The Qingtoushan Formation is a Middle

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

-age geologic formation in the

Qilian Mountains The Qilian Mountains (), together with the Altyn-Tagh sometimes known as the Nan Shan, as it is to the south of the Hexi Corridor, is a northern outlier of the Kunlun Mountains, forming the border between Qinghai and the Gansu provinces of n ...

Gansu Gansu is a provinces of China, province in Northwestern China. Its capital and largest city is Lanzhou, in the southeastern part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibetan Plateau, Ti ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. It is known for its diverse tetrapod fauna known as the Dashankou fauna, which likely dates to the

Roadian In the geologic timescale, the Roadian is an age or stage of the Permian. It is the earliest or lower of three subdivisions of the Guadalupian Epoch or Series. The Roadian lasted between and million years ago (Ma). It was preceded by the Kun ...

, and includes some of the oldest known therapsids. This formation was previously erroneously named as the Xidagou Formation, a name which applies to otherwise

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

strata in the northern Qillian Mountains. The formation is over 300 metres thick, and primarily consists of purple-red coarse

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s, with minor purple

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

.Liu J, Qinghua S, Keqin S, Lu L (2012
The horizon of Dashankou Fauna and the Permo-Triassic strata in northern Qilian area, China
Vertebr Palasiat 50(4):373–381 (In Chinese)

Paleobiota

Synapsida

Sauropsida

Chronisuchia

Temnospondyli

References