''Xuanhanosaurus'' (meaning "

Xuanhan Xuanhan County () is a county in the northeast of Sichuan, Sichuan Province, China, bordering Chongqing to the east. It is under the administration of the prefecture-level city of Dazhou. According to recent population census, Xuanhan county ha ...

lizard") is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

that lived during the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

(

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

) of the

Sichuan Basin The Sichuan Basin (), formerly transliterated as the Szechwan Basin, sometimes called the Red Basin, is a lowland region in southwestern China. It is surrounded by mountains on all sides and is drained by the upper Yangtze River and its tributar ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

, around 166 million years ago. This taxon represents one of the various non-

coelurosaurian Coelurosauria (; from Greek, meaning "hollow-tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyra ...

tetanuran Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, and coelurosaurs (which includes tyrannosauroids, ornithomimosaurs, compsognathids and maniraptoran ...

taxa found on the Middle Jurassic of the region, uncovered in the

Lower Shaximiao Formation The Shaximiao Formation () is a Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in and around the ...

. Although it has been known for more than 40 years, this taxon has been the subject of very few studies, although most seem to agree that it is a tetanuran, possibly a basal

allosauroid Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...

, highlighting the fact that it has a

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

fourth

metacarpal In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones ( wrist bones), which articulate ...

Discovery

The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''Xuanhanosaurus qilixiaensis'' was named by

Dong Zhiming Dong Zhiming (Chinese language, Chinese: 董枝明, Pinyin: ''Dǒng Zhimíng''; January 1937 – 20 October 2024) was a Chinese vertebrate paleontologist formerly employed at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) ...

in 1984. The generic name refers to

Xuanhan County Xuanhan County () is a county in the northeast of Sichuan, Sichuan Province, China, bordering Chongqing to the east. It is under the administration of the prefecture-level city of Dazhou. According to recent population census, Xuanhan county ha ...

Sichuan Sichuan is a province in Southwestern China, occupying the Sichuan Basin and Tibetan Plateau—between the Jinsha River to the west, the Daba Mountains to the north, and the Yunnan–Guizhou Plateau to the south. Its capital city is Cheng ...

, while the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

is derived from the town of Qilixia. The specimen was recovered in 1979, when the author was conducting a Dinosaurian Fossil survey in Sichuan Province, when was guided by Liu Yawen and the 137th team to examine the Qilixia section, where they recovered the holotype of this new taxon at the southern flank of the Qili Dorsal Slope. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen, IVPP V.6729, was found in

. It consists of a partial skeleton without a skull, namely a scapula missing the posterior end, coracoid, a possible sternum humerus, radius, ulna, manus, as well a few fragmentary dorsal vertebrae.

Description

Xuanhanosaurus qilixiaensis size comparison

''Xuanhanosaurus'', originally thought to be around 6 m long, was approximately 4.8 meters (16 ft) in length, with a weight of 265

kilogram The kilogram (also spelled kilogramme) is the base unit of mass in the International System of Units (SI), equal to one thousand grams. It has the unit symbol kg. The word "kilogram" is formed from the combination of the metric prefix kilo- (m ...

s (585 lb). ''Xuanhanosaurus'' had powerful forelimbs, over 65 cm long; this, along with the retention of the fourth metacarpal in the hand, led Dong to suggest that ''Xuanhanosaurus'' might have walked on all four legs. If so, it would be the only known four-legged meat-eater among dinosaurs. Later paleontologists have not agreed with Dong's original assessment. They think this dinosaur walked on its hind legs as other theropods did,

pronation Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

of the lower arm being impossible. The strong arms could instead have been useful in catching prey. The retention of the 4th metarcarpal is the most notorious feature of this taxon, yet the presence of a convex proximal surface on the distal carpal 2 has been used to arge it represents a second stage in the evolution of the "semilunate" carpal. Some recent work have notified that beyond the 4th metarcarpal, ''Xuanhanosaurus'' also retains ceratosaurian-like short phalanges II-1, similar in length to the ones recovered on ''

Saltriovenator ''Saltriovenator'' (meaning " Saltrio hunter") is a genus of ceratosaurian dinosaur that lived during the Sinemurian stage of the Early Jurassic in what is now Italy. The type and only species is ''Saltriovenator zanellai''; in the past, the sp ...

''. The scapula was found to be bulkier than in ''

Allosaurus ''Allosaurus'' ( ) is an extinct genus of theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic period ( Kimmeridgian to late Tithonian ages). The first fossil remains that could definitively be ascribed to th ...

''. The distal humerus is enlarged laterally, forming a one-inch step. The vertebrae are posteriorly concave and anteriorly protruding, with cervical centra having flat anterior articular surfaces, also seen in '' Condorraptor'', ''

Piatnitzkysaurus ''Piatnitzkysaurus'' ( ; meaning "Piatnitzky's lizard") is a genus of tetanuran theropod dinosaur that lived approximately 179 to 177 million years ago during the lower part of the Jurassic Period in what is now Argentina. ''Piatnitzkysaurus'' wa ...

'' and ''"

Szechuanosaurus ''Szechuanosaurus'' (" Szechuan lizard") is an extinct genus of carnivorous theropod dinosaur from the Late Jurassic. Fossils referred to the genus have been found in China, Asia in the Oxfordian-?Tithonian (Peng ''et al''., 2005). Its type spec ...

" zigongensis'', yet lacking posterior pneumatic foramen or fossa, which is seen on the first 2 genera.

Phylogeny

Originally, ''Xuanhanosaurus'' was assigned by Dong to the

Megalosauridae Megalosauridae is a monophyletic Family (taxonomy), family of Carnivore, carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dino ...

, when this group was meant to include a larger amount of taxa, and was argued to be in the middle stage of the evolution of the Tetanurae due to its vestigial fourth metacarpals. Latter it was found by Roger Benson in 2009 to belong to a primitive lineage of the

Megalosauroidea Megalosauroidea (meaning 'great/big lizard forms') is a superfamily (or clade) of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as '' Megalosaurus bucklandii'' and all taxa ...

. A more recent study by Benson and colleagues in 2010 found that it was more likely to be the most primitive known member of the

Metriacanthosauridae Metriacanthosauridae (Greek for "moderately-spined lizards") is an extinct family of allosauroid theropod dinosaurs that lived in Europe and Asia from the Middle Jurassic to the Early Cretaceous. The family is split into two subgroups: Metriacan ...

family.Supporting Information
/ref> In 2018, based on several conditions such as the length and retention of the vestigial 4th metacarpal, it was argued that this taxon and ''"

" zigongensis'' belong to early-diverging branches of the ceratosaurian-tetanuran node. In 2019, Rauhut and Pol recovered ''Xuanhanosaurus'' outside of Metriacanthosauridae, as the basalmost member of

Allosauroidea Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...

References

Carnosauria Dinosaur genera Bathonian dinosaurs Shaximiao Formation Dinosaurs of China Fossil taxa described in 1984 Taxa named by Dong Zhiming {{theropod-stub