The Hasandong Formation () is a Lower Cretaceous geologic formation in South Korea. It has been dated to the Aptian to possibly the earliest Albian stage.
The Hasandong Formation could be distinguished from the underlying Nakdong Formation and the overlying Jinju Formation by frequent intercalations of reddish beds. The paleoenvironment of this formation represents a floodplain with a meandering channel including occasional pond deposits. Meanwhile, the paleoclimate has been interpreted as a seasonal alternation of wet and dry seasons.
Based on detrital zircons, Lee et al. 2010 and 2018 estimated the maximum depositional age of the formation at 118.0 ± 2.6 Ma, and suggested that the overlying Jinju Formation likely had a maximum depositional age of 112.4 ± 1.3 Ma. Chae et al. (2026) examined two fossiliferous localities of the upper Hasandong Formation on Yusu-ri, Jinju and on Jangguseom Island of Jungpyeong-ri, Hadong, and estimated the maximum depositional age on each site at 116.9 ± 1.5 Ma and 113.4 ± 1.4 Ma respectively. Fossils including plants, molluscs, diverse vertebrate remains including dinosaurs, turtles, and pterosaurs are known from this formation.
Fossil content Invertebrate fossils Few fragments of insects have been discovered from the formation.
Molluscs Molluscs reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesPlicatounioP. naktongensisP. okjuniP. yooniNagdongiaN. soniTrigonioidesT. jaehoiT. kodairaiT. tamuraiBrotiopsisB. kobayashiiB. naktongensisB. ryohoriensisB. wakinoensisViviparusV. sp.Architaenioglossan gastropod, probably V. keishoensisProbaicaliaP. katoensisHydrobiidae gastropod; species previously assigned to the genus Micromelania
Ostracods Ostracod carapaces have been discovered from the formation.
Ostracods reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesCyprideaC. cf. trita
Vertebrate fossils Actinopterygii Ray-finned fish reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesSinamiaS. sp.Partial SkeletonLepidotesL. sp.Partial Skeleton
Testudines Shell fragments of testudines have been discovered. Turtles reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesByeoljubuchelysB. yeosuensis Nearly complete carapace and plastron and associated post-cranial bonesA carettochelyid turtleProadocusP. hadongensisPartial SkeletonAn adocid turtle
Crocodylomorpha Several teeth remain have been reported but are not assigned to the specific clade.
Crocodylomorphs reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImages"Hadongsuchus"Lee, Hang-Jae. A New Protosuchian (Archosauria: Crocodyliformes) Skull from the Hasandong Formation (Lower Cretaceous) of Hadong, Korea. Master's thesis, Chungnam National University, 2005."H. acerdentis"Skullnomen nudum
Pterosaurs Pterosaurs reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesPterodactyloideaIndeterminateTeeth and a partial second wing phalanx Dental remains belong to either Boreopteridae or AnhanguerianDsungaripterusD.? cf. D. weiiIncomplete wing phalanx belonging to Dsungaripteridae
Dinosaurs Several indeterminate theropod teeth remains have been reported.
Dinosaurs reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesCarcharodontosauridaeIndeterminateTeethSome dental remains show similarities with AcrocanthosaurusHadrosauroideaIndeterminateToothTitanosauriformesZ. Dong, I. S. Paik, and H. J. Kim. 2001. A preliminary report on a sauropod from the Hasandong Formation (Lower Cretaceous), Korea. In T. Deng, Y. Wang (eds.), Proceedings of the Eighth Annual Meeting of the Chinese Society of Vertebrate Paleontology 41-53.IndeterminateA partial skeleton and several teeth showing different morphotypesIncludes Chiayusaurus sp. and Pukyongosaurus milleniumi, both of which are nomen dubiumTyrannosauroideaIndeterminateTooth, estimated crown length ~18mm
Eggs Unnamed dinosaur egg fossils have been reported. Eggs reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesTestudoolithusT. aff. curiosaTurtle eggs
Ichnofossils Tracks of theropods, sauropods and ornithopods have been discovered from the formation. Possible amphibian tracks are also known. Ichnofossils reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesPteraichnusP. koreanensisPterosaur tracksSauripesS. hadongensisThe oldest lizard tracks showing possible bipedalism, though potentially a nomen dubium due to insufficient description and problematic holotype designationDiplocraterionD. luniformeBeaconitesB. coronusCirculichnusC. montanusCochlichnusC. anguineusChondritesC. isp.HelminthopsisH. abeli & H. hieroglyphicaLaevicyclusL. isp.PlanolitesP. annularius, P. beverleyensis & P. montanusSkolithosS. magnus, S. verticalis & S. isp.SpirodesmosS. isp.TaenidiumT. barrettiThalassinoidesT. paradoxicus & T. suevicus
Paleoflora Macroflora of the Hasandong Formation suggests a shift toward seasonally semiarid conditions, dominated by conifers, compared to the underlying Nakdong Formation. Plants reported from the Hasandong FormationGenus Species Location Stratigraphic positionMaterialNotesImagesBrachyphyllumB. japonicumConifer with an unknown systematic positionCladophlebisC. denticulataC. (Eboracia?) lobifoliaC. (Klukia?) koraiensisC. shinshuensisElatocladusE. tennerimaConifer with an unknown systematic positionOnychiopsisO. elongataLeptosporangiate fernPtilophyllumP. sp.Bennettitales (extinct order of seed plants)RuffordiaR. sp.Schizaeaceae fernsTaeniopterisT.? sp. cf. T. auriculataThe specific systematic position of this form genus is unknown.ThallitesT. yabeiLiverwort
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See also List of dinosaur-bearing rock formations List of stratigraphic units with few dinosaur genera Seonso Conglomerate Haman Formation
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