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).^[1]

Bissekty Formation
Stratigraphic range: Mid-Late Turonian ~92–90 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Underlies	Aitym Formation
Overlies	Dzheirantui Formation
Thickness	up to 80 m (260 ft)
Lithology
Primary	Sandstone
Other	Conglomerate, mudstone, siltstone
Location
Coordinates	42.1°N 62.7°E / 42.1; 62.7
Approximate paleocoordinates	36.8°N 57.0°E / 36.8; 57.0
Region	Navoiy & Xorazm Regions
Country	Uzbekistan
Extent	Kyzylkum Desert
Bissekty Formation (Uzbekistan)

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.^[2]

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.^[2]

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.^[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.

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

Cartilaginous fish

Cartilaginous fishes of the Bissekty Formation
Genus	Species	Location	Stratigraphic position	Abundance	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	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

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	Location	Stratigraphic position	Abundance	Notes	Images
Aidachar	A. paludalis				An ichthyodectiform tolerant of brackish water
"Amia"	"A." limosa				A bowfin tolerant of brackish water, Nomen dubium[3]
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[4]
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	Location	Stratigraphic position	Material	Description	Images
Amtosaurus	A. archibaldi[5]				Reclassified as Bissektipelta[6]
Bactrosaurus	B. kyslkumensis			"Fragmentary dentary [=maxilla], vertebrae, tibia."[7]	Nomen dubium
Bissektipelta	B. archibaldi[6]			"Partial skull."[8]	An ankylosaur
Cionodon	C. kyslkumensis[5]				Reclassified as Bactrosaurus kyslkumensis[6]
Gilmoreosaurus	G. arkhangelskyi				Nomen dubium
Levnesovia	L. transoxiana			"Braincases"	A hadrosauroid
Turanoceratops[5]	T. tardabilis[5]				A ceratopsian[9]

Theropods

An indeterminate tyrannosauroid species, known from isolated teeth.^[10]

Carcharodontosauridae

Carcharodontosaurs of the Bissekty Formation
Genus	Species	Location	Stratigraphic position	Material	Description	Images
Carcharodontosauridae	Indeterminate			A partial posterior dorsal vertebra[11]
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	Location	Stratigraphic position	Material	Description	Images
Abavornis	A. bonaparti			Known from a partial coracoid[12]	A possible enantiornithine.[12] A possible second species of Abavornis in the Bissekty Formation is known from a partial coracoid.[12]
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.[12]
	E. walkeri			"Coracoid"[13]
Ichthyornis	I. minusculus			"Dorsal vertebra"[14]	An enantiornithine originally but incorrectly identified as a species of Ichthyornis.[15]
Incolornis	I. martini			Known from a partial coracoid[12]	A possible enantiornithine[12]
	I. silvae			Known from a partial coracoid[12]	A possible enantiornithine[12]
Kizylkumavis[5]	K. cretacea[5]			"Distal humerus"[13]	An enantiornithine
Kuszholia	K. mengi			"[Two] synsacra"[16]	An enantiornithine
Lenesornis[5]	L. maltshevskyi[5]			"Synsacrum"[13]	A possible enantiornithine
cf. Nanantius					An enantiornithine, similar to Nanantius eos
Sazavis[5]	S. prisca[5]			"Distal tibiotarsus"[17]	An enantiornithine
Zhyraornis[5]	Z. kashkarovi[5]			"Synsacrum"[17]
	Z. logunovi[5]			"Synsacrum"[17]

Other Theropods

Non-Enantiornithine Theropod dinosaurs of the Bissekty Formation
Genus	Species	Location	Stratigraphic position	Material	Description	Images
Caenagnathasia	C. martinsoni'			"[Two] partial mandibles"[18]	An elmisaurine caenagnathid
Dzharacursor	D. bissektensis			Right femur of a juvenile (holotype) with partial cranial and postcranial material[19]	An ornithomimosaur originally assigned to Archaeornithomimus.
Dzharaonyx	D. eski				An alvarezsaur
Euronychodon	E. asiaticus			A possible troodontid based on isolated teeth[20][21][22]
Itemirus	I. medullaris			A single small, damaged fossil braincase	A dromaeosaurine
Platanavis[5]	P. nana[5]			"Sacrum"[14]
Therizinosauroidea spp.[23]	Indeterminate			Partial crania also preserving some teeth and some postcranial elements including pedal bones (from multiple individuals)	At least two different therizinosauroids
Timurlengia[24]	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[25]
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	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.

Molluscs of the Bissekty Formation
Genus	Species	Location	Stratigraphic position	Abundance	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