraphic analyses suggesting a (–) assignment for the upper member. The Upper represents a continental dominated by fluvial and lacustrine sediments, including purplish-red mudstones, sandy mudstones, siltstones, and interbedded sandstones. These deposits formed in a subtropical setting characterized by seasonal and a humid , indicative of a system with meandering rivers, deltaic influences, and shallow lakes. Taphonomic evidence suggests that Yangchuanosaurus specimens, often found as partially articulated skeletons, were preserved in fine-grained mudstones resulting from rapid within river channel or overbank deposits. The absence of marine fossils or confirms a fully terrestrial, non-marine depositional regime. Biostratigraphic correlation of the Upper with global stages relies on associated non-vertebrate fossils, including bivalves (e.g., Sichuanus spp.), ostracods, and charophytes, which align the unit with the Oxfordian and support its placement within the .

Associated fauna

The in Province, , preserves a diverse vertebrate assemblage from the Middle to Late Jurassic, contemporaneous with Yangchuanosaurus in the upper member, reflecting a complex in a fluvial-lacustrine environment. Herbivorous dinosaurs dominated the ecosystem, with large sauropods such as Mamenchisaurus—reaching lengths of up to 35 m—and Omeisaurus forming key components of the primary consumer base. Stegosaurs like Chungkingosaurus contributed to the herbivore diversity, occupying mid-sized niches among the vegetation. Other theropods coexisted with Yangchuanosaurus, including smaller coelophysoids and potential competitors such as Gasosaurus from the lower member, suggesting a tiered carnivore structure within the formation. Non-dinosaurian vertebrates enriched the assemblage, encompassing , crocodylomorphs, fishes, and amphibians, which occupied aquatic and semi-aquatic roles. Overall, the has yielded over 20 dinosaur taxa across its members, underscoring a rich, predator-prey balanced sustained by abundant plant resources and varied habitats.

Inferred biology and behavior

Yangchuanosaurus was a carnivorous , as evidenced by its blade-like teeth with fine serrations suited for slicing through flesh and its robust jaw musculature capable of exerting substantial bite forces to subdue large prey. These adaptations indicate it primarily hunted large herbivores, such as the sauropods and , that coexisted in its habitat, positioning it at the top of the . As a bipedal theropod, Yangchuanosaurus featured powerful hind limbs and a long, counterbalancing tail that facilitated agile locomotion, with biomechanical analyses of similar large allosauroids estimating top speeds of 20–30 km/h based on limb proportions and body mass around 2,000 kg. This speed range, derived from dynamic similarity models using Froude numbers, suggests it was capable of short bursts for predation rather than sustained pursuit, well-suited to navigating the forested floodplains of its environment. Growth in Yangchuanosaurus likely followed patterns observed in closely related allosauroids like , with rapid juvenile growth rates leading to skeletal maturity in 15–20 years, as inferred from bone histology showing annual growth lines and peak mass accretion of approximately 150 kg per year around age 15. Specimen size variations, including differences in proportions between known individuals, further support ontogenetic changes consistent with this accelerated developmental strategy typical of large theropods. Behavioral inferences for Yangchuanosaurus draw from pathological evidence in related large theropods, where frequent healed injuries—such as and fractures on bones—indicate an active, combative involving predation and intraspecific , possibly suggesting solitary or loose associations in small groups. Trackway assemblages from contemporaneous theropod sites, including those attributed to allosauroids, show parallel footprints implying gregarious movement, which may extend to Yangchuanosaurus for coordinated ambush tactics against large prey like sauropods.

References

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