TheDjadochta formation(sometimestranscribedand also known asDjadokhta,Djadokata,orDzhadokhtskaya) is a highlyfossiliferousgeological formationin Central Asia,Gobi Desert,dating from theLate Cretaceousperiod, about 75 million to 71 million years ago. Thetype localityis the Bayn Dzak locality, famously known as theFlaming Cliffs.Reptile (including dinosaur) and mammal remains are among the fossils recovered from the formation.

Djadochta Formation
Stratigraphic range:Campanian,
~75–71Ma
Bayn Dzak (Flaming Cliffs), thetype localityof the Djadochta Formation
TypeGeological formation
Unit ofShamo Group
Sub-unitsBayn Dzak Member, Tugrugyin Member
UnderliesBarun Goyot Formation
OverliesAlagteeg Formation
AreaNemegt Basin,Ulan Nur Basin
Thicknessover 90 m (300 ft)
Lithology
PrimarySandstone
OtherMudstone
Type section
Named forShabarakh Usu (Bayn Dzak)
Named byBerkey & Morris
LocationFlaming Cliffs
Year defined1927
Coordinates44°08′19″N103°43′40″E/ 44.13861°N 103.72778°E/44.13861; 103.72778
Approximate paleocoordinates30°42′N9°12′E/ 30.7°N 9.2°E/30.7; 9.2
RegionÖmnögov
CountryMongolia
Thickness at type sectionabout 90 m (300 ft)

Excavation history

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Cretaceous-aged dinosaur fossil localities ofMongolia.Djadochta localities at area B.

The Djadochta formation was first documented and explored—though only a single locality—duringpaleontologicalexpeditions of theAmerican Museum of Natural Historyin 1922–1925, which were part of theCentral Asiatic expeditions.The expeditions were led byRoy Chapman Andrews,in company ofWalter Willis Grangeras chief paleontologist and field team. The team did extensive exploration at the Bayn Dzak (formerly Shabarakh Usu) region, which they nicknamedflaming cliffs,given that at sunset the sediments of this locality had a characteristic reddish color. Notable finds included the first known fossils ofOviraptor,Protoceratops,Saurornithoides,andVelociraptor,the first confirmed dinosaur eggs (a partial nest ofOviraptor), as well as fossil mammals. Some of these were briefly described byHenry Fairfield Osbornduring the ongoing years of the expeditions. In 1927 the formation was formally described and established by Berkey and Morris, with Bayn Dzak as thetype locality.[1][2]

In 1963 the Mongolian paleontologist Demberelyin Dashzeveg reported the discovery of a new fossiliferous locality of the Djadochta Formation: Tugriken Shireh.[3]During the 1960s to 1970s, Polish-Mongolian and Russian-Mongolian paleontological expeditions collected new, partial to complete specimens ofProtoceratopsandVelociraptorat this locality, making these dinosaur species a common occurrence in Tugriken Shireh.[4]Some of the most notable excavations made at Tugriken Shireh include theFighting Dinosaurs(ProtoceratopsandVelociraptorlocked in combat),[5][6]and abundant articulated,in situ(in the original pose), and sometimes complete skeletons ofProtoceratops.[7][8]

During the 1980s a jointSoviet-Mongolian paleontological expedition discovered several Mesozoic fossil-rich localities in the Gobi Desert of Mongolia. Among these sites, Udyn Sayr was discovered and examined by the expedition, regarding its age as Late Cretaceous. This new locality was predominantly rich inavimimidfossils, with a lesser abundance of mammal and other dinosaur fossils.[4]

In 1993 a collaborative expedition by the Mongolian Academy of Sciences and the American Museum of Natural History discovered a new fossil site within the Djadochta Formation, named Ukhaa Tolgod, which translates to "Brown Hills." This site has yielded a significant number of well-preserved fossils, including those of mammals, dinosaurs, lizards, and eggs. Most specimens are found in near-complete articulation, indicating excellent preservation conditions. Compared to other Mesozoic fossil sites, Ukhaa Tolgod stands out for its high fossil diversity.[9][10]

Description

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The modern-day Djadochta Formation is set in an arid habitat of sand dunes with little freshwater apart from oases andarroyos,in the Gobi Desert. The dominantlithologyof the Djadochta Formation is represented by non-marine,cementedreddish-orange and pale orange to light gray, medium to fine-grained sands andsandstones,which include minor deposits ofcalcareousconcretionsand orange-brown siltyclay.Less abundantsedimentationcomprisesconglomerates,siltstones,fluvial(water-deposited) sandstones, andmudstones.The entire thickness of the formation in theUlan Nur Basinis at least 80 m (260 ft). Severalaeolian processes(wind works) indicate the presence of large straight-crested dune-like structures, and smallerbarchan(crescent-shaped) and parabolic (poorly U-shaped) dunes across the formation.[11][12][10]Reddish sandstones are observed in numerous localities.[12][10]

Exposures at the Flaming Cliffs
  • Bayn Dzak(also spelled Bain Dzak, Bayanzag, Bayn Zag, Bayan Zag, or Shabarakh Usu; locally known asFlaming Cliffs): It is dominated by reddish-orange sandstones and well-sorted, unbedded, and medium-grained sands. The thickness of the strata at the Flaming Cliffs at least more than 30 m (98 ft). Less abundant lithology of Bayn Dzak includes cemented and poorly-cemented siltstones, mudstones, and grayish conglomerates. The latter are better exposed at western escarpments of the Flaming Cliffs.[13][12]Bayn Dzak is about 90 m (300 ft) in total thickness and can be divided into two sections: alternations of horizontally-bedded sandstone and mudstone in the lowermost part, and sandstone-dominated successions in the upper or main part.[14]
  • Tugriken Shireh(also spelled Tugrik, Toogreeg, Toogreek, Tugreek, Tugrug, Turgrugyin, Tugrugeen, Tögrögiin, Tugrikiin, or Tugrikin): This locality is about 30 m (98 ft) in thickness and characterized by poorly cemented, fine-grained sandstones that have colors varying from pink to yellowish-white. The predominant mineral isquartz,and lesser common minerals are represented by feldspars and lithic fragments. Bothcross-stratifiedand structureless sandstones are scattered across Tugriken Shireh.[15][12]
  • Udyn Sayr(also spelled Udan Sayr, Udan Sair, Ulaan Sair, or Üüden Sair): Sediments of this locality are exposed across a region of more than 60 km2(23 sq mi). It is divided into lower (thickness of at least more than 10 m (33 ft)) and upper (thickness of about 50 m (160 ft)) beds. The lower beds are fluvial originated and dominated by sandstones and mudstones. The upper beds are likely of aeolian origin and consist of reddish, cross-stratified and structureless sandstones.[16]
  • Ukhaa Tolgod(also spelled Oka Tolga): The strata exposed at Ukhaa Tolgod is dominated by reddish sandstones, with some sandstones containing small amounts of conglomeratic lenses and/or cobbles and pebbles. Conglomerate itself is in this site, and to a lesser level are mudstones and siltstones, which are thin and laterally restricted. Cross-stratified and fine-structured sandstones are particularly abundant at Ukhaa Tolgod.[17][10]
  • Zamyn Khondt(also spelled Dzamyn Khondt, Zamin Khond, or Dzamin Khond): This locality is characterized by reddish, well-sorted, and fine-grained sandstones with calcareous concretions. Some aeolian beds are present and are finely stratified to massive, having a visible thickness of about 20 m (66 ft).[16]

Stratigraphy and age

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The Djadochta formation occurs in theLate Cretaceousperiod of theCampanianstage.Magnetostratigraphicdatings from the Bayn Dzak and Tugriken Shireh localities suggest that the Djadochta Formation was deposited during a time of rapidly changingpolarityat about 75 million to 71million years ago.[12]

The Djadochta formation is separated into a lower Bayn Dzak Member and an upper Turgrugyin Member, which represent very similar depositional environments.[12]Furtherstratafrom the Bayn Dzak Member includes that of the Ukhaa Tolgod locality, and its overall age is regarded also within the Campanian.[10]

Based on thesuperpositionof the members, the Tugrugyin Memberoverliesthe Bayn Dzak Member making it somewhat younger, which indicates that the Bayn Dzak paleofauna lived somewhat earlier than that from Tugriken Shireh. However, it is not yet understood the precise temporal difference:[12]Localities within the Djadochta Formation are considered to represent a sequence of progressively younger sediments and thereby paleofaunas. Ukhaa Tolgod may be younger than both Bayn Dzak and Tugriken Shireh.[18]Based on their fossil record and strata, Udyn Sayr and Zamyn Khondt have been correlated with other Djadokhta localities, though fossils of Udyn Sayr may indicate that this locality is younger than Bayn Dzak and Tugriken Shireh.[19]

Examinations on the strata of the Alag Teg (also spelled Alag Teeg or Alag Teer) locality, once considered part of this formation, indicates that it belongs to a different geological formation: theAlagteeg Formation,which is slightly older than the overlying Djadochta Formation. Based on sediments and stratigraphic relationships, the lower part of the Bayn Dzak locality is correlated with the Alag Teg locality, making both sections part of the Alagteeg Formation. The upper or main part of the former locality is considered part of the Djadochta Formation itself, as it shares similar lithology and stratigraphic relationships with Tugriken Shireh.[14]

Stratigraphy of the Djadochta Formation[12][14]
Formation Time period Member Lithology Thickness Image
Barun Goyot EarlyMaastrichtian Poorly cemented, fine and medium-grained red to reddish-brown sandstones. ~110 m (360 ft)
Djadochta Campanian
Turgrugyin Pale orange to light gray (sometimes yellowish-white) sands and sandstones. 30 m (98 ft)
Bayn Dzak Reddish-orange, crossbedded, and structureless sandstones, with minor deposits of brown siltstones and mudstones. 90 m (300 ft)
Alagteeg EarlyCampanian
Santonian
"lower Bayn Dzak" Alternating reddish brown mudstone and horizontally laminated sandstone, with ripple cross laminations and rhizoliths. ~15 m (49 ft)

Depositional environment

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Based on strata and rockfacies(such as sandstones andcaliche) of the formation and coeval units (Bayan Mandahu) it is currently agreed thatsedimentsof the Djadochta Formationwere depositedbywind activityin arid paleoenvironments comprising sand dunes with a warmsemi-aridclimate.[20][12][14]Fluvial sedimentation at the Ukhaa Tolgod locality indicates the presence of short-livedwater bodiesduring the times of the formation, which also contributed to its deposition.[10]

Taphonomy

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Examples of the Djadochta Formation preservation: articulatedCitipati(top) andProtoceratops(bottom) specimens

A vast majority of articulated specimens from the Djadochta Formation are found in unstructured sandstones, indicating burialin situby high-energy sand-bearing events. Some buriedProtoceratopsindividuals are preserved in distinctive postures involving the body and head arched upwards, suggesting that the animals died in the process of trying to free themselves from the body of sand, where they eventually fossilized. As they were unable to escape burial, the sandy mass prevented carcasses from being scavenged by vertebrates. Most of these "buried" specimens are found with bite traces and large borings (tunnel-like holes made by small invertebrates) on bone joints areas and other surfaces, indicating that after death they were largely scavenged by invertebrates, such asskin beetles.[21][22][23]

It has been suggested that the repeated occurrence of these feeding traces at limb joints may reflect that the responsible scavengers focused on collagen at the joint cartilage of dried dinosaur carcasses as a source of nitrogen, which was very low in the arid Djadochta Formation environments.[24]

Examinations at the fossil preservation and sediments of Ukhaa Tolgod indicates that preserved animals were buried alive by catastrophic dune collapses. It is thought to have occurred when sand dunes became oversaturated with water resulting in their sudden downfall; heavy rainfall events likely acted as the triggering mechanism for this collapse.[9][25][10]Examples from the Ukhaa Tolgod preservation includeCitipati(brooding adults entombed atop nests and eggs);[26][27]Khaan(a pair in close proximity likely killed by a single collapse event);[28]andSaichangurvel(individual buried alive by a muddy dune).[29]

Paleobiota of the Djadochta Formation

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ArticulatedProtoceratopsfrom Tugriken Shireh. This dinosaur is one of the most common occurrences in the Djadochta Formation

Among fossils,Protoceratopsis extremely common in Djadochta localities. Bayn Dzak is reported as one of the localities with the highest concentration ofProtoceratopsfossils and has been noted as the "Protoceratopsfauna ".[30]Adjacent to Bayn Dzak, at Tugriken Shireh,Protoceratopsis also abundant.[15]Other common dinosaur components of the paleofauna includePinacosaurusandVelociraptor.[11]Small vertebrates like lizards and mammals are rather abundant and diverse, withAdamisaurusandKryptobaatarbeing the most abundant representatives.[29][31][30]The paleofauna of the Djadochta Formation is very similar in composition to the nearby and coeval-regardedBayan Mandahu FormationofInner Mongolia.The two formations share many of the same genera, but differ in species. For instance, the most common mammal in Djadochta isKryptobaatar dashzevegi,while in Bayan Mandahu it is the closely relatedK. mandahuensis.Similarly, the dinosaur fauna of Djadochta includesProtoceratops andrewsiandVelociraptor mongoliensis,which Bayan Mandahu yieldsP. hellenikorhinusandV. osmolskae.[20][32]

Although fossil plants are extremely rare in the Djadochta Formation, the great abundancy ofherbivorousProtoceratopsat the arid-deposited Tugriken Shireh locality indicates that it had a moderate coverage ofbushesor other low-growing plants.[15]

The relatively lowpaleobiodiversityand climate settings of the Djadochta suggest that these conditions contributed tostressedpaleoenvironments. Most of the fossil occurrences in the formation are occupied byProtoceratops,and small to medium-sizedankylosaurs,oviraptorids,anddromaeosauridsmake much of the overallpaleofauna.Large-bodiedanimals are absent or extremely rare in the formation. Comparisons with theNemegt Formationfurther reflects stressed paleoenvironments. In contrast to Djadochta, Nemegt has yielded an extensive diversity of large dinosaur taxa, such asDeinocheirus,Nemegtosaurus,Saurolophus,Tarbosaurus,orTherizinosaurus.Most of these taxa are herbivorous, which combined with themesic(well-watered) settings of the Nemegt Formation allowed the development of giant herbivores, in contrast to the stressed Djadochta Formation. Another indicative of stressed paleoenvironments is the almost non-existent amount of fullyaquatic animals.Turtles are rarely recovered, and most are terrestrial such asZangerlia.[30]It is suggested that most of the fragmented hadrosaur, tyrannosaur and sauropod remains across the formation likely belong to non-endemic,passing by species.[30]

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

Flora

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Genus Species Location Material Notes Images
Radicites R. gobiensis Bayn Dzak "Twenty plant roots."[33] Atracheophyte,likelyconifer.

Amphibians

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Genus Species Location Material Notes Images
Gobiates Indeterminate Udyn Sayr "Partial skeleton with partial urostyle."[34] A frog.

Crocodylomorphs

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Genus Species Location Material Notes Images
Artzosuchus A. brachicephalus Udyn Sayr "Partial skull."[35] Acrocodylomorph.
Gobiosuchus G. kielanae Bayn Dzak "Multiple specimens with partial skulls and skeletons."[36][37] Agobisuchid.
G.? parvus Udyn Sayr "Partial skull and skeleton."[38][39] Agobisuchid.
Shamosuchus S. djadochtaensis Bayn Dzak, Ukhaa Tolgod "Two skulls and partial skeleton."[40][41] Aparalligatorid.

Lizards

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Genus Species Location Material Notes Images
Adamisaurus A. magnidentatus Bayn Dzak, Tugriken Shireh, Ukhaa Tolgod "Skulls and skeletons from multiple specimens."[42][29] Ateiid.Also present in theBarun Goyot FormationandBayan Mandahu Formation.
Aiolosaurus A. oriens Ukhaa Tolgod "Incomplete skull and partial skeleton."[29] Avaranoid.
Carusia C. intermedia Bayn Dzak, Ukhaa Tolgod "Skulls from multiple specimens."[29] Acarusiid.Also present in theBarun Goyot FormationandBayan Mandahu Formation.
Cherminotus C. longifrons Tugriken Shireh, Ukhaa Tolgod "Skulls and partial skeleton."[29] Avaranoid.Also present in theBarun Goyot Formation.
Ctenomastax C. parva Zos "Incomplete skull."[29] Aniguanid.Also present in theBarun Goyot Formation.
Dzhadochtosaurus D. giganteus Tugriken Shireh "Partially complete skull."[43] Amacrocephalosaur.
Eoxanta E. lacertifrons Ukhaa Tolgod "Incomplete skull."[29] Ascincomorph.Also present in theBarun Goyot Formation.
Estesia E. mongoliensis Bayn Dzak, Ukhaa Tolgod "Partial skulls and teeth."[29] Amonstersaur.Also present in theBarun Goyot Formation.
Flaviagama F. dzerzhinskii Tugriken Shireh "Skull and two vertebrae."[44] Apriscagamid.
Globaura G. venusta Bayn Dzak, Ukhaa Tolgod "Partial skulls."[29] Ascincomorph.Also present in theBarun Goyot Formation.
Gobiderma G. pulchrum Udyn Sayr, Ukhaa Tolgod "Skulls and skin impressions."[29] Amonstersaur.Also present in theBarun Goyot Formation.
Gobinatus G. arenosus Ukhaa Tolgod "Partial skull."[29] Ateiid.Also present in theBarun Goyot Formation.
Hymenosaurus H. clarki Ukhaa Tolgod "Partial skull."[29] Ascincomorph.
Isodontosaurus I. gracilis Bayn Dzak, Tugriken Shireh, Ukhaa Tolgod, Zos "Numerous skulls and a partial skeleton."[29] Aniguanian.Also present in theBayan Mandahu Formation.
Macrocephalosaurus Indeterminate Ukhaa Tolgod "Partial skull and skeleton."[29] Ateiid.Also present in theBarun Goyot Formation.
Mimeosaurus M. crassus Bayn Dzak, Ukhaa Tolgod, Zos Wash "Partially complete skulls."[29] Anacrodont.Also present in theBayan Mandahu Formation.
Myrmecodaptria M. microphagosa Ukhaa Tolgod "Single skull."[29] Agekkotan.
Ovoo O. gurval Little Ukhaa Tolgod "Partial skull."[45] Avaranid.
Parmeosaurus P. scutatus Ukhaa Tolgod "Articulated skull and skeleton."[29] Ascincomorph.
Phrynosomimus P. asper Ukhaa Tolgod "Two partial skulls."[29] Anacrodont.Also present in theBarun Goyot Formation.
Priscagama P. gobiensis Bayn Dzak, Ukhaa Tolgod "Incomplete skulls."[29] Anpriscagamid.Also present in theBarun Goyot Formation.
Saichangurvel S. davidsoni Ukhaa Tolgod "Complete skull and skeleton in articulation."[46] Aniguanian.
Slavoia S. darevskii Ukhaa Tolgod "Skulls and skeleton."[29] Ascincomorph.Also present in theBarun Goyot Formation.
Telmasaurus T. grangeri Bayn Dzak "Partial skull and skeleton."[47][29] Avaranid.
Temujinia T. ellisoni Tugriken Shireh, Ukhaa Tolgod "Several partial skulls."[29] Aniguanid.
Tchingisaurus T. multivagus Ukhaa Tolgod "Partial skull."[29] Ateiid.
Unnamedscincomorph Indeterminate Ukhaa Tolgod "Partial skull."[29] Ascincomorph.
Varanoideaindet. Indeterminate Ukhaa Tolgod "Partial maxilla and vertebra."[29] Avaranoid.
Zapsosaurus Z. sceliphros Tugriken Shireh "Two partial skulls."[29] Aniguanid.

Mammals

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Genus Species Location Material Notes Images
Asiatherium A. reshetovi Udyn Sayr "Articulated skull and skeleton."[48] Ametatherian.
Bulganbaatar B. nemegtbaataroides Bayn Dzak, Ukhaa Tolgod "Partial skull, and other remains."[49][9] Amultituberculate.
Catopsbaatar C. catopsaloides Ukhaa Tolgod Not specified.[9] Adjadochtatheriid.Also present in theBarun Goyot Formation.
Chulsanbaatar C. vulgaris Ukhaa Tolgod "Skull and partial skeleton."[9] Amultituberculate.Also present in theBarun Goyot Formation.
Deltatheridium D. pretrituberculare Bayn Dzak, Ukhaa Tolgod "Partial skull and skeleton remains."[50][51] Atribosphenid.
Deltatheroides D. cretacicus Bayn Dzak "Partial skull."[50] Adjadochtatheriid.
Djadochtatherium D. matthewi Bayn Dzak, Tugriken Shireh "Partial skulls."[52][53] Adjadochtatheriid.
Hyotheridium H. dobsoni Bayn Dzak "Partial skull."[50] Atherian.
Indeterminate Ukhaa Tolgod Not specified.[9] Atherian.
Kamptobaatar K. kuczynskii Bayn Dzak, Ukhaa Tolgod "Partial skull, and other remains."[54][9] Amultituberculate.
Kennalestes K. gobiensis Bayn Dzak, Ukhaa Tolgod "Nearly complete skull, and other remains."[55][9] Aneutherian.
Kryptobaatar K. dashzevegi Bayn Dzak, Tugriken Shireh, Ukhaa Tolgod "Skulls and skeleton remains from several specimens."[54][31] Adjadochtatheriid.GobibaatarandTugrigbaatarare considered synonyms of this taxon.[56]
Maelestes M. gobiensis Ukhaa Tolgod "Partial skull with skeleton."[57] Acimolestid.
Mangasbaatar M. udanii Udyn Sayr "Skulls and partial skeleton from two specimens."[58] Adjadochtatheriid.
Nemegtbaatar N. gobiensis Ukhaa Tolgod Not specified.[9] Amultituberculate.Also present in theBarun Goyot Formation.
Sloanbaatar S. mirabilis Bayn Dzak, Ukhaa Tolgod "Complete skull, and other remains."[54][9] Amultituberculate.
Tombaatar T. sabuli Ukhaa Tolgod "Partial skull."[59] Adjadochtatheriid.
Ukhaatherium U. nessovi Ukhaa Tolgod "Partial to nearly complete skeletons from several specimens."[60][61][62] Aneutherian.
Zalambdalestes Z. lechei Bayn Dzak, Tugriken Shireh "Skulls and skeletons from several specimens."[50][63] Aneutherian.

Pterosaurs

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Genus Species Location Material Notes Images
Azhdarchidaeindet. Indeterminate Tugriken Shireh "Indeterminate bone inside the gut cavity of aVelociraptor."[64] Anazhdarchid.

Turtles

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Genus Species Location Material Notes Images
Nanhsiungchelyidaeindet. Indeterminate Abdrant Nuru "Three shell fragments."[65] Ananhsiungchelyid.
Indeterminate Bayn Dzak "Partial shells."[65] Ananhsiungchelyid.
Indeterminate Udyn Sayr "Two shell fragments."[65] Ananhsiungchelyid.
Zangerlia Z. dzamynchondi Zamyn Khondt "Partial shell."[66] Ananhsiungchelyid.
Z. ukhaachelys Ukhaa Tolgod "Partial skull and skeleton."[67] Ananhsiungchelyid.

Dinosaurs

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Ornithischians

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Ankylosaurids
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Genus Species Location Material Notes Images
Minotaurasaurus M. ramachandrani Ukhaa Tolgod [Two] complete skulls, mandibles, and first cervical half-ring.[68][69] Anankylosauridpreviously thought to be a junior synonym ofTarchia,but is now considered to be a valid and distinct taxon.
Pinacosaurus P. grangeri Bayn Dzak, Ukhaa Tolgod [Three] skulls, mandibles, predentary, cervical vertebrae, dorsal vertebrae, caudal vertebrae, ribs, scapula, coracoids, humerus, radius, ulna, ilium, femora, tibia, fibula, pelvis, manus, tail club handles, cervical half-rings, osteoderms, and a nearly complete skeleton lacking a skull.[70][71][72] Anankylosauridalso known from theAlagteeg FormationandBayan Mandahu Formation.
Ankylosauridaeindet. Indeterminate Zamyn Khondt Partially complete postcranial skeleton within situosteoderms.[73] Previously referred toSaichania,but is now referred to asAnkylosauridaeindet., or cf.Pinacosaurus.[73]
Ceratopsians
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Genus Species Location Material Notes Images
Bainoceratops B. efremovi Bayn Dzak "Partial vertebrae."[74] Aprotoceratopsid.May be synonymous withProtoceratops.[75]
Bagaceratops Indeterminate Udyn Sayr "Skull with partial skeleton."[19] Aprotoceratopsid.Indeterminate betweenBagaceratopsandProtoceratops.[19]
Protoceratops P. andrewsi Bayn Dzak, Tugriken Shireh, Udyn Sayr, Zamyn Khondt "Multiple partial to complete specimens."[76][7][77][8][19] Aprotoceratopsid.
P. hellenikorhinus Bor Tolgoi, Udyn Sayr "Partial cranial remains."[78] Aprotoceratopsid.
Protoceratopsidaeindet. Indeterminate Ukhaa Tolgod "Numerous skulls and remains."[79][80] Aprotoceratopsid.
Udanoceratops U. tschizhovi Udyn Sayr "Skull and fragmented skeleton elements."[81] A giantleptoceratopsid.
Hadrosaurs
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Genus Species Location Material Notes Images
Hadrosauroideaindet. Indeterminate Tugriken Shireh "Fragmented remains from juveniles."[82][83] Ahadrosauroid.
Plesiohadros P. djadokhtaensis Alag Teeg "Skull and partial body elements."[83] Ahadrosauroid.Actually hails from theAlagteeg Formation.[84]
Pachycephalosaurs
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Genus Species Location Material Notes Images
Goyocephale G. lattimorei Boro Khovil "Partial skull and skeleton."[85] Apachycephalosaurid.Locality sediments may belong to this formation.[85][86]

Saurischians

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Sauropods
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Genus Species Location Material Notes Images
Sauropodaindet. Indeterminate Not specified.[87] Not specified.[87] Asauropod.
Theropods
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Alvarezsaurs
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Genus Species Location Material Notes Images
Alvarezsauridaeindet. Indeterminate Tugriken Shireh "Partial skull, braincase, and skeleton elements of two specimens."[88][89] Analvarezsauridalso known as the Tugriken Shireh alvarezsaur. Uncertainly referred asParvicursorsp.[89]
Kol K. ghuva Ukhaa Tolgod "A well-preserved right foot."[90] A largealvarezsaurid.Its classification has been criticized.[91]
Shuvuuia S. deserti Ukhaa Tolgod "Multiple specimens with skull and skeletons."[92][93][94][90][95] Analvarezsaurid.
UndescribedAlvarezsauridae Indeterminate Bayn Dzak "Partial pelvic girdle and hindlimb."[96] Analvarezsaurid.
Indeterminate Gilvent Wash Not given.[90] Analvarezsaurid.
Birds
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Genus Species Location Material Notes Images
Apsaravis A. ukhaana Ukhaa Tolgod "Partial postcranial skeleton."[97] Abasalornithurinebird.
Elsornis E. keni Tugriken Shireh "Partial articulated skeleton lacking the skull."[98] Anenantiornithe.
Gobipteryx G. minuta Ukhaa Tolgod "Partial skull."[99] Anenantiornithine.Also present in theBarun Goyot Formation.
Protoceratopsidovum P. fluxuosum Bayn Dzak "Partial eggs."[100] Eggs probably laid by a bird.[101]
P. minimum Baga Tariach, Tugriken Shireh "Clutch of four eggs and one pole of egg."[100] Eggs probably laid by a bird.[101]
P. sincerum Bayn Dzak, Tugriken Shireh "Multiple eggs and shells."[100] Eggs probably laid by a bird.[101]
Styloolithus S. sabathi Bayn Dzak "Partial to complete eggs."[101] Eggs probably laid by a bird.
Dromaeosaurs
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Genus Species Location Material Notes Images
Tsaagan T. mangas Ukhaa Tolgod "Skull and partial skeleton."[102] Adromaeosaurid
Velociraptor V. mongoliensis Bayn Dzak, Chimney Buttes, Gilvent Wash, Tugriken Shireh, Udyn Sayr, Ukhaa Tolgod "Multiple partial to complete specimens."[103][104][105][106][107][108] Adromaeosaurid.
UndescribedDromaeosauridae Indeterminate Abdrant Nuru "Claw."[109] Adromaeosaurid.
Indeterminate Zos Wash "Frontal region."[102] Adromaeosaurid.Differs fromTsaagan.[102]
Halszkaraptorines
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Genus Species Location Material Notes Images
Halszkaraptor H. escuilliei Ukhaa Tolgod "Partial skeleton with complete skull."[110] Ahalszkaraptorine.
Mahakala M. omnogovae Tugriken Shireh "Fragmented skull and skeleton."[111] Ahalszkaraptorine.
Ornithomimosaurs
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Genus Species Location Material Notes Images
Aepyornithomimus A. tugrikinensis Tugriken Shireh "Nearly complete foot."[112] Anornithomimid.
Ornithomimosauriaindet. Indeterminate Ukhaa Tolgod "Partial braincase, jaw tips, ribs, and vertebral fragments".[113][114] Anornithomimid.
Oviraptorosaurs
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Genus Species Location Material Notes Images
Avimimus A. portentonsus Udyn Sayr "Partial skull and skeleton."[115][116] Anavimimid.Its locality origin has been disputed and may hail from theNemegt Formation.[117]
Citipati C. osmolskae Ukhaa Tolgod "Multiple specimens with partial to nearly complete skeletons, an embryo, eggs and nesting individuals."[118][119][120][27] Anoviraptorid.
Elongatoolithus E. frustrabilis
E. subtitectorius
Khaan K. mckennai Ukhaa Tolgod "Several specimens with partial to complete skeletons and skulls."[119][121][28] Anoviraptorid.
Macroolithus M. mutabilis "Eggs." Eggs probably laid by anoviraptorid
Oviraptor O. philoceratops Bayn Dzak "Partial skeleton with skull, associated with a nest and juvenile."[122][120][27] Anoviraptorid.
Oviraptoridaeindet. Indeterminate Zamyn Khondt "Nearly complete skeleton with skull."[123] Anoviraptoridalso known as the Zamyn Khondt oviraptorid. Uncertainly referred toCitipati.[119][120]
Indeterminate Zamyn Khondt "Nearly complete skull with atlas and axis."[124] Anoviraptorid.
Indeterminate Udyn Sayr "Assemblage of individuals."[27] Anoviraptorid.
Indeterminate Not specified. "Two skulls with characteristic high crest."[125][126][127] Anoviraptorid.
Troodontids
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Genus Species Location Material Notes Images
Almas A. ukhaa Ukhaa Tolgod "Skull with partial skeleton."[128] Atroodontid.
Archaeornithoides A. deinosauriscus Bayn Dzak "Partial skull."[129] Atroodontid?Uncertain relationships amongcoelurosaurs.[129][130]
Byronosaurus B. jaffei Ukhaa Tolgod "Skull and fragmentary skeleton."[131] Atroodontid.
Gobivenator G. mongoliensis Zamyn Khondt "Almost complete skeleton."[132] Atroodontid.
Saurornithoides S. mongoliensis Bayn Dzak "Skull with fragmentary skeleton."[133] Atroodontid.
Troodontidaeindet. Indeterminate Ukhaa Tolgod "Partial skeleton."[134] Atroodontid.
Indeterminate Ukhaa Tolgod "Juvenile skulls, skeleton, and one nest."[135][130] Atroodontid.Referred to eitherAlmas,[136][128]orByronosaurus.[130]
Indeterminate Ukhaa Tolgod "Fragmented skull and skeleton remains."[137] Atroodontid.Provisionally referred toSaurornithoides,[137]but now excluded.[133]
Indeterminate Ukhaa Tolgod "Partial skull and skeletons from two specimens."[93] Atroodontid.
Tyrannosaurids
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Genus Species Location Material Notes Images

Tyrannosauridaeindet.

Indeterminate Bayn Dzak Not specified.[32] Atyrannosaurid.
Indeterminate Khongil "Supraorbital, vertebra, rib, femur and metatarsals."[138] Atyrannosaurid.
Indeterminate Not specified. "Partial right ilium."[139] Atyrannosaurid.
Indeterminate Not specified. "Teeth."[20] Atyrannosaurid.
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Panoramic view of theFlaming Cliffs(Bayn Dzak), type locality of the Djadochta Formation

See also

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References

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