# Phu Kradung Formation

The Early Cretaceous Phu Kradung Formation is the lowest member of the Mesozoic Khorat Group which outcrops on the Khorat Plateau in Isan, Thailand. This geological formation consists of micaceous, brown to reddish-brown siltstone beds with minor brown and grey shale and sandstone beds. Occasional lime-noduled conglomerate occurs.
The Phu Kradung Formation sediments were deposited in a lake-dominated floodplain cut by meandering and occasionally braided river channels.
The Phu Kradung Formation is considered, on the basis of recent vertebrae fossil discoveries, to be Late Jurassic in age. However, new palynology and biostratigraphic data suggests an age of Early Cretaceous for the upper section.
More recent datations trought detrital zircon U–Pb ages of samples from the conglomerates have stablished a lowermost age of late Early Jurassic (Toarcian), with a maximum depositional age of 180 Ma, which is older than the previously estimated Late Jurassic–Berriasian age based on fossil evidence. This discrepancy suggests the absence of syn-depositional zircons. The zircon data also help clarify the timing of the Indosinian III Event, placing the Indosinian III Unconformity between 201 and 182 Ma, marking a hiatus of about 20 million years. The Phu Kradung Formation deposition likely occurred after the Nam Phong Formation and may correlate with the Upper part of the last in the Khorat Basin subsurface.
Dinosaur remains have been recovered from this formation, although few have been referred to a specific genus.
Chalawan, an extinct genus of pholidosaurid mesoeucrocodylian, is currently known solely from its holotype, a nearly complete mandible collected in the early 1980s from a road-cut near the town of Nong Bua Lamphu in the upper part of the Phu Kradung Formation. This single specimen is the most well preserved vertebrate fossil that has been found from the formation. It contains a single species, Chalawan thailandicus.

## 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 Phu Kradung Formation :
| Genus | Presence | Material | Notes |
| Brachyopidae indet. | Phu Noi locality, Kham Muang district, Kalasin province. | Posterior part of the skull (KS34-1481) and two intercentra (KS34-1474 and KS34-1489). | |
| Brachyopoidea indet. | | Intercentra (TF 3328, TF 3329, and TF 3144). | Also found in the Klong Min Formation. |
| Brachyopoidea indet. | Khao Wong locality, Khao Wong district, Kalasin province. | Intercentrum (KS37-8). | |

### Archosaurs
#### Dinosaurs

Dinosaurs reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes |
| Mamenchisauridae indet. | | Kalasin province. | "Isolated posterior cervical vertebra" | |
| Metriacanthosaurinae indet. | | | "a nearly complete left tibia" | |
| Metriacanthosaurinae indet. | | | "Skull elements such as teeth, premaxillae, and maxillae as well as appendicular materials of more than one individual." | |
| Minimocursor | M. phunoiensis | Phu Noi, Kalasin province. | Partial articulated skeleton, isolated lower jaw & left leg. | A basal neornithischian. |
| Stegosauridae indet. | | | "Single dorsal vertebra". | Informally known as "Siamodracon altispinus". |
| Tyrannosauroidea indet. | | Phu Noi, Kalasin province. | Three isolated teeth. | A basal tyrannosauroid, related to Guanlong and Proceratosaurus. |

#### Pseudosuchians

Pseudosuchians reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes |
| Chalawan | C. thailandicus | | Mandible. | A pholidosaurid. |
| Indosinosuchus | I. kalasinensis | | | A teleosaurid. |
| Indosinosuchus | I. potamosiamensis | | Skulls and postcrania. | A teleosaurid. |
| Sunosuchus | S. thailandicus | | A mandible. | Reassigned to Chalawan. |
| Cf. Theriosuchus | Cf. T. sp. | Chong Chat, Nong Bua Lamphu province. | Part of a left dentary (CCC-1) and a lanceolate tooth (PRCMR 283). | An atoposaurid. |

#### Pterosaurs

Pterosaurs reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Rhamphorhynchidae indet. | | | Humerus. | Originally identified as an azhdarchid. | |

#### Turtles

Turtles reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes |
| Basilochelys | B. macrobios | Kham Phok, Mukdahan Province. | | A trionychoid. |
| Eucryptodira indet. | | | | |
| Kalasinemys | K. prasarttongosothi | Phu Noi locality, Kalasin Province. | Skull and shell material. | A xinjiangchelyid. |
| Phunoichelys | P. thirakhupti | Phu Noi locality, Kalasin Province. | Shell remains. | A xinjiangchelyid. |
| Yakemys | Y. multiporcata | Khorat Plateau. | Shell elements. | A macrobaenid. |

### Fish
#### Bony fish

Bony fish reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes |
| Ferganoceratodus | F. annekempae | Phu Noi. | | A lungfish. |
| Isanichthys | I. lertboosi | Phu Noi locality, Kalasin province. | 4 specimens. | A lepisosteiform. |
| Isanichthys | I. palustris | | A single, nearly complete specimen. | A lepisosteiform. |
| Khoratichthys | K. gibbus | | "Impression of a single articulated fish". | A ginglymodian. |
| Thaiichthys | T. buddhabutrensis | Phu Nam Jun, Kalasin Province. | | A lepisosteiform. |

#### Cartilaginous fish

Multiple fin spines have been found in the Phu Kradung Formation which cannot be precisely identified.
Cartilaginous fish reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes |
| Acrodus | A. kalasinensis | Kalasin province. | Teeth. | A hybodontiform. |
| Heteroptychodus | H. cf. H. kokutensis | | One almost complete tooth and 20 fragmentary crowns. | |
| ?Hybodontidae | | | Dermal denticles of 2 morphotypes. | A hybodontid. |
| Hybodus | aff. H. sp. | | "One almost complete anterior crown (SM2012-1-004) and a complete posterior tooth (SM2012-1-005)". | |
| Hybodus | H. sp. | | Teeth. | "Similar to the teeth of H. huangnidanensis (which is probably a junior synonym of H. antingensis)". |
| Jiaodontus | J. sp. | | 10 teeth. | A hybodontiform. |
| Lonchidion | L. sp. A | | SM2012-1-015-6 and 12 crowns. | A hybodontiform. |
| Lonchidion | L. sp. B | | Teeth and crowns. | A hybodontiform. |

### Plants

Plants reported from the Phu Kradung Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Xenoxylon | X. phyllocladoides | | Fossil wood. | | |