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.Suteetorn and Jarnyahran (1986). "Geological Map of Thailand 1:250,000, Sheet NE 48-14 (Roi Et).

The Phu Kradung Formation sediments were deposited in a lake-dominated floodplain cut by meandering and occasionally braided river channels.Racey and Goodall (2009). "Late Palaeozoic and Mesozoic Ecosystems in SE Asia". Geological Society. London. Special Publication 315 Pp 69-84.

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.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .

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

Amphibians Amphibians reported from the Phu Kradung Formation Genus Species Presence Material Notes ImagesBrachyopidae 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.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 ImagesMamenchisauridae indet.IndeterminatePhu Dan Ma, Kalasin provinceSuteethorn, S., Le Loeuff, J., Buffetaut, E., Suteethorn, V., and Wongko, K. 2013. First evidence of a mamenchisaurid dinosaur from the Upper Jurassic–Lower Cretaceous Phu Kradung Formation of Thailand. Acta Palaeontologica Polonica 58 (3): 459–469.Isolated posterior cervical vertebraIndeterminatePhu Noi, Ban Khok Sanam, Dan Luang and Chong Chat localitiesDental remainsMetriacanthosauridae indet.Indeterminate"a nearly complete left tibia"IndeterminatePartial skull and appendicular elements of more than one individualMetriacanthosauridae indet.IndeterminateMukdahanA single toothMinimocursorM. phunoiensisPhu Noi, Kalasin provincePartial articulated skeleton, isolated lower jaw, and left legA basal neornithischianStegosauridae indet.IndeterminateSingle dorsal vertebraUlansky, R. E., 2014. Evolution of the stegosaurs (Dinosauria; Ornithischia). Dinologia, 35 pp. [in Russian]. PDF.Informally known as "Siamodracon altispinus"Proceratosauridae indet.IndeterminatePhu Noi, Kalasin provinceThree isolated teethA basal proceraosaurid tyrannosauroid; closely related to Guanlong wucaii and Proceratosaurus bradleyi.UragasaurusU. kalasinensisPhu Noi, Kalasin provinceIsolated anterior dorsal vertebraA mamenchisaurid sauropod; other cranial and postcranial elements are present in the same locality but not referred to this taxon.

Pseudosuchians Pseudosuchians reported from the Phu Kradung Formation Genus Species Presence Material Notes Images ChalawanC. thailandicus Mandible.A pholidosaurid tethysuchianIndosinosuchusI. kalasinensisA teleosaurid thalattosuchianI. potamosiamensisSkulls and postcrania.A teleosaurid thalattosuchianSunosuchusS. thailandicusA mandible.Reassigned to Chalawan.Cf. TheriosuchusCf. T. sp.Chong Chat, Nong Bua Lamphu province.Part of a left dentary (CCC-1) and a lanceolate tooth (PRCMR 283).A atoposaurid neosuchian

Pterosaurs Pterosaurs reported from the Phu Kradung Formation Genus Species Presence Material Notes ImagesRhamphorhynchidae indet.Indeterminate Humerus. Originally identified as an azhdarchid.

Turtles Turtles reported from the Phu Kradung Formation Genus Species Presence Material Notes ImagesBasilochelysB. macrobiosKham Phok, Mukdahan Province.Tong, H.; Claude, J.; Naksri, W.; Suteethorn, V.; Buffetaut, E.; Khansubha, S.; Wongko, K. & Yuangdetkla, P. 2009. Basilochelys macrobios n. gen. and n. sp., a large cryptodiran turtle from the Phu Kradung Formation (latest Jurassic-earliest Cretaceous) of the Khorat Plateau, NE Thailand . In: Buffetaut, E.; Cuny, G.; Le Loeuff, J. & Suteethorn, V. (eds.). Late Palaeozoic and Mesozoic Ecosystems in SE Asia. Geological Society, London, Special Publications 315: 229-243.A trionychoid trionychian Eucryptodira indet.KalasinemysK. prasarttongosothiPhu Noi locality, Kalasin Province.Skull and shell material.A xinjiangchelyid turtlePhunoichelysP. thirakhuptiPhu Noi locality, Kalasin Province.Shell remains.A xinjiangchelyid turtleYakemysY. multiporcataKhorat Plateau.Shell elements.A macrobaenid turtle

Fish

Bony fish Bony fish reported from the Phu Kradung Formation Genus Species Presence Material Notes ImagesFerganoceratodusF. annekempaePhu Noi.A ceratodontiform lungfishF. martiniIsanichthysI. lertboosi Phu Noi locality, Kalasin province.4 specimens. A Lepidotid fishI. palustrisA single, nearly complete specimen.A lepidoti fishKhoratichthysK. gibbus"Impression of a single articulated fish".A lepisosteiform fishThaiichthysT. buddhabutrensisPhu Nam Jun, Kalasin Province.A lepisosteoidean 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 ImagesAcrodusA. kalasinensisKalasin province.Teeth.A acrodontid hybodontHeteroptychodusH. cf. H. kokutensisOne almost complete tooth and 20 fragmentary crowns.?HybodontidaeDermal denticles of 2 morphotypes.A hybodontid hybodont.Hybodusaff. H. sp."One almost complete anterior crown (SM2012-1-004) and a complete posterior tooth (SM2012-1-005)".H. sp.Teeth. "Similar to the teeth of H. huangnidanensis (which is probably a junior synonym of H. antingensis)".JiaodontusJ. sp.10 teeth.A lonchidiid hybodontiformLonchidionL. sp. ASM2012-1-015-6 and 12 crowns.A lonchidiid hybodontiformL. sp. BTeeth and crowns.A lonchidiid hybodontiform

Plants Plants reported from the Phu Kradung Formation Genus Species Presence Material Notes Images XenoxylonX. phyllocladoides Fossil wood.

See also Lists of dinosaur-bearing stratigraphic units List of stratigraphic units with indeterminate dinosaur fossils

References