''Xuanhanosaurus'' (meaning "

Xuanhan Xuanhan County () is a county in the northeast of 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 has a popul ...

lizard") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

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

that lived during the Middle

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

, around 167.7 to 161.2 million years ago.

Discovery

The

type species In 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 species that contains the biological type specimen ...

''Xuanhanosaurus qilixiaensis'' was named by

Dong Zhiming Dong Zhiming (Chinese: 董枝明, Pinyin: ''Dǒng Zhimíng''; born January 1937) is a Chinese vertebrate paleontologist formerly employed at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing. He began working at the ...

in 1984. The generic name refers to

Xuanhan County Xuanhan County () is a county in the northeast of 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 has a popul ...

Sichuan Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestant missions) is a province in Southwest China occupying most of the ...

, while the specific name is derived from the town of Qilixia. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen, IVPP V.6729, was found in

Lower Shaximiao Formation The Shaximiao Formation () is a Middle Jurassic, 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 ...

. It consists of a partial skeleton without a skull.Dong, Z. (1984). "A new theropod dinosaur from the Middle Jurassic of Sichuan Basin". ''Vertebrata PalAsiatica'' 22(3):213-218

Description

Xuanhanosaurus qilixiaensis size comparison

''Xuanhanosaurus'' was approximately 4.5 meters (15 ft) in length, with a weight of 250

kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially ...

s (550 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 terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

of the lower arm being impossible. The strong arms could instead have been useful in catching prey.

Phylogeny

Assigned by Dong to the

Megalosauridae Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dinosaurs. They were a relatively ...

, ''Xuanhanosaurus'' was found by

Roger Benson Roger is a given name, usually masculine, and a surname. The given name is derived from the Old French personal names ' and '. These names are of Germanic origin, derived from the elements ', ''χrōþi'' ("fame", "renown", "honour") and ', ' ( ...

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 s ...

. 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 is an extinct family of allosauroid theropod dinosaurs that lived from the Middle Jurassic to the Early Cretaceous. When broken down into its Greek roots, it means "moderately-spined lizards". The family is split into two su ...

family.Supporting Information
/ref> In 2019, Rauhut and Pol recovered ''Xuanhanosaurus'' outside of Metriacanthosauridae, as the basalmost member of

Allosauroidea Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four family (biology), families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroid ...

References

Metriacanthosaurids Middle Jurassic dinosaurs of Asia Jurassic China Taxa named by Dong Zhiming Fossil taxa described in 1984 Paleontology in Sichuan {{theropod-stub