The Andaikhudag Formation, in older literature referred to as Unduruh Formation or Ondorukhaa Formation, is an

Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

(

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by t ...

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma ( million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is pre ...

) geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

in Mongolia.Andaikhudag Formation
in the

Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Paleo ...

Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

remains diagnostic to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

level are among the fossils that have been recovered from the formation.Weishampel et al., 2004, pp.517-607

Fossil content

The following fossils have been reported from the

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

s and secondary

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s of the formation: ;Birds * ''

Ambiortus dementjevi ''Ambiortus'' is a prehistoric bird genus. The only known species, ''Ambiortus dementjevi'', lived sometime during the Barremian age between 136.4 and 125 million years agoHoltz, Thomas R. Jr. (2012). ''Dinosaurs: The Most Complete, Up-to-Da ...

''Kurochkin, 2000 - "Vertebrae and forelimb""Table 11.1," in Weishampel et al., 2004, p.214 * '' Holbotia ponomarenkoi''Zelenkov & Averianov, 2015 ;Insects * Hymenoptera ** '' Kotujisca kholbotensis''Rasnitsyn, 1991 ** '' Neoxyelula reducta''Rasnitsyn, 1993 ** '' Palaeoichneumon townesi''Kopylov, 2009 * Diptera ** ''

Syntemna tele ''Syntemna'' is a genus of flies belonging to the family Mycetophilidae. The species of this genus are found in Eurasia and Northern America. Species: * '' Loewiella asinduloides'' Meunier, 1904 * '' Loewiella brevitarsis'' Meunier, 1923 R ...

''Blagoderov, 2000 ** '' Ulaia communis''Kalugina, 1993 *

Coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

** ''

Allophalerus bontsaganensis ''Allophalerus'' is an extinct genus of beetle in the family Ommatidae. Systematics * †''Allophalerus antiquus'' (Ponomarenko 1964) Karabastau Formation, Kazakhstan, Oxfordian * †''Allophalerus aphaleratus'' (Ponomarenko 1969) Kyzyl-Ki ...

''Ponomarenko, 1997 ** ''

Tetraphalerus notatus ''Tetraphalerus'' is a genus of beetles in the family Ommatidae, It is currently known from two extant species native to South America and several fossil species from the Jurassic and Cretaceous of Asia. Systematics According to Kirejtshuk, ...

'' *

Plecoptera Plecoptera is an order of insects, commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the mos ...

** '' Accretonemoura radiata''Sinitshenkova, 1987

References

Bibliography

* * * * * * * * * * {{cite LSA , last=Sinitshenkova , first=N.D , year=1987 , title=Istopicheskoe razvitie vesiyanok , journal=Akademiya Nauk SSSR, Trudy Paleontologicheskogo Instituta , volume=221 , pages=1–142 Geologic formations of Mongolia Lower Cretaceous Series of Asia Cretaceous Mongolia Barremian Stage Hauterivian Stage Shale formations Sandstone formations Lacustrine deposits Paleontology in Mongolia Formations

Fossil content

See also

References

Bibliography