Sao Khua Formation

The Sao Khua Formation (Thai: หมวดหินเสาขัว) is a middle member of the Khorat Group. It consists of an alteration of pale red to yellowish-gray, fine to medium-grained sandstone and grayish-reddish brown siltstone and clay. Rare pale red to light gray conglomerates, containing carbonate pebbles, are also characteristic of this formation. This geological formation in Thailand dates to the Early Cretaceous age, specifically the Valanginian through Hauterivian stages.^[1]

Sao Khua Formation
Stratigraphic range: late Valanginian-early Hauterivian ~133.6–132.1 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Restoration of Siamosaurus, Sunosuchus and Phuwiangosaurus in the Sao Khua Formation palaeoenvironment.
Type	Geological formation
Unit of	Khorat Group
Underlies	Phu Phan Formation
Overlies	Phra Wihan Formation
Thickness	~120 m (390 ft)
Lithology
Primary	Sandstone, conglomerate
Other	Siltstone, claystone
Location
Coordinates	16.7°N 102.3°E / 16.7; 102.3
Approximate paleocoordinates	14.3°N 112.4°E / 14.3; 112.4
Region	Indochina
Country	Thailand
Extent	Khorat Plateau
Type section
Named by	Ward & Bunnag
Year defined	1964
Sao Khua Formation (Thailand)

Dinosaur remains are among the fossils that have been recovered from the formation.^[2]

Depositional environment

Based on paleosols and lithostratigraphy, the Sao Khua Formation is believed to have been deposited in a warm to slightly cool semi-arid climate by a meandering river system.^{[citation needed]} Geochemistry is indicative of a stable humid subtropical climate regime, and sedimentation is thought to have occurred in a floodplain setting which was fed by bedload-rich large meandering channels.^[1] Paleocurrent analysis suggests the sand channels at the time of deposition of the formation probably formed a braided channel environment.^[3]

Fossil content

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.

Amphibians

Amphibians reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Anura indet.	Indeterminate	Nong Bua Lamphu province.[4]	Humeri (SHM-PT 529 and SHM-PT 530) and a pelvic girdle (SHM-HY 231).[4]	A frog.

Reptiles

Dinosaurs

Dinosaurs reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Brachiosauridae	Indeterminate	Phu Wat B Locality, Phu Kao Mountain range	A tooth.[5]	Similar to other brachiosaurid teeth.
Carcharodontosauridae	Indeterminate	Locality Phu Wiang 1a, Khon Kaen province.[6]	"Fragment of the posterior part of a right maxilla".[6]	A carcharodontosaur.
Compsognathidae?	Indeterminate		[6][7][8]	A very small theropod form.[6][7]
Diplodocoidea	Indeterminate
Kinnareemimus	K. khonkaenensis	Locality Phu Wiang 5, Phu Wiang district, Khon Kaen province.[9]	Vertebral, pelvic and limb elements.[9]	An ornithomimosaur.
Ornithurae?		Khok Kong, Kalasin province.[10]	A humerus fragment.[10]	May represent an early ornithurine, and probably is not an enantiornithine.
Phuwiangosaurus	P. sirindhornae	Khon Kaen province.[11] Nong Bua Lamphu Province.[5]	"Partial skeletons, juvenile - adult", & 2 additional vertebrae.[11][12] A scapula and a partial skeleton have also been referred.[5]	A titanosaur.
Phuwiang spinosaurid B	Indeterminate	PW9 ‘Hin Lad Yao’ locality site A and site B, Phu Wiang district, Khon Kaen province.[13]	Caudal vertebrae.[13]	A spinosaur.
Phuwiangvenator	P. yaemniyomi	Phu Wiang Site 9B, Phu Wiang Mountain, Khon Kaen province.[14]		A megaraptoran.
Siamosaurus	S. suteethorni		Isolated teeth.[15][16]	A potentially dubious spinosaur.
Siamotyrannus	S. isanensis		"Pelvis, dorsal, sacral, and caudal vertebrae."[17][18]	An avetheropodan of uncertain position
Vayuraptor	V. nongbualamphuensis	Phu Wat Site A1 Locality, Nong Sang, Nong Bua Lamphu province.[14]		A megaraptoran.

• Sauropoda indet. 1 and 2

Lizards

Lizards reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Anguimorpha indet.		Phu Phok (SK1), Sakhon Nakhorn Province.[19]	Fossilized eggs containing embryos.[19]	Eggs originally thought to be of theropods like Epidendrosaurus.[20]

Pseudosuchians

Pseudosuchians reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Goniopholis	G. phuwiangensis	Phu Wiang district.[21]	A dentary.[21][22]	Reassigned to Sunosuchus.
Siamosuchus	S. phuphokensis	Phu Phok, Kok Prasil Sub-district, Phu Phan district, Sakon Nakhon province.[23]	A partly articulated skeleton (PPC-1).[23]	A goniopholidid.
Sunosuchus	S. phuwiangensis	Phu Wiang district.[21]	A dentary.[22]	Originally reported as Goniopholis phuwiangensis.
Theriosuchus	T. grandinaris	Phu Phok, Kok Prasil Sub-district, Phu Phan district, Sakon Nakhon province.[24]	"PPC-2, a nearly complete rostrum and dentary".[24]	An atoposaurid.
Varanosuchus	V. sakonnakhonensis	Phu Sung locality near Mueang Sakon Nakhon district, Sakon Nakhon province.[25]	A nearly complete skull and skeleton (SM-2021-1-97/101), a nearly complete skull (SM-2023-1-16), and a partial skull table (SM-2023-1-17).[25]	An atoposaurid.

Pterosaurs

Pterosaurs reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Ornithocheiridae		Phu Phok, Sakon Nakhon province.[26]	An isolated tooth crown (SMP25).[26]	Most comparable to ornithocheirid teeth from the Cambridge Greensand and Kem Kem beds.[26]

Turtles

Turtles reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Isanemys	I. srisuki	Kalasin, Khon Kaen and Sakon Nakhon provinces.[27]	Over 20 shells & additional isolated shell plates.[27]	An adocid.
Kizylkumemys	K. sp.	Khon Kaen, Kalasin and Nong Bua Lamphu provinces.[27]	Abundant but very fragmentary shell plates.[27]	A carettochelyid.
Protoshachemys	P. rubra	Phu Din Daeng, Nakhon Phanom province.[28]	Shell material.[28]	An adocid.

Fish

Bony fish

Bony fish reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Siamamia	S. naga	Phu Phok.[29]		A bowfin.

Cartilaginous fish

Cartilaginous fish reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Heteroptychodus	H. steinmanni		Over 130 fragmentary teeth.[30]	A hybodont
Hybodontiformes	Incertae sedis		2 dermal denticles and a cephalic spines.[30]	Indeterminate hybodontiform remains
Hybodus	"H." sp. A		18 fragmentary crowns.[30]	A hybodontid
	H. sp. B		Over 170 incomplete teeth.[30]	A hybodontid
Isanodus	I. paladeji	Phu Phan Thong, Nong Bua Lamphu province.[30]	185 incomplete teeth.[30]	A hybodont
Lonchidion	L. khoratensis	Phu Phan Thong, Nong Bua Lamphu province.[30]	25 teeth.[30]	A hybodont
Mukdahanodus	M. trisivakulii	Nong Sung district, Mukdahan province.[30]	11 isolated crowns.[30]	A hybodont
Parvodus	P. sp.		19 teeth.[30]	A hybodont
Sclerorhynchidae		Base of Phu Kum Khao hill in Sahatsakhan, Kalasin province.[31]	A rostral tooth (SM2012-1-021).[31]	A sawskate

Invertebrates

Bivalves

Bivalves reported from the Sao Khua Formation
Genus	Species	Presence	Material	Notes	Images
Pseudohyria	P. (Matsumotoina) somanai	South of Phu Noi, Khon Kaen province.[32]

See also

• List of dinosaur-bearing rock formations