Yunnanosaurus

*Yunnanosaurus huangi*

**Yunnanosaurus** (Lizard from Yunnan) was a prosauropod dinosaur closely related to Lufengosaurus. It was one of the last prosauropods, living into the Middle Jurassic. Its skeleton was found in Yunnan, China with Dilophosaurus.

Yunnanosaurus is a genus of prosauropod dinosaur from the Early to Middle Jurassic Period, a position in time that makes it one of the last prosauropods. It is closely related to Lufengosaurus. Known from two valid species, Yunnanosaurus ranged in size from 7 meters (23 feet) long and 2 meters (7 feet) high to 13 meters (42 feet) long in the largest species.

## Discovery

Yang Zhongjian (aka C. C. Young) discovered the first Yunnanosaurus skeletons in the Lufeng Formation of Yunnan, China. The fossil find was composed over twenty incomplete skeletons, including two skulls, and were excavated by Tsun Yi Wang.

In 2007, Lu and colleagues described another species of Yunnanosaurus, Y. youngi (named in honor of C. C. Young). In addition to various skeletal differences, at 13 meters (42 feet) long Y. youngi was significantly larger than Y. huangi (which reached only 7 meters 23 feet), and Y. youngi is found later in the fossil record, hailing from the Middle Jurassic, which would make it latest surviving "prosauropod". The holotype specimen CXMVZA 185 consists of ten cervical vertebrae, fourteen dorsal vertebrae, three fused sacral vertebrae, seventeen caudal vertebrae, both pubic bones, both ischia, and the right illium. The skull of this species is not known.

## Description

### Dentition

There were more than sixty spoon shaped teeth in the jaws of Yunnanosaurus, and were unique among prosauropods in that its teeth were self-sharpening because they “[wore] against each other as the animal fed.” Scientists consider these teeth to be advanced compared to other prosauropods, as they share features with the sauropods.

However, scientists do not consider Yunnanosaurus to be especially close to the sauropods in phylogeny because the remaining portions of the animals body are distinctly prosauropod in design. This critical difference implies that the similarity in dentition between Yunnanosaurus and sauropods might be an example of convergent evolution.

## Classification

The type species, Y. huangi, was named by C. C. Young in 1942, and he erected the family Yunnanosauridae to contain it, though the family currently comprises only this genus. Young also named a second species, Y. robustus, in 1951, but this has since been included in the type species. The confusion in classification arose due to that the earliest specimens were of juveniles while the “Y. robustus” specimens represented fully grown adults.

## Paleoecology

The type specimens of Yunnanosaurus huangi and Yunnanosaurus robustus were recovered in the Huangchiatien (Dahungtien) locality of the Lufeng Formation in Yunnan, China. The Y. huangi holotype specimen IVPP V20 and the Y. robustus holotype specimen IVPP V93, were collected by Chung Chien Young in terrestrial sediments from the upper dark/deep red beds of the Zhangjiawa Member of this formation, that are believed to have been deposited during the Sinemurian stage of the Jurassic period, approximately 199 to 190 million years ago. Several other specimens assigned to Y. huangi (IVPP V54, IVPP V47, IVPP V61, IVPP V62, IVPP V63, IVPP V96, IVPP V264), and Y. robustus (IVPP V39, IVPP V94) were also recovered by Young in this locality. These specimens are all housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology, in Beijing, China. In the years to come several more specimens assigned to these two species were recovered from Zhangjiawa Member of this formation.
Chung Chien Young had also explored the lower dark/dull purple beds of the Shawan Member of the Lufeng Formation and found more specimens that he later assigned to Y. huangi. Specimen IVPP V32 was collected by Young in 1938 in dark red, argillaceous sandstone that is believed to have been deposited during the Hettangian stage of the Jurassic period, approximately 201 to 199 million years ago. Specimens IVPP V57, IVPP V60 and IVPP V272 were collected by Young in blue mudstone from the same formation and were also assigned to Y. huangi. These specimens from the Shawan Member are also housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology.
Yunnanosaurus huangi and Yunnanosaurus robustus shared their paleoenvironment with the ornithischians Bienosaurus, and Tatisaurus, the sauropodomorphs Gyposaurus, Lufengosaurus, and Jingshanosaurus, and the theropods Sinosaurus triassicus and Eshanosaurus.

## JPInstitute.com Description

Yunnanosaurus was one of the first large plant-eaters in Asia. This dinosaur was a prosauropod, which means it was an ancestor of the long-necked plant-eating giants that came later in the Jurassic Period. It would have been able to walk on its back legs and stand up to reach the leaves higher in the trees. However, it was big enough that it would have also walked on all four legs.

Yunnanosaurus is considered a close relative of Lufengosaurus, with some differences in the skull. There are two recognized species of this genus.

## Links

https://web.archive.org/web/20030813055255/http://www.jpinstitute.com/dinopedia/dinocards/dc\_yunna.html