Bissekty Formation

The Bissekty Formation (sometimes referred to as Bissekt) is a geologic formation 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).[1]

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.[2]

Bissekty Formation
Stratigraphic range: Mid-Late Turonian
~92–90 Ma
TypeGeological formation
UnderliesAitym Formation
OverliesDzheirantui Formation
Thicknessup to 80 m (260 ft)
OtherConglomerate, mudstone, siltstone
Coordinates42°06′N 62°42′E / 42.1°N 62.7°ECoordinates: 42°06′N 62°42′E / 42.1°N 62.7°E
Approximate paleocoordinates36°48′N 57°00′E / 36.8°N 57.0°E
RegionNavoiy & Xorazm Regions
Country Uzbekistan
ExtentKyzylkum Desert
Bissekty Formation is located in Uzbekistan
Bissekty Formation
Bissekty Formation
Bissekty Formation (Uzbekistan)


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.[2]


An indeterminate species of marine coral.


Arthropods of the Bissekty Formation
Genus Species Location Stratigraphic position Abundance Notes


Linuparus dzheirantuiensis


A spiny lobster.


An indeterminate species of marine placenticeratid ammonite. An indeterminate species of marine teredinid shipworm. An indeterminate marine trigoniid bivalve. An indeterminate marine veneroid bivalve.

Molluscs of the Bissekty Formation
Genus Species Location Stratigraphic position Abundance Notes



A marine crassatellid bivalve.


Mytiloides labiatus

a marine inoceramid bivalve.



A marine limoid bivalve.



A marine trigoniid bivalve.



An indeterminate species of marine shipworm.


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.[2]

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.[2] Aquatic and semi-aquatic species are restricted to freshwater unless otherwise noted.


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 robustus

A frog.


Eoscapherpeton asiaticum

A scapherpetontid salamander.


Gobiates sosedkoi

A gobiatid frog.

Gobiates spp.

Additional indeterminate species of Gobiates.


Itemirella cretacea

A possible discoglossid frog.


Kizylkuma antiqua

A possible discoglossid frog. Marine.


Mynbulakia surgai

A batrachosauroidid salamander.

Cartilaginous fish


Crocodylomorphs of the Bissekty Formation
Genus Species Location Stratigraphic position Abundance Notes


Kansajsuchus borealis

A possible goniopholidid mesoeucrocodylian.


Tadzhikosuchus macrodentis

A possible alligatoroid eusuchian.


Zholsuchus procevus

A possible mesoeucrocodylian.


Zhyrasuchus angustifrons

A possible eusuchian.


An indeterminate gekkonid. An indeterminate priscagamid. An indeterminate scincid.

Lizards of the Bissekty Formation
Genus Species Location Stratigraphic position Abundance Notes


Buckantaus crassidens

A macrocephalosaurid.


Ekshmer bissektensis

A priscagamid.

Mammals and other therapsids

Mammaliaformes of the Bissekty Formation
Genus Species Location Stratigraphic position Abundance Notes


A. aptap

A zhelestid.


B. kezbe

An asioryctitherian.


D. inobservabilis

An asioryctitherian.

D. kulbeckensis

An asioryctitherian.


E. kudukensis

A zhelestid.


K. kulbecke

A zalambdalestid.


P. quadrans

A eutherian.


P. mynbulakensis

A zhelestid.

P. robustus

A zhelestid.


S. bakht

A symmetrodont.


S. karakshi

A deltatheroid.


U. nessovi

An asioryctitherian.


U. kizylkumensis

A cimolodont.


Z. temirkazyk

A zhelestid.


Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.


Plesiosaurs of the Bissekty Formation
Genus Species Location Stratigraphic position Abundance Notes Images



Marine, possibly tolerant of brackish water.


Ray-finned fish

An indeterminate acipenserid. An indeterminate albulid (bonefish) species. An indeterminate albulid (bonefish) species. An indeterminate pholidophoriform species.

A living Amia.


An unnamed ornithomimosaur, known from fragmentary remains.[8] An indeterminate tyrannosaurid species, known from isolated teeth.[9]


Enantiornithines reported from the Bissekty Formation
Genus Species Location Stratigraphic position Material Description Images


A. bonaparti

Known from a partial coracoid.[19]

A possible enantiornithine.[19] A possible second species of Abavornis in the Bissekty Formation is known from a partial coracoid.[19]


C. anachoretus

A possible enantiornithine.


E. nessovi

An enantiornithine. Possible third and fourth species of Explorornis in the Bissekty Formation are known from partial coracoids.[19]

E. walkeri



I. minusculus

"Dorsal vertebra."[16]

An enantiornithine originally but incorrectly identified as a species of Ichthyornis.[21]


I. martini

Known from a partial coracoid.[19]

A possible enantiornithine.[19]

I. silvae

Known from a partial coracoid.[19]

A possible enantiornithine.[19]


K. cretacea[3]

"Distal humerus."[20]

An enantiornithine.


K. mengi

"[Two] synsacra."[15]

An enantiornithine.


L. maltshevskyi[3]


A possible enantiornithine.

cf. Nanantius

An enantiornithine, similar to Nanantius eos.


S. prisca[3]

"Distal tibiotarsus."[22]

An enantiornithine.


Z. kashkarovi[3]


Z. logunovi[3]



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" aksary

An adocid tolerant of brackish water.



A "macrobaenid" tolerant of brackish water.


Khunnuchelys kizylkumensis

A trionychid tolerant of brackish water.


Lindholmemys elegans

A "lindholmemydid" tolerant of brackish water.


Shachemys ancestralis

An adocid tolerant of brackish water.


  1. ^ Averianov, Alexander; Sues, Hans-Dieter (April 2012). "Skeletal remains of Tyrannosauroidea (Dinosauria: Theropoda) from the Bissekty Formation (Upper Cretaceous: Turonian) of Uzbekistan". Cretaceous Research. 34: 284–297. doi:10.1016/j.cretres.2011.11.009. ISSN 0195-6671.
  2. ^ a b c d Redman & Leighton, 2009
  3. ^ a b c d e f g h i j k l m n "Dinosaur distribution (Bissekty Formation)." Weishampel, et al. (2004). Pg. 594.
  4. ^ a b Averianov, 2002
  5. ^ "Table 17.1," in Weishampel, et al. (2004). Page 367.
  6. ^ "Table 20.1," in Weishampel, et al. (2004). Page 442.
  7. ^ Sues & Averianov, 2009
  8. ^ Sues & Averianov, 2016
  9. ^ Archibald, James David; Sues, Hans-Dieter; Averianov, Alexander; King, Chris; Ward, David John; Tsaruk, Oleg; Danilov, Igor; Rezvyi, Anton; Veretennikov, Boris; Khodjaev, Anvar (1998). "Precis of the Cretaceous paleontology, biostratigtaphy and sedimentology at Dzharakuduk (Turonian?-Santonian), Kyzylkum Desert, Uzbekistan". Bulletin of the New Mexico Museum of Natural History and Science. 14: 21–27.
  10. ^ "Table 6.1," in Weishampel, et al. (2004). Page 139.
  11. ^ "Table 8.1," in Weishampel, et al. (2004). Page 166.
  12. ^ "Table 10.1," in Weishampel, et al. (2004). Page 199.
  13. ^ "Table 9.1," in Weishampel, et al. (2004). Page 185.
  14. ^ 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].
  15. ^ a b c d "Table 11.1," in Weishampel, et al. (2004). Page 212.
  16. ^ a b "Table 11.1," in Weishampel, et al. (2004). Page 216.
  17. ^ Stephen L. Brusatte; Alexander Averianov; Hans-Dieter Sues; Amy Muir; Ian B. Butler (2016). "New tyrannosaur from the mid-Cretaceous of Uzbekistan clarifies evolution of giant body sizes and advanced senses in tyrant dinosaurs". Proceedings of the National Academy of Sciences of the United States of America. 113 (13): 3447–3452. doi:10.1073/pnas.1600140113. PMC 4822578. PMID 26976562.
  18. ^ Averianov, A.O.; Sues, H.-D. (2007). "A new troodontid (Dinosauria: Theropoda) from the Cenomanian of Uzbekistan, with a review of troodontid records from the territories of the former Soviet Union". Journal of Vertebrate Paleontology. 27 (1): 87–98. doi:10.1671/0272-4634(2007)27[87:ANTDTF]2.0.CO;2.
  19. ^ a b c d e f g h Panteleev (1998). ""New species of enantiornithines (Aves: Enantiornithes) from the Upper Cretaceous of Central Kyzylkum." Russkii Ornitologicheskii Zhurnal". Ekspress-vy.pvsk. 35: 3–15.
  20. ^ a b c "Table 11.1," in Weishampel, et al. (2004). Page 213.
  21. ^ 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.
  22. ^ a b c "Table 11.1," in Weishampel, et al. (2004). Page 214.


Further reading


Abavornis is the name given to a genus of primitive birds from the Late Cretaceous, containing the single species A. bonaparti (named in honor of the Argentine paleontologist José Bonaparte). It was probably a member of the Enantiornithes, but as it is only known from a single broken coracoid (TsNIGRI 56/11915), which, however, looks typically enantiornithine, that assignment is tentative. The fossil is from Late Cretaceous Bissekty Formation (Coniacian, 89–86 MYA) in the Kyzylkum, Uzbekistan. Another partial coracoid (PO 4605) is very similar and is referred to as Abavornis sp.; it might belong to A. bonaparti and if so show some features which are damaged in the holotype.


Asiamericana (AY-zha-MER-i-KAHN-a – (Greek: Asia meaning Asia and New Latin Americas meaning Americas) is a dubious fossil fish genus known only from isolated teeth. It was named to recognize the occurrence of similar fossil teeth in Central Asia and North America. These regions once formed a connected land mass, during the Cretaceous period and were referred to as Asiamerica.

The teeth were discovered by L. A. Nesov in 1995. The findings were based on three teeth found in the central Kyzylkum desert, Uzbekistan, in deposits of the Bissekty Formation, dated to the mid-late Turonian age of the Late Cretaceous, about 90 million years ago. They are comparable to other teeth found in Kazakhstan and North America, which have been illustrated but not formally described. The type species is A. asiaticus.

The teeth themselves are straight, lack a constriction at the base, and lack serrations.


Azhdarcho is a genus of pterodactyloid pterosaur from the late Cretaceous Period of the Bissekty Formation (middle Turonian stage, about 92 million years ago) of Uzbekistan. It is known from fragmentary remains including the distinctive, elongated neck vertebrae that characterizes members of the family Azhdarchidae, which also includes such giant pterosaurs as Quetzalcoatlus. The name Azhdarcho comes from the Persian word azhdar (اژدر), a dragon-like creature in Persian mythology. The type species is Azhdarcho lancicollis. The specific epithet lancicollis is derived from the Latin words lancea (meaning "lance" or "spear") and collum ("neck").


Bissektipelta is a genus of herbivorous ankylosaurid dinosaur from the Upper Cretaceous of Uzbekistan. Bissektipelta is monospecific, containing only the species B. archibaldi.


Catenoleimus is a prehistoric bird genus from the Late Cretaceous. It lived during the mid-late Turonian stage, around 90 million years ago. A single species Catenoleimus anachoretus has been described, and this is only known from one piece of coracoid (specimen PO 4606), found in the Bissekty Formation of the Kyzyl Kum in present-day Uzbekistan.This bird appears to be a mid-sized enantiornithine, perhaps 20–25 cm long in life. The morphology of the bone is rather plesiomorphic compared to contemporary Enantiornithes.


Eoscapherpeton is an extinct genus of Late Cretaceous giant salamander from the Bissekty Formation.


Explorornis ("discovered bird", from Latin explōrō "to discover" and Ancient Greek ornis (όρνις) "bird") is a genus of Mesozoic birds which lived during the mid-late Turonian stage, around 90 million years ago, in the Bissekty Formation of the Kyzyl Kum, in present-day Uzbekistan.E. walkeri (specimen PO 4825) was originally placed in Enantiornis, but the description of the type species E. nessovi (PO 4819), showed that it was not congeneric with the South American Enantiornis, which makes far more sense considering biogeography and age. The two species are named after famous paleontologists: Lev Alexandrovich Nesov (1947–1995) and Cyril Alexander Walker.

These were all smallish birds, maybe 15–20 cm long in life, except E. walkeri which was probably more than 25 cm long.

Since only the coracoids are known, the phylogenetic position of these taxa is somewhat unresolved. They do resemble the more advanced Enantiornithes more than they do any other bird however. Confirmation of their placement with Euenantiornithes would still require more material however.


Gilmoreosaurus is the name given to a genus of dinosaur from the Cretaceous of Asia. The type species is Gilmoreosaurus mongoliensis. It is believed to be a hadrosaur or iguanodont from the Iren Dabasu Formation of Mongolia, dating to 70 Ma ago. Additional specimens have been described as distinct species, including G. atavus from the Khodzhakul Formation of Uzbekistan (120 Ma ago) and G. arkhangelskyi from the Bissekty Formation (89 Ma ago). However, these are based on very fragmentary remains, and their classification is dubious. An additional species, G. kysylkumensis (also from the Bissekty Formation) is sometimes included, though it has also been referred to the related genus Bactrosaurus.

The first Gilmoreosaurus fossil remains were collected by George Olsen in 1923 and consisted of disarticulated bones from several individuals at different localities. They were originally assigned to the genus Mandschurosaurus but later given the separate genus Gilmoreosaurus, which was characterized by its combination of basal iguanodontian and hadrosaurid traits. Although a consensus on the exact taxonomic placement of this genus remains unreached, a 2010 study by Prieto-Márquez and Norell places the animal in a closely related outgroup to Hadrosauridae, based on a reassessment of its taxonomic status using a large-sample phylogenic analysis.In 2003, evidence of tumors, including hemangiomas, desmoplastic fibroma, metastatic cancer, and osteoblastoma was discovered in fossilized Gilmoreosaurus skeletons. Rothschild et al. tested dinosaur vertebrae for tumors using computerized tomography and fluoroscope screening. Several other hadrosaurids, including Brachylophosaurus, Edmontosaurus, and Bactrosaurus, also tested positive. Although more than 10,000 fossils were examined in this manner, the tumors were limited to Gilmoreosaurus and closely related genera. The tumors may have been caused by environmental factors or genetic propensity.


Incolornis (meaning "inhabitant bird") is an extinct genus of basal birds from the Late Cretaceous (Coniacian, 89-86 mya). Remains have been found in the Bissekty Formation in Uzbekistan.

It is only known from fragmentary coracoids. The systematic position of the genus is unclear; it might have been an enantiornithine bird.

Two species are known, Incolonis silvae and Incolornis martini; the latter was initially placed in the genus Enantiornis. The estimated length of these animals was 135 mm for I. silvae and 220 mm for I. martini.


Kizylkumavis is a genus of enantiornithine birds which lived during the Late Cretaceous and is known from fossils found in the Bissekty Formation of the Kyzyl Kum, Uzbekistan.


Kuszholia (meaning "Milky Way bird" after the Kazakh term for the Milky Way, kus zholi) is the name given to a genus of primitive birds or bird-like dinosaurs from the Late Cretaceous. They were possibly coelurosaurs close to the ancestry of birds, although most scientists have considered it an avialan (either a primitive ornithuran or enantiornithine). Fossils were found in the Bissekty Formation in the Kyzyl Kum desert of Uzbekistan.

The genus contains a single species, K. mengi; a separate family has been erected for it (Kuszholiidae). It is known only from a series of small vertebrae, with prominent hollow chambers (pneumaticity).


Lenesornis is a genus of enantiornithine birds which lived during the Late Cretaceous about 78 mya and is known from fossils found in the Bissekty Formation in the Kyzyl Kum, Uzbekistan.


Levnesovia is a genus of hadrosauroid dinosaur from the Late Cretaceous Bissekty Formation of Uzbekistan. It was related to Bactrosaurus. The type species is L. transoxiana. The genus name honours the late Russian paleontologist Lev Nesov, and the specific name refers to the ancient region Transoxiana. It is known from the minority of the skull and would have reached around two meters in length.


Nesovtriton is an extinct genus of cryptobranchoid salamander known from the Late Cretaceous (Turonian age) of Bissekty Formation, in Uzbekistan. It was first named by Pavel P. Skutschas in 2009 and the type species is Nesovtriton mynbulakensis.


Tadzhikosuchus is an extinct genus of alligatoroid crocodilian from the Late Cretaceous of Tajikistan. To date it is mostly known from partial dentaries that show it to have been very similar to Diplocynodon. The two are differentiated by subtle differences in tooth position and tooth socket shape, and by differences in stratigraphy (Diplocynodon is known from the Paleogene and Neogene, making it younger). Three species have been named: the type species T. macrodentis, described by Efimov in 1982 from the lower Santonian-age Upper Cretaceous Yalovach Svita of Kansai, Tajikistan, in the Fergana Basin of Tajikistan; T. neutralis from the same location, by Efimov in 1988; and T. kizylkumensis from Turonian-age rocks of the Upper Cretaceous Bissekty Formation of Dzharakhuduk, Uzbekistan, by Nesov and colleagues in 1989. However, a 2000 review by Glenn Storrs and Mikhail Efimov could not differentiate between the species based on their type material, and recommended grouping the specimens of all three species under T. macrodentis. They also could not determine how Tadzhikosuchus and the contemporaneous Zhyrasuchus were related, or even if they were synonyms, due to the poor fossils available. The name of the Tadzhikosuchus is derived from the Russian spelling of the name of the former Soviet republic of Tajikistan.


Timurlengia is an extinct genus of tyrannosauroid theropod dinosaur found in Uzbekistan, in the Bissekty Formation in the Kyzylkum Desert, hailing from the Turonian age of the early Late Cretaceous. The type species is Timurlengia euotica.


Turanoceratops ("Turan horned face") is a genus of herbivorous ceratopsian dinosaur from the late Cretaceous Bissekty Formation of Uzbekistan. The fossils dated from the mid-late Turonian stage, roughly 90 million years ago. The skull bore a pair of long brow horns like those seen in the Ceratopsidae, although Turanoceratops appears to have been transitional between earlier ceratopsians and ceratopsids, and not a ceratopsid itself.


Zholsuchus is a genus of crocodyliform that may have been a goniopholidid mesoeucrocodylian, but is only known from scanty material (a right premaxilla, one of the bones of the tip of the snout). This specimen was found in the Coniacian-age Upper Cretaceous Bissekty Formation of Dzharakhuduk, Uzbekistan. Zholsuchus was described in 1989 by Lev Nesov and colleagues. The type species is Z. procevus. A 2000 review by Glenn Storrs and Mikhail Efimov designated Zholsuchus a dubious name.


Zhyraornis is a genus of prehistoric bird from the late Cretaceous period (middle Turonian, 92 mya). Its fossils have been found in Bissekty Formation deposits near Dzharakuduk in the Kyzyl Kum, Uzbekistan. Two species have been assigned to this genus: Zhyraornis kashkarovi and Zhyraornis logunovi. Both are known only from partial pelvic bones (synsacra).


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