# Bissekty Formation

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.

### 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 | Notes |
| Aralobatrachus | A. robustus | A frog |
| Eoscapherpeton | E. asiaticum | A scapherpetontid salamander |
| Gobiates | G. sosedkoi | A gobiatid frog |
| Gobiates | 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 |

#### Cartilaginous fish

Cartilaginous fishes of the Bissekty Formation :
| Genus | Species | Notes | Images |
| Cretodus | C. crassidens | A marine Pseudoscapanorhynchid Lamniform shark | Cretodus_crassidens |
| Heterodontus | Indeterminate | A marine bullhead shark | Hornhai_(Heterodontus_francisci) |
| 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 | Myledaphus_skeleton |
| 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 | 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 | Notes |
| Aspanlestes | A. aptap | A zhelestid |
| Bulaklestes | B. kezbe | An asioryctitherian |
| Daulestes | D. inobservabilis | An asioryctitherian |
| Daulestes | D. kulbeckensis | An asioryctitherian |
| Eoungulatum | E. kudukensis | A zhelestid |
| Kulbeckia | K. kulbecke | A zalambdalestid |
| Paranyctoides | P. quadrans | An eutherian |
| Parazhelestes | P. mynbulakensis | A zhelestid |
| Parazhelestes | 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

An indeterminate acipenserid. An indeterminate albulid (bonefish) species. An indeterminate albulid (bonefish) species. An indeterminate pholidophoriform species.
Ray-finned fish of the Bissekty Formation :
| Genus | Species | Notes |
| Aidachar | A. paludalis | An ichthyodectiform tolerant of brackish water |
| "Amia" | "A." limosa | A bowfin tolerant of brackish water, Nomen dubium |
| Atractosteus | A. turanensis | A gar tolerant of brackish water |
| Belonostomus | B. aciculifer | An aspidorhynchid |
| Psephuroides | P. kazakhorum | A paddlefish |

#### Dinosaurs
##### Sauropods

Sauropod dinosaurs 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 | |
| Titanosauria | Indeterminate | | | CCMGE 628/12457, a braincase | | |

##### Ornithischians

| 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. |
Ornithischians reported from the Bissekty Formation :
| Genus | Species | Material | Description |
| Amtosaurus | A. archibaldi | | Reclassified as Bissektipelta |
| Bactrosaurus | B. kyslkumensis | "Fragmentary dentary [=maxilla], vertebrae, tibia." | Nomen dubium |
| Bissektipelta | B. archibaldi | "Partial skull." | An ankylosaur |
| Cionodon | C. kyslkumensis | | Reclassified as Bactrosaurus kyslkumensis |
| Gilmoreosaurus | G. arkhangelskyi | | Nomen dubium |
| Levnesovia | L. transoxiana | "Braincases" | A hadrosauroid |
| Turanoceratops | T. tardabilis | | A ceratopsian |

##### Theropods

An unnamed ornithomimosaur, known from fragmentary remains. An indeterminate tyrannosauroid species, known from isolated teeth.

###### Charcharodontosaurid

Carcharodontosaurs of the Bissekty Formation :
| Genus | Species | Material | Description |
| Carcharodontosauridae | Indeterminate | Dorsal Vertebra | |
| Carcharodontosauridae | Carcharodontosauridae indet. | A partial posterior dorsal vertebra | |
| Ulughbegsaurus | U. uzbekistanensis | A left maxilla, the ramus end of a left maxilla, and the posterior end of a right maxilla. | A probable carcharodontosaurid theropod |

###### Enantiornithines

Enantiornithines of the Bissekty Formation :
| Genus | Species | Material | Description |
| 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. |
| Explorornis | E. walkeri | "Coracoid" | An enantiornithine. Possible third and fourth species of Explorornis in the Bissekty Formation are known from partial coracoids. |
| Ichthyornis | I. minusculus | "Dorsal vertebra" | An enantiornithine originally but incorrectly identified as a species of Ichthyornis. |
| Incolornis | I. martini | Known from a partial coracoid | A possible enantiornithine |
| Incolornis | I. silvae | Known from a partial coracoid | A possible enantiornithine |
| Kizylkumavis | K. cretacea | "Distal humerus" | An enantiornithine |
| Kuszholia | K. mengi | "[Two] synsacra" | An enantiornithine |
| Lenesornis | L. maltshevskyi | "Synsacrum" | A possible enantiornithine |
| cf. Nanantius | | | An enantiornithine, similar to Nanantius eos |
| Sazavis | S. prisca | "Distal tibiotarsus" | An enantiornithine |
| Zhyraornis | Z. kashkarovi | "Synsacrum" | |
| Zhyraornis | Z. logunovi | "Synsacrum" | |

###### Other Theropods

Non-Enantiornithine Theropod dinosaurs of the Bissekty Formation :
| Genus | Species | Material | Description |
| Caenagnathasia | C. martinsoni' | "[Two] partial mandibles" | An elmisaurine caenagnathid |
| Dzharacursor | D. bissektensis | Right femur of a juvenile (holotype) with partial cranial and postcranial material | An ornithomimosaur originally assigned to Archaeornithomimus. |
| Dzharaonyx | D. eski | | An alvarezsaur |
| Euronychodon | E. asiaticus | A possible troodontid based on isolated teeth | |
| Itemirus | I. medullaris | A single small, damaged fossil braincase | A dromaeosaurine |
| Platanavis | P. nana | "Sacrum" | |
| 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 | | A troodontid, known from isolated teeth |
| Zhyraornis | Z. kashkarovi | | A possible ornithurine |

#### Turtles

An indeterminate trionychid (soft-shell) turtle species that was tolerant of brackish water.
Turtles of the Bissekty Formation :
| Genus | Species | 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.
Molluscs of the Bissekty Formation :
| Genus | Species | Notes |
| Crassatelites | Indeterminate | A marine crassatellid bivalve |
| Mytiloides | M. labiatus | A marine inoceramid bivalve |
| Plagiostoma | Indeterminate | A marine limoid bivalve |
| Quadratotrigonia | Indeterminate | A marine trigoniid bivalve |
| Xylophaga | Indeterminate | An indeterminate species of marine shipworm |