| Tonganosaurus | |
|---|---|
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Family: | †Mamenchisauridae |
| Genus: | †Tonganosaurus Liet al.,2010 |
| Species: | †T. hei |
| Binomial name | |
| †Tonganosaurus hei Liet al., 2010 | |
Tonganosaurus (named for the town ofTong'an, Sichuan where it was found) is agenus ofmamenchisauridsauropoddinosaur, similar toOmeisaurus. 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 theYimen Formation,China.[1] The horizon of the specimen and the age of the Yimen Formation is controversial. The formation has been divided into three levels, andTonganosaurus appears to be of late Early Jurassic (Pliensbachian) in age.[2]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 in2010, and thetype species isTonganosaurus hei.[3]
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 ofTonganosaurus has been calculated in size, usingOmeisaurus as reference, at 11.6 metres (38 ft) long. In life, it was probably a little bigger, about 12 metres (39 ft).[3]
In 2007, theChengdu University of Technology Museum based on information gathered from citizen scientists, searched for dinosaurs inTongan Town,Huili County,Sichuan Province. They found the fossils ofTonganosaurus 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 familyMamenchisauridae implies a high diversity of sauropods in the late Early Jurassic. The specimen was kept at Chengdu University of Technology Museum, with the numberMCDUT 14454.[3]
Tonganosaurus holotype comes from the Upper section of theYimen Formation, being associated withBrontopodus tracks with also Mamenchisaurid resemblance, that maybe were made by this taxon.[4] These layers are also filled withOstracodans (Darwinula),Stoneworts,Bivalves (Utschamiella andSibireconcha) andConchostracans.[5] The Stonewort assemblage is dominated by the genusAclistochara (A. nuguishanensis,A. yunnanensis) associated with elements ofPorochara and sporadic individuals ofStenochara, suggesting shallow-deep lake and flood environments.[6] Apart fromTonganosaurus, Sauropodomorph remains where uncovered, likely similar toYunnanosaurus of the same age.[7]
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