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  • 21 Aug, 2019

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Ilek Formation
The Ilek Formation is a Lower Cretaceous geologic formation in Western Siberia. Many different fossils have been recovered from the formation. It overlies the Late Jurassic Tyazhin Formation and underlies the Albian Kiya Formation.

The formation was described by L. A. Ragozin in 1935. It consists of sands with sandstone concretions, layers of silts, clays and marls. Age of the formation, according to a crude 1962 estimate, is Valanginian(?) - Hauterivian - Barremian. Its thickness varies greatly, reaching 746 m in Teguldet borehole. A more recent 2024 estimate based on invertebrate and vertebrate fossils placed the age of the formation at Barremian–Aptian.

Age

Shestakovo 3 locality

The Ilek Formation conformably overlies the Upper Jurassic Tyazhin Formation. Gastropods and bivalves of Valanginian age have been recovered from the lower part of the formation, and gastropods and bivalves of Hauterivian to Barremian age have been found in the upper part, as well as Barremian ostracods. The age of the Shestakovo 1 locality is poorly constrained. Palynological samples from the Shestakovo 3 locality are characteristic of the Aptian. No angiosperm pollen has been found at this locality, indicating that it is older than the Albian. The upper layers of the formation do contain angiosperm pollen, indicating that part of the formation may extend into the Albian. The overlying Kiya Formation is upper Albian based on plant biostratigraphy.

Fauna

Amphibians

Amphibians reported from the Ilek Formation
Genus Species Locality Material Notes Images
Kiyatriton K. leshchinskiyi
  • Shestakovo 1
 Atlas, trunk vertebrae, fragmentary dentaries, femora, humerus, and nearly complete ilium A crown-group salamander
Kuzbassia K. sola
  • Shestakovo 1
 Two atlantal centra and a trunk vertebral centrum A karaurid

Mammaliamorphs

Mammaliamorphs reported from the Ilek Formation
Genus Species Locality Material Notes Images
Acinacodus A. tagaricus Right dentary fragment An amphidontid mammal
Baidabatyr B. clivosus
  • Bol'shoi Kemchug 3
 Upper premolar A multituberculate
Gobiconodon G. borissiaki 21 upper and lower jaws. A gobiconodont
G. hoburensis A fragmentary lower jaw.
Kemchugia K. magna A tooth An amphilestid mammal
Kiyatherium K. cardiodens A maxilla A zhangheotheriid mammal
Sibirotherium S. rossicum
  • Bol'shoi Kemchug 4
 M1 tooth; mandibular fragments A docodontan mammaliaform
Xenocretosuchus X. sibiricus Dental elements A tritylodontid mammaliamorph
Yermakia Y. domitor
  • Shestakovo 1
 A mandible A tinodontid mammal

Choristoderes

Choristoderes reported from the Ilek Formation
Genus Species Locality Material Notes Images
cf. Khurendukhosaurus K. cf. sp
  • Bol'shoi Kemchug 3
 Dorsal vertebra, sacral vertebra A non-neochoristodere choristodere
"Shestakovo choristodere"
  • Shestakovo
  • Bol'shoi Kemchug 3
  • Bol'shaya Terekhtul' 2
 Fragmentary dentaries, several vertebrae, rib fragments A possible neochoristodere
Choristodera Indeterminate
  • Smolenskii Yar
 Cervical centrum May represent a taxon distinct from both Khurendukhosaurus and the "Shestakovo choristodere"

Lizards

Lizards reported from the Ilek Formation
Genus Species Locality Material Notes Images
Paramacellodidae Indeterminate
  • Kemchug assemblage
  • Kiya assemblage
Platynota Indeterminate
  • Kemchug assemblage
Xenosauridae Indeterminate
  • Kemchug assemblage
  • Kiya assemblage
 A knob-scaled lizard

Turtles

Turtles reported from the Ilek Formation
Genus Species Locality Material Notes Images
Kirgizemys A macrobaenid

Crocodylomorphs

Crocodylomorphs reported from the Ilek Formation
Genus Species Locality Material Notes Images
Kyasuchus K. saevi
  • Shestakovo 3
 A partial skull A shartegosuchid crocodyliform
Tagarosuchus T. kulemzini
  • Shestakovo 3
 Nearly complete skull A crocodyliform

Pterosaurs

Pterosaurs reported from the Ilek Formation
Genus Species Locality Material Notes Image
?Ctenochasmatidae Indeterminate
  • Bol'shoi Kemchug 3
Lonchognathosaurus L. cf. sp.
  • Novochernorechensk
 Wing metacarpal fragment A dsungaripterid
Ornithocheiridae Indeterminate
  • Shestakovo 1
Pterodactyloidea Indeterminate
  • Bol'shoi Kemchug 3

Dinosaurs

Sauropodomorphs

Sauropodomorphs reported from the Ilek Formation
Genus Species Locality Material Notes Images
Lithostrotia Indeterminate Caudal vertebrae Potentially three distinct taxa of titanosaur
Sibirotitan S. astrosacralis
  • Shestakovo 1
  • Shestakovo 3
 Vertebrae, sacrum, and pedal elements A somphospondylan sauropod

Ornithischians

Ornithischians reported from the Ilek Formation
Genus Species Locality Material Notes Images
Ornithischia Indeterminate
  • Shestakovo 1
  • Bol'shoi Kemchug 3
 Isolated teeth Originally identified as two distinct "hypsilophodontid" taxa
Psittacosaurus P. sibiricus
  • Shestakovo
 Several skeletons A ceratopsian
Stegosauria Indeterminate
  • Bol'shoi Kemchug 3
 Isolated teeth

Theropods

Theropods reported from the Ilek Formation
Genus Species Locality Material Notes Images
Evgenavis E. nobilis A set of limb elements A confuciusornithiform
Kiyacursor K. longipes
  • Shestakovo 1
 Partial skeleton including cervical and caudal vertebrae, cervical and dorsal ribs, a left scapulocoracoid, humeri, and much of both hind limbs A noasaurid theropod
Paraves Indeterminate Teeth May belong to either Microraptorinae or Troodontidae
Mystiornis M. cyrili
  • Shestakovo 1
 Isolated metatarsus An avisaurid enantiornithean
Paraves Indeterminate Teeth May belong to either Microraptorinae or Troodontidae
Tyrannosauroidea Indeterminate Teeth
Urbacodon U. cf. sp. Teeth A troodontid with unserrated teeth

See also

References

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  2. ^ Криштофович А. Н., ed. (1955). "Илекская свита". Геологический словарь. Vol. 1 (А-Л). Рипол Классик. p. 271. ISBN 9785458366533.
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  5. ^ Averianov, Alexander; Ivantsov, Stepan; Skutschas, Pavel; Faingertz, Alexey; Leshchinskiy, Sergey (2018). "A new sauropod dinosaur from the Lower Cretaceous Ilek Formation, Western Siberia, Russia". Geobios. 51 (1): 1–14. Bibcode:2018Geobi..51....1A. doi:10.1016/j.geobios.2017.12.004. ISSN 0016-6995.
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