''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 ...
of
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 ...
of
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 ...
in
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
Qilixia is a town in Shaanxi, 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
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
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 ...
's
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'' 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 languages, Germanic origin, derived from the elements ', ''χrōþi'' ("fame", "renown", " ...
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 sha ...
.
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 sub ...
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