The Bissekty Formation (sometimes referred to as Bissekt) is a geologic formation and Lagerstätte which crops out in the Kyzyl Kum desert of Uzbekistan, and dates to the Late Cretaceous Period. Laid down in the mid to late Turonian, it is dated to about 92 to 90 Ma (million years ago).
Description The lithology of the sediment largely consists of cross bedded sandstones with interbeds of massive sandstone, well cemented intraformational conglomerate, siltstones and mudstones. Most of the fossils are found as clasts within the conglomerates.
Fossil content The Bissekty Formation is characterised by a mix of marine, brackish, freshwater, and terrestrial animal fossils. This stands in contrast the strictly marine fossils found in the underlying Dzheirantui Formation, and indicates that the Bissekty was formed during the regression of a saltwater sea. The coastline expanded inland again in the upper portion of the Bissekty, represented by a proportional increase of fully aquatic species, which were almost completely absent from the middle period of the formation. Semi-aquatic species remained abundant during this middle period, and the geology of the formations indicates that a braided river system took the place of the coastline. Eventually the area was again completely underwater, during the time period represented by the later Aitym Formation, which preserves coastal marine sediments.Redman & Leighton, 2009
Vertebrates The Bissekty Formation is notable for preserving the most abundant Turonian land animal fossils in Eurasia, and the most diverse fauna of Late Cretaceous eutherians (placental mammals and relatives) in the world.
Listings and accompanying information are based on a survey of the Bissekty Formation published by Cory Redman and Lindsey Leighton in 2009 unless otherwise noted. Aquatic and semi-aquatic species are restricted to freshwater unless otherwise noted.
Amphibians An indeterminate species of salamander-like albanerpetontid amphibian. An indeterminate gobiatid species.
Amphibians of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Aralobatrachus A. robustus A frog Eoscapherpeton E. asiaticum A scapherpetontid salamander Gobiates G. sosedkoi A gobiatid frog Gobiates spp. Additional indeterminate species of Gobiates Itemirella I. cretacea A possible discoglossid frog Kizylkuma K. antiqua A possible discoglossid marine frog Mynbulakia M. surgai A batrachosauroidid salamander Nesovtriton N. mynbulakensis A cryptobranchoid salamander
Cartilaginous fish Cartilaginous fishes of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Images Cretodus C. crassidens A marine Pseudoscapanorhynchid Lamniform shark Heterodontus Indeterminate A marine bullhead shark Hispidaspis Indeterminate A sand shark tolerant of brackish water Hybodus Indeterminate A hybodontid tolerant of brackish water Ischyrhiza I. serra A sclerorhynchid tolerant of brackish water Myledaphus M. tritus A rhinobatoid tolerant of brackish water Polyacrodus Indeterminate A polyacrodontid tolerant of brackish water Scapanorhynchus S. rhaphiodon A goblin shark tolerant of brackish water
Crocodylomorphs Crocodylomorphs of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Kansajsuchus K. borealis A possible goniopholidid mesoeucrocodylian Tadzhikosuchus T. macrodentis A possible alligatoroid eusuchian Zholsuchus Z. procevus A possible mesoeucrocodylian Zhyrasuchus Z. angustifrons A possible eusuchian
Lizards An indeterminate gekkonid. An indeterminate priscagamid. An indeterminate scincid.
Lizards of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Buckantaus B. crassidens A macrocephalosaurid Ekshmer E. bissektensis A priscagamid
Mammals and other therapsids Mammaliaformes of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Aspanlestes A. aptap A zhelestid Bulaklestes B. kezbe An asioryctitherian Daulestes D. inobservabilis An asioryctitherian D. kulbeckensis An asioryctitherian Eoungulatum E. kudukensis A zhelestid Kulbeckia K. kulbecke A zalambdalestid Paranyctoides P. quadrans An eutherian Parazhelestes P. mynbulakensis A zhelestid P. robustus A zhelestid Shalbaatar S. bakht A symmetrodont Sulestes S. karakshi A deltatheroid Uchkudukodon U. nessovi An asioryctitherian Uzbekbaatar U. kizylkumensis A cimolodont Zhelestes Z. temirkazyk A zhelestid
Plesiosaurs Plesiosaurs of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Images Plesiosauria Indeterminate Marine, possibly tolerant of brackish water
Pterosaurs Pterosaurs of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Images Azhdarcho A. lancicollis Dzhara-Kuduk Taykarshinskaya unit An azhdarchid
Ray-finned fish Based on Brinkman et al (2025): Ray-finned fish of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes ImagesAcanthomorpha indet.An acanthomorph of uncertain affinities. Aidachar A. paludalis An ichthyodectiform tolerant of brackish water "Amia" "A." limosa A bowfin tolerant of brackish water. Potentially a nomen dubium, but some studies consider it valid. ?Anguilliformes indet.A potential eel of uncertain affinities.ArotusA. hieroglyphusA holostean, potentially a semionotiform, known from isolated scales. Atractosteus A. turanensis A gar tolerant of brackish water Belonostomus B. aciculiferus An aspidorhynchid Characiformes indet.A characiform of uncertain affinities.Clupeiformes indet.A clupeiform of uncertain affinities.cf. CoriopsAn osteoglossomorph.DiplomystusD. sp.An ellimmichthyiform.Gonorynchiformes indet.A gonorynchiform of uncertain affinities.NotogoneusN. sp.A beaked sandfish.cf. ParatarponAn elopiform. Polyodontidae indet. A paddlefish of uncertain affinities.
Dinosaurs
Sauropods Sauropods of the Bissekty Formation Genus Species Location Stratigraphic position Material Description Images Dzharatitanis D. kingi An anterior caudal vertebra. Originally described as a rebbachisaurid, a later study has suggested it was lognkosaurian titanosaur TitanosauriaIndeterminateCCMGE 628/12457, a braincase
Ornithischians
Ornithischians reported from the Bissekty Formation Genus Species Location Stratigraphic position Material Description Images Amtosaurus A. archibaldi"Dinosaur distribution (Bissekty Formation)." Weishampel, et al. (2004). Pg. 594. Reclassified as BissektipeltaAverianov, 2002 Bactrosaurus B. kyslkumensis "Fragmentary dentary [=maxilla], vertebrae, tibia.""Table 20.1," in Weishampel, et al. (2004). Page 442. Nomen dubium Bissektipelta B. archibaldi "Partial skull.""Table 17.1," in Weishampel, et al. (2004). Page 367. An ankylosaur Cionodon C. kyslkumensis Reclassified as Bactrosaurus kyslkumensisAverianov, 2002 Gilmoreosaurus G. arkhangelskyi Nomen dubium Levnesovia L. transoxiana "Braincases" A hadrosauroid Turanoceratops T. tardabilis A ceratopsianSues & Averianov, 2009
Theropods An indeterminate tyrannosauroid species, known from isolated teeth. Carcharodontosauridae Carcharodontosaurs of the Bissekty Formation Genus Species Location Stratigraphic position Material Description ImagesCarcharodontosauridae IndeterminateA partial posterior dorsal vertebraUlughbegsaurusU. uzbekistanensisA left maxilla, the ramus end of a left maxilla, and the posterior end of a right maxilla.A carcharodontosaurid theropod
Enantiornithines Enantiornithines of the Bissekty Formation Genus Species Location Stratigraphic position Material Description Images Abavornis A. bonaparti Known from a partial coracoid A possible enantiornithine. A possible second species of Abavornis in the Bissekty Formation is known from a partial coracoid. Catenoleimus C. anachoretus A possible enantiornithine Explorornis E. nessovi An enantiornithine. Possible third and fourth species of Explorornis in the Bissekty Formation are known from partial coracoids. E. walkeri "Coracoid""Table 11.1," in Weishampel, et al. (2004). Page 213. Ichthyornis I. minusculus "Dorsal vertebra" An enantiornithine originally but incorrectly identified as a species of Ichthyornis.Kurochkin. (1996). "A new Enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves)." Russian Academy of Sciences, special issue: 50pp. Incolornis I. martini Known from a partial coracoid A possible enantiornithine I. silvae Known from a partial coracoid A possible enantiornithine Kizylkumavis K. cretacea "Distal humerus" An enantiornithine Kuszholia K. mengi "[Two] synsacra""Table 11.1," in Weishampel, et al. (2004). Page 212. An enantiornithine Lenesornis L. maltshevskyi "Synsacrum" A possible enantiornithine cf. Nanantius An enantiornithine, similar to Nanantius eos Sazavis S. prisca "Distal tibiotarsus""Table 11.1," in Weishampel, et al. (2004). Page 214. An enantiornithine Zhyraornis Z. kashkarovi "Synsacrum" Z. logunovi "Synsacrum"
Other theropods Non-enantiornithine theropod dinosaurs of the Bissekty Formation Genus Species Location Stratigraphic position Material Description Images Caenagnathasia C. martinsoni "[Two] partial mandibles""Table 8.1," in Weishampel, et al. (2004). Page 166. An elmisaurine caenagnathid Dzharacursor D. bissektensis Right femur of a juvenile (holotype) with partial cranial and postcranial material An ornithomimosaur originally assigned to Archaeornithomimus DzharaonyxD. eskiAn alvarezsaur Euronychodon E. asiaticus Isolated teeth"Table 10.1," in Weishampel, et al. (2004). Page 199."Table 9.1," in Weishampel, et al. (2004). Page 185.Nesov, A. (1995). "Dinosaurs of Northern Eurasia: new data about assemblages, ecology and paleobiogeography." Scientific Research Institute of the Earth's Crust. St. Petersburg State University, St. Petersburg, Russia: 156 pp. + 14 pl. [in Russian with short English, German, and French abstracts]. A possible troodontid Itemirus I. medullaris A single small, damaged fossil braincase A dromaeosaurine Platanavis P. nana "Sacrum""Table 11.1," in Weishampel, et al. (2004). Page 216. Therizinosauroidea spp. Indeterminate Partial crania also preserving some teeth and some postcranial elements including pedal bones (from multiple individuals) At least two different therizinosauroids Timurlengia T. euotica Two braincases, dentary, and miscellaneous postcranial elements (from multiple individuals) A non-tyrannosaurid tyrannosauroid Urbacodon Unnamed species Isolated teeth A troodontid Zhyraornis Z. kashkarovi A possible ornithurine Dromaeosauridae indet.IndeterminatePedal phalanxA large indeterminate dromaeosauridAbelisauridae indet.IndeterminateAnterior dorsal neural archAn undescribed abelisaurid
Turtles An indeterminate trionychid (soft-shell) turtle species that was tolerant of brackish water.
Turtles of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes "Adocus" "Adocus" aksary An adocid tolerant of brackish water Anatolemys Indeterminate A "macrobaenid" tolerant of brackish water Khunnuchelys K. kizylkumensis A trionychid tolerant of brackish water Lindholmemys L. elegans A "lindholmemydid" tolerant of brackish water Shachemys S. ancestralis An adocid tolerant of brackish water
Invertebrates An indeterminate species of marine coral.
Arthropods Arthropods of the Bissekty Formation Genus Species Location Stratigraphic position Abundance Notes Linuparus L. dzheirantuiensis Marine A spiny lobster
Molluscs An indeterminate species of marine placenticeratid ammonite. An indeterminate species of marine teredinid shipworm. An indeterminate marine trigoniid bivalve. An indeterminate marine veneroid bivalve.