''Tonganosaurus'' (named for the town of Tong'an, Sichuan where it was found) 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 ...

mamenchisaurid Mamenchisauridae is a family of sauropod dinosaurs belonging to Eusauropoda known from the Jurassic and Early Cretaceous of Asia and Africa. Some members of the group reached gigantic sizes, amongst the largest of all sauropods. Classification T ...

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

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 ...

, similar to ''

Omeisaurus ''Omeisaurus'' (meaning "Omei lizard") is a genus of sauropod dinosaur from the Middle Jurassic Period (Bathonian-Callovian stage) of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation of ...

''. It is known from one specimen consisting of twenty vertebrae, a front limb and pectoral girdle, and a complete hind limb with partial hip. It was discovered in the Yimen Formation,

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 ...

. The horizon of the specimen and the age of the Yimen Formation is controversial. The formation has been divided into three levels, and ''Tonganosaurus'' appears to be of late Early Jurassic (

Pliensbachian The Pliensbachian is an age of the geologic timescale and stage in the stratigraphic column. It is part of the Early or Lower Jurassic Epoch or Series and spans the time between 190.8 ± 1.5 Ma and 182.7 ± 1.5 Ma (million years ago). The Plien ...

) age. ''Tonganosaurus'' is the oldest known member of the mamenchisaurids, being almost 15 million years older than the next-oldest members of the group. It was first named by Li Kui, Yang Chun-Yan, Liu Jian and Wang Zheng-Xin in

2010 File:2010 Events Collage New.png, From top left, clockwise: The 2010 Chile earthquake was one of the strongest recorded in history; The Eruption of Eyjafjallajökull in Iceland disrupts air travel in Europe; A scene from the opening ceremony of ...

and 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 ...

is ''Tonganosaurus hei''.

Description

The ratio of the front and rear limbs is 0.80. The tibia was straight and thick, with a length 75% that of the femur. The holotype is an incomplete skeleton of an adult sauropod. The skeleton of ''Tonganosaurus'' has been calculated in size, using ''

'' as reference, at long. In life, it was probably a little bigger, about .

History of discovery

In 2007, the

Chengdu University of Technology Museum Chengdu (, ; simplified Chinese: 成都; pinyin: ''Chéngdū''; Sichuanese pronunciation: , Standard Chinese pronunciation: ), alternatively romanized as Chengtu, is a sub-provincial city which serves as the capital of the Chinese province ...

based on information gathered from citizen scientists, searched for dinosaurs in Tongan Town,

Huili County Huili (; Yi: or ''nyi ddix xiep'' or ''hop li xiep'') is a county-level city of far southern Sichuan province, China. It is under the administration of the Liangshan Yi Autonomous Prefecture. The county-level city was severely affected by t ...

Sichuan Province 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 ...

. They found the fossils of ''Tonganosaurus'' in the middle of the lower part of the Yimen Formation, whose age is estimated on 184.5 Ma. The fossils included about 20 vertebrae, a complete right shoulder blade and right forelimb, a distal left humerus, intact left and right ischia, a left femur, and complete right hind limb, and more than 10 scattered cervical vertebrae, ribs, tibia and claw bones. The fossils were collected in the same general area and were proportional, so they were believed to belong to the same animal. Being the first representative of the family

Mamenchisauridae Mamenchisauridae is a family of sauropod dinosaurs belonging to Eusauropoda known from the Jurassic and Early Cretaceous of Asia and Africa. Some members of the group reached gigantic sizes, amongst the largest of all sauropods. Classification T ...

implies a high diversity of sauropods in the late Early Jurassic. The specimen was kept at Chengdu University of Technology Museum, with the number MCDUT 14454.

Paleoenvironment

''Tonganosaurus'' holotype comes from the Upper section of the Yimen Formation, being associated with ''

Brontopodus ''Brontopodus'' is an ichnogenus of dinosaur footprint. The footprint has diplodocid form, but four toes when almost every diplodocid has no more than three. This leaves '' Dyslocosaurus'' as the only known genus capable of producing the footpri ...

'' tracks with also Mamenchisaurid resemblance, that maybe where make by this taxon. This layers are also filled with

Ostracoda Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...

ns (''

Darwinula ''Darwinula'' is a genus of ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several ...

''),

Stonewort Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Depending on the treatment of the genus ''Nitellopsis'', living (extant) species are placed into either one family ( Ch ...

Bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s ('' Utschamiella'' and '' Sibireconcha'') and

Conchostraca Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classifi ...

ns. The Stonewort assemblage is dominated by the genus '' Aclistochara'' (''A. nuguishanensis'', ''A. yunnanensis'') associated with elements of '' Porochara'' and sporadic individuals of '' Stenochara'', suggesting shallow-deep lake and flood environments. Apart from ''Tonganosaurus'', Sauropodomorph remains where uncovered, likely similar to ''

Yunnanosaurus ''Yunnanosaurus'' ( ) is an extinct genus of sauropodomorph dinosaur that lived approximately 199 to 183 million years ago in what is now the Yunnan Province, in China, for which it was named. ''Yunnanosaurus'' was a large sized, moderately-buil ...

'' of the same age.

References

Mamenchisaurids Early Jurassic dinosaurs of Asia Fossil taxa described in 2010 Paleontology in Sichuan {{Sauropodomorph-stub