# 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.
Dinosaur remains are among the fossils that have been recovered from the formation.

## Depositional environment

Baser 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. 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. Paleocurrent analysis suggests the sand channels at the time of deposition of the formation probably formed a braided channel environment.

## 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. | Humeri (SHM-PT 529 and SHM-PT 530) and a pelvic girdle (SHM-HY 231). | A frog. | |

### Reptiles
#### Dinosaurs

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

#### Pseudosuchians

Pseudosuchians reported from the Sao Khua Formation :
| Genus | Species | Presence | Material | Notes |
| Goniopholis | G. phuwiangensis | Phu Wiang district. | A dentary. | Reassigned to Sunosuchus. |
| Siamosuchus | S. phuphokensis | Phu Phok, Kok Prasil Sub-district, Phu Phan district, Sakon Nakhon province. | A partly articulated skeleton (PPC-1). | A goniopholidid. |
| Sunosuchus | S. phuwiangensis | Phu Wiang district. | A dentary. | Originally reported as Goniopholis phuwiangensis. |
| Theriosuchus | T. grandinaris | Phu Phok, Kok Prasil Sub-district, Phu Phan district, Sakon Nakhon province. | "PPC-2, a nearly complete rostrum and dentary". | An atoposaurid. |
| Varanosuchus | V. sakonnakhonensis | Phu Sung locality near Mueang Sakon Nakhon district, Sakon Nakhon province. | 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). | An atoposaurid. |

#### Pterosaurs

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

#### Turtles

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

### Fish
#### Bony fish

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

#### Cartilaginous fish

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