Öösh Formation

The Öösh Formation, also known as the Tevsh Formation is a geological formation of Lower Cretaceous strata in Övörkhangai Province, Mongolia. Dinosaur remains are among the fossils that have been recovered from the formation.^[1] It overlies folded and metamorphosed basement strata of the Gobi region, and is capped by basalt. The succession is around 600 metres thick and consists of red claystones and sandstones, along with black thinly laminated shales. The claystones and sandstones were deposited as part of an alluvial fan system, while the shales were deposited in lakes present in the foot of the fan.^[2] Many of the fossils come from the "Cannonball beds", which comprise the lowest 60 metres of the unit and consist of green siltstone.^[2]

Öösh Formation
Stratigraphic range: Berriasian-Barremian ~141–125 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Sub-units	Cannonball beds
Underlies	Basalt
Overlies	Basement
Thickness	600 m (2,000 ft)
Lithology
Primary	Sandstone, claystone, shale
Other	Siltstone
Location
Coordinates	44.2°N 102.7°E / 44.2; 102.7
Approximate paleocoordinates	45.0°N 103.3°E / 45.0; 103.3
Region	Ovorkhangai
Country	Mongolia
Öösh Formation (Mongolia)

Vertebrate paleofauna

Dinosaurs

Dinosaurs of the Öösh Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Asiatosaurus	A. mongoliensis			Teeth	Indeterminate sauropod
Halszkaraptorinae indet.[3]				ISMD-VP09, preserving a maxillary fragment, two teeth, and partial appendicular elements	Halszkaraptorine[4]
Prodeinodon	P. mongoliensis			Several teeth, fragmentary tibia, fragmentary fibula	Indeterminate theropod
Protiguanodon	P. mongoliensis				Reclassified as a species of Psittacosaurus, Psittacosaurus protiguanodonensis
Psittacosaurus	P. mongoliensis					Psittacosaurus fossil from the Hühteeg Svita with gastroliths in its stomach region, American Museum of Natural History
	P. protiguanodonensis				Junior synonym of P. mongoliensis
Shanag[5]	S. ashile[5]			Upper and lower jaw fragment (IGM 100/1119)	A paravian, possibly a dromaeosaur

Mammals

Mammals of the Öösh Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Gobiconodon[6]	G. hopsoni[6]		Cannonball Member of Öösh Formation, possibly equivalent of Tevsh Formation	Two upper and lower jaws (PSS-MAE 140 (Holotype) & PSS-MAE 139)

Pterosaurs

Pterosaurs of the Öösh Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Indeterminate tapejaroid[2][7]				"Single cervical vertebra (IGM 100/1321)"[2]

Squamates

Squamates of the Öösh Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Norellius[8]	N. nyctisaurops			"Nearly complete skull with mandibles and partial hyoid"	Gekkonomorph

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

See also

• List of dinosaur-bearing rock formations