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 251.9 Mya. It is the last ...

-age geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

in the

Qilian Mountains The Qilian Mountains (, also romanized as Tsilien; Mongghul: Chileb), together with the Altyn-Tagh (Altun Shan) also known as Nan Shan (, literally "Southern Mountains"), as it is to the south of Hexi Corridor, is a northern outlier of the Kunlu ...

of Gansu, China. 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 ...

, and includes some of the oldest known

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

s. This formation was previously erroneously named as the Xidagou Formation, a name which applies to otherwise

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

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 sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, with minor purple mudstone.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