The Xintiangou Formation is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

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 ...

. Part of the stratigraphy of the

Sichuan Basin The Sichuan Basin (), formerly transliterated as the Szechwan Basin, sometimes called the Red Basin, is a lowland region in southwestern China. It is surrounded by mountains on all sides and is drained by the upper Yangtze River and its tributa ...

, it is of an uncertain

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

age, with preliminary U-Pb estimates giving an age range of 170 ma. It predominantly consists of interbedded mudstone and sandstone, with subordinate shelly limestone. At the Laojun site remains of

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...

, freshwater sharks,

temnospondyls Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...

, sauropterygians,

crocodyliformes Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...

, the

Xinjiangchelyid Xinjiangchelyidae is an extinct family of turtles known from the Lower Jurassic to the Middle Cretaceous of Asia and western Europe. They have generally been interpreted as either being basal cryptodires or placed outside of crown Testudines. Ge ...

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

'' Protoxinjiangchelys'' and

tritylodontids Tritylodontidae ("three-knob teeth", named after the shape of their cheek teeth) is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, bearing several mammalian traits like erect limbs, endothermy and details ...

are known. The dinosaurs ''

Sanxiasaurus ''Sanxiasaurus'' (meaning "Sanxia lizard", after the Three Gorges, Chinese ''Sanxia'', of the Yangtze River) is a genus of neornithischian dinosaur from the Middle Jurassic Xintiangou Formation in the Chongqing Municipality of China. The type ...

,'' ''

Yunyangosaurus ''Yunyangosaurus'' (meaning "Yunyang County lizard") is a genus of possible megalosauroid dinosaur from the Xintiangou Formation in Chongqing, China China, officially the People's Republic of China (PRC), is a country in East Asia. It i ...

'', and indeterminate sauropods are also known from the formation. Theropod and ornithopod tracks have also been reported from the formation.

References

{{reflist Jurassic System of Asia Jurassic China Toarcian Stage Aalenian Stage