Djadochta Formation

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The Djadochta Formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation situated in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 million to 71 million years ago. The type locality is the Bayn Dzak locality, famously known as the Flaming Cliffs. Dinosaur, mammal, and other reptile remains are among the fossils that have been recovered from the formation.

Djadochta Formation
Stratigraphic range: Campanian,
~75–71 Ma
Sunset (20373858488).jpg
Bayn Dzak (Flaming Cliffs), the type locality of 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″N 103°43′40″E / 44.13861°N 103.72778°E / 44.13861; 103.72778Coordinates: 44°08′19″N 103°43′40″E / 44.13861°N 103.72778°E / 44.13861; 103.72778
Approximate paleocoordinates30°42′N 9°12′E / 30.7°N 9.2°E / 30.7; 9.2
RegionÖmnögov
Country Mongolia
Thickness at type sectionabout 90 m (300 ft)

Excavation historyEdit

 
Cretaceous-aged dinosaur fossil localities of Mongolia. Djadochta localities at area B.

The Djadochta Formation was first documented and explored—though only a single locality—during paleontological expeditions of the American Museum of Natural History in 1922–1925, which were part of the Central Asiatic Expeditions. The expeditions were led by Roy Chapman Andrews, in company of Walter Willis Granger as chief paleontologist and field team. The team did extensive exploration at the Bayn Dzak (formerly Shabarakh Usu) region, which they nicknamed Flaming Cliffs given that at sunset the sediments of this locality had a characteristic reddish color. Notable finds included the first known fossils of Oviraptor, Protoceratops, Saurornithoides, and Velociraptor, the first confirmed dinosaur eggs (a partial nest of Oviraptor), as well as fossil mammals. Some of these were briefly described by Henry Fairfield Osborn during the ongoing years of the expeditions. In 1927 the formation was formally described and established by Berkey and Morris, with Bayn Dzak as the type 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 of Protoceratops and Velociraptor at this locality, making these dinosaur species a common occurrence in Tugriken Shireh.[4] Some of the most notable excavations made at Tugriken Shireh include the Fighting Dinosaurs (Protoceratops and Velociraptor locked in combat),[5][6] and abundant articulated, in situ (in the original pose), and sometimes complete skeletons of Protoceratops.[7][8]

During the 1980s, a joint Soviet-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 in avimimid fossils, with a lesser abundance of mammal and other dinosaur fossils.[4]

In 1993 teams of a collaborative Mongolian-North American expedition (supported by the Mongolian Academy of Sciences and American Museum of Natural History) discovered a new fossil locality of the Djadochta Formation called Ukhaa Tolgod (meaning "Brown Hills"). Like previous localities, Ukhaa Tolgod has yielded a prominent abundance of well-preserved fossils, including high concentrations of mammal, dinosaur, lizard, and egg remains. A vast majority of specimens from this locality are usually found in near-complete articulation. Overall, when compared to other Mesozoic fossil sites, the diversity of fossils in Ukhaa Tolgod is unusually high.[9][10]

DescriptionEdit

The modern-day Djadochta Formation is set in an arid habitat of sand dunes with little freshwater apart from oases and arroyos, in the Gobi Desert. The dominant lithology of the Djadochta Formation is represented by non-marine, cemented reddish-orange and pale orange to light gray, medium to fine-grained sands and sandstones, which include minor deposits of calcareous concretions and orange-brown silty clay. Less abundant sedimentation comprises conglomerates, siltstones, fluvial (water-deposited) sandstones, and mudstones. The entire thickness of the formation in the Ulan Nur Basin is at least 80 m (260 ft). Several aeolian processes (wind works) indicate the presence of large straight-crested dune-like structures, and smaller barchan (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 as Flaming 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 is quartz, and lesser common minerals are represented by feldspars and lithic fragments. Both cross-stratified and 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 are 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 ageEdit

The Djadochta Formation occurs in the Late Cretaceous period of the Campanian stage. Magnetostratigraphic datings from the Bayn Dzak and Tugriken Shireh localities suggest that the Djadochta Formation was deposited during a time of rapidly changing polarity at about 75 million to 71 million 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] Further strata from the Bayn Dzak Member includes that of the Ukhaa Tolgod locality, and its overall age is regarded also within the Campanian.[10]

Based on the superposition of the members, the Tugrugyin Member overlies the 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: the Alagteeg 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 Early Maastrichtian 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 Early Campanian
Santonian
"lower Bayn Dzak" Alternating reddish brown mudstone and horizontally laminated sandstone, with ripple cross laminations and rhizoliths. ~15 m (49 ft)

Depositional environmentEdit

Based on strata and rock facies (such as sandstones and caliche) of the formation and coeval units (Bayan Mandahu) it is currently agreed that sediments of the Djadochta Formation were deposited by wind activity in arid paleoenvironments comprising sand dunes with a warm semi-arid climate.[20][12][14] Fluvial sedimentation at the Ukhaa Tolgod locality indicates the presence of short-lived water bodies during the times of the formation, which also contributed to its deposition.[10]

TaphonomyEdit

Examples of the Djadochta Formation preservation: articulated Citipati (top) and Protoceratops (bottom) specimens

A vast majority of articulated specimens from the Djadochta Formation are found in unstructured sandstones, indicating burial in situ by high-energy sand-bearing events. Some buried Protoceratops individuals 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 as skin 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 include Citipati (brooding adults entombed atop nests and eggs);[26][27] Khaan (a pair in close proximity likely killed by a single collapse event);[28] and Saichangurvel (individual buried alive by a muddy dune).[29]

Paleobiota of the Djadochta FormationEdit

 
Articulated Protoceratops from Tugriken Shireh. This dinosaur is one of the most common occurrences in the Djadochta Formation

Among fossils, Protoceratops is extremely common in Djadochta localities. Bayn Dzak is reported as one of the localities with the highest concentration of Protoceratops fossils and has been noted as the "Protoceratops fauna".[30] Adjacent to Bayn Dzak, at Tugriken Shireh, Protoceratops is also abundant.[15] Other common dinosaur components of the paleofauna include Pinacosaurus and Velociraptor.[11] Small vertebrates like lizards and mammals are rather abundant and diverse, with Adamisaurus and Kryptobaatar being the most abundant representatives.[29][31][30] The paleofauna of the Djadochta Formation is very similar in composition to the nearby and coeval-regarded Bayan Mandahu Formation of Inner Mongolia. The two formations share many of the same genera, but differ in species. For instance, the most common mammal in Djadochta is Kryptobaatar dashzevegi, while in Bayan Mandahu it is the closely related K. mandahuensis. Similarly, the dinosaur fauna of Djadochta includes Protoceratops andrewsi and Velociraptor mongoliensis, which Bayan Mandahu yields P. hellenikorhinus and V. osmolskae.[20][32]

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

The relatively low paleobiodiversity and climate settings of the Djadochta suggest that these conditions contributed to stressed paleoenvironments. Most of the fossil occurrences in the formation are occupied by Protoceratops, and small to medium-sized ankylosaurs, oviraptorids, and dromaeosaurids make much of the overall paleofauna. Large-bodied animals are absent or extremely rare in the formation. Comparisons with the Nemegt Formation further reflects stressed paleoenvironments. In contrast to Djadochta, Nemegt has yielded an extensive diversity of large dinosaur taxa, such as Deinocheirus, Nemegtosaurus, Saurolophus, Tarbosaurus, or Therizinosaurus. Most of these taxa are herbivorous, which combined with the mesic (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 fully aquatic animals. Turtles are rarely recovered, and most are terrestrial such as Zangerlia.[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 in small text; crossed out taxa are discredited.

FloraEdit

Genus Species Location Material Notes Images
Radicites R. gobiensi Bayn Dzak "Twenty plant roots."[33] A tracheophyte, likely conifer.

AmphibiansEdit

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

CrocodylomorphsEdit

Genus Species Location Material Notes Images
Artzosuchus A. brachicephalus Udyn Sayr "Partial skull."[35] A crocodylomorph.
Gobiosuchus G. kielanae Bayn Dzak "Multiple specimens with partial skulls and skeletons."[36][37] A gobisuchid.  
G.? parvus Udyn Sayr "Partial skull and skeleton."[38][39] A gobisuchid.
Shamosuchus S. djadochtaensis Bayn Dzak, Ukhaa Tolgod "Two skulls and partial skeleton."[40][41] A paralligatorid.
Zaraasuchus Z. shepardi Zos Canyon "Skull and fragmentary skeleton."[42] A gobisuchid.
Zosuchus Z. davidsoni Zos Canyon "Skull."[43] A shartegosuchoid.

LizardsEdit

Genus Species Location Material Notes Images
Adamisaurus A. magnidentatus Bayn Dzak, Tugriken Shireh, Ukhaa Tolgod "Skulls and skeletons from multiple specimens."[44][29] A teiid. Also present in the Barun Goyot Formation and Bayan Mandahu Formation.
Aiolosaurus A. oriens Ukhaa Tolgod "Incomplete skull and partial skeleton."[29] A varanoid.
Carusia C. intermedia Bayn Dzak, Ukhaa Tolgod "Skulls from multiple specimens."[29] A carusiid. Also present in the Barun Goyot Formation and Bayan Mandahu Formation.
Cherminotus C. longifrons Tugriken Shireh, Ukhaa Tolgod "Skulls and partial skeleton."[29] A varanoid. Also present in the Barun Goyot Formation.
Ctenomastax C. parva Zos "Incomplete skull."[29] An iguanid. Also present in the Barun Goyot Formation.
Dzhadochtosaurus D. giganteus Tugriken Shireh "Partially complete skull."[45] A macrocephalosaur.
Eoxanta E. lacertifrons Ukhaa Tolgod "Incomplete skull."[29] A scincomorph. Also present in the Barun Goyot Formation.
Estesia E. mongoliensis Bayn Dzak, Ukhaa Tolgod "Partial skulls and teeth."[29] A monstersaur. Also present in the Barun Goyot Formation.
Flaviagama F. dzerzhinskii Tugriken Shireh "Skull and two vertebrae."[46] A priscagamid.
Globaura G. venusta Bayn Dzak, Ukhaa Tolgod "Partial skulls."[29] A scincomorph. Also present in the Barun Goyot Formation.
Gobiderma G. pulchrum Udyn Sayr, Ukhaa Tolgod "Skulls and skin impressions."[29] A monstersaur. Also present in the Barun Goyot Formation.
Gobinatus G. arenosus Ukhaa Tolgod "Partial skull."[29] A teiid. Also present in the Barun Goyot Formation.
Hymenosaurus H. clarki Ukhaa Tolgod "Partial skull."[29] A scincomorph.
Isodontosaurus I. gracilis Bayn Dzak, Tugriken Shireh, Ukhaa Tolgod, Zos "Numerous skulls and a partial skeleton."[29] An iguanian. Also present in the Bayan Mandahu Formation.
Macrocephalosaurus Indeterminate Ukhaa Tolgod "Partial skull and skeleton."[29] A teiid. Also present in the Barun Goyot Formation.
Mimeosaurus M. crassus Bayn Dzak, Ukhaa Tolgod, Zos Wash "Partially complete skulls."[29] An acrodont. Also present in the Bayan Mandahu Formation.
Myrmecodaptria M. microphagosa Ukhaa Tolgod "Single skull."[29] A gekkotan.
Ovoo O. gurval Little Ukhaa Tolgod "Partial skull."[47] A varanid.
Parmeosaurus P. scutatus Ukhaa Tolgod "Articulated skull and skeleton."[29] A scincomorph.
Phrynosomimus P. asper Ukhaa Tolgod "Two partial skulls."[29] An acrodont. Also present in the Barun Goyot Formation.
Priscagama P. gobiensis Bayn Dzak, Ukhaa Tolgod "Incomplete skulls."[29] An priscagamid. Also present in the Barun Goyot Formation.
Saichangurvel S. davidsoni Ukhaa Tolgod "Complete skull and skeleton in articulation."[48] An iguanian.
Slavoia S. darevskii Ukhaa Tolgod "Skulls and skeleton."[29] A scincomorph. Also present in the Barun Goyot Formation.
Telmasaurus T. grangeri Bayn Dzak "Partial skull and skeleton."[49][29] A varanid.
Temujinia T. ellisoni Tugriken Shireh, Ukhaa Tolgod "Several partial skulls."[29] An iguanid.
Tchingisaurus T. multivagus Ukhaa Tolgod "Partial skull."[29] A teiid.
Unnamed scincomorph Indeterminate Ukhaa Tolgod "Partial skull."[29] A scincomorph.
Varanoidea indet. Indeterminate Ukhaa Tolgod "Partial maxilla and vertebra."[29] A varanoid.
Zapsosaurus Z. sceliphros Tugriken Shireh "Two partial skulls."[29] An iguanid.

MammalsEdit

Genus Species Location Material Notes Images
Asiatherium A. reshetovi Udyn Sayr "Articulated skull and skeleton."[50] A metatherian.  
Bulganbaatar B. nemegtbaataroides Bayn Dzak, Ukhaa Tolgod "Partial skull, and other remains."[51][9] A multituberculate.
Catopsbaatar C. catopsaloides Ukhaa Tolgod Not specified.[9] A djadochtatheriid. Also present in the Barun Goyot Formation.  
Chulsanbaatar C. vulgaris Ukhaa Tolgod "Skull and partial skeleton."[9] A multituberculate. Also present in the Barun Goyot Formation.
Deltatheridium D. pretrituberculare Bayn Dzak, Ukhaa Tolgod "Partial skull and skeleton remains."[52][53] A tribosphenid.
Deltatheroides D. cretacicus Bayn Dzak "Partial skull."[52] A djadochtatheriid.
Djadochtatherium D. matthewi Bayn Dzak, Tugriken Shireh "Partial skulls."[54][55] A djadochtatheriid.
Hyotheridium H. dobsoni Bayn Dzak "Partial skull."[52] A therian.
Indeterminate Ukhaa Tolgod Not specified.[9] A therian.
Kamptobaatar K. kuczynskii Bayn Dzak, Ukhaa Tolgod "Partial skull, and other remains."[56][9] A multituberculate.
Kennalestes K. gobiensis Bayn Dzak, Ukhaa Tolgod "Nearly complete skull, and other remains."[57][9] An eutherian.
Kryptobaatar K. dashzevegi Bayn Dzak, Tugriken Shireh, Ukhaa Tolgod "Skulls and skeleton remains from several specimens."[56][31] A djadochtatheriid. Gobibaatar and Tugrigbaatar are considered synonyms of this taxon.[58]
Maelestes M. gobiensis Ukhaa Tolgod "Partial skull with skeleton."[59] A cimolestid.
Mangasbaatar M. udanii Udyn Sayr "Skulls and partial skeleton from two specimens."[60] A djadochtatheriid.
Nemegtbaatar N. gobiensis Ukhaa Tolgod Not specified.[9] A multituberculate. Also present in the Barun Goyot Formation.
Sloanbaatar S. mirabilis Bayn Dzak, Ukhaa Tolgod "Complete skull, and other remains."[56][9] A multituberculate.
Tombaatar T. sabuli Ukhaa Tolgod "Partial skull."[61] A djadochtatheriid.
Ukhaatherium U. nessovi Ukhaa Tolgod "Partial to nearly complete skeletons from several specimens."[62][63][64] An eutherian.
Zalambdalestes Z. lechei Bayn Dzak, Tugriken Shireh "Skulls and skeletons from several specimens."[52][65] An eutherian.

PterosaursEdit

Genus Species Location Material Notes Images
Azhdarchidae indet. Indeterminate Tugriken Shireh "Indeterminate bone inside the gut cavity of a Velociraptor."[66] An azhdarchid.

TurtlesEdit

Genus Species Location Material Notes Images
Nanhsiungchelyidae indet. Indeterminate Abdrant Nuru "Three shell fragments."[67] A nanhsiungchelyid.
Indeterminate Bayn Dzak "Partial shells."[67] A nanhsiungchelyid.
Indeterminate Udyn Sayr "Two shell fragments."[67] A nanhsiungchelyid.
Zangerlia Z. dzamynchondi Zamyn Khondt "Partial shell."[68] A nanhsiungchelyid.
Z. ukhaachelys Ukhaa Tolgod "Partial skull and skeleton."[69] A nanhsiungchelyid.

DinosaursEdit

AlvarezsaursEdit

Genus Species Location Material Notes Images
Alvarezsauridae indet. Indeterminate Tugriken Shireh "Partial skull, braincase, and skeleton elements of two specimens."[70][71] An alvarezsaurid also known as the Tugriken Shireh alvarezsaur. Uncertainly referred as Parvicursor sp.[71]
Kol K. ghuva Ukhaa Tolgod "A well-preserved right foot."[72] A large alvarezsaurid. Its classification has been criticized.[73]  
Shuvuuia S. deserti Ukhaa Tolgod "Multiple specimens with skull and skeletons."[74][75][76][77][78] An alvarezsaurid.  
Undescribed Alvarezsauridae Indeterminate Bayn Dzak "Partial pelvic girdle and hindlimb."[79] An alvarezsaurid.
Indeterminate Gilvent Wash Not given.[77] An alvarezsaurid.

AnkylosauridsEdit

Genus Species Location Material Notes Images
Minotaurasaurus M. ramachandrani Ukhaa Tolgod [Two] complete skulls, mandibles, and first cervical half-ring.[80][81] An ankylosaurid previously thought to be a junior synonym of Tarchia, 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.[82][83][84] An ankylosaurid also known from the Alagteeg Formation and Bayan Mandahu Formation.  
Ankylosauridae indet. Indeterminate Zamyn Khondt Partially complete postcranial skeleton with in situ osteoderms.[85] Previously referred to Saichania, but is now referred to as Ankylosauridae indet., or cf. Pinacosaurus.[85]  

BirdsEdit

Genus Species Location Material Notes Images
Apsaravis A. ukhaana Ukhaa Tolgod "Partial postcranial skeleton."[86] A basal ornithurine bird.
Elsornis E. keni Tugriken Shireh "Partial articulated skeleton lacking the skull."[87] An enantiornithe.
Gobipteryx G. minuta Ukhaa Tolgod "Partial skull."[88] An enantiornithine. Also present in the Barun Goyot Formation.
Protoceratopsidovum' P. fluxuosum Bayn Dzak "Partial eggs."[89] Eggs probably laid by a bird.[90]
P. minimum Baga Tariach, Tugriken Shireh "Clutch of four eggs and one pole of egg."[89] Eggs probably laid by a bird.[90]
P. sincerum Bayn Dzak, Tugriken Shireh "Multiple eggs and shells."[89] Eggs probably laid by a bird.[90]
Styloolithus S. sabathi Bayn Dzak "Partial to complete eggs."[90] Eggs probably laid by a bird.

CeratopsiansEdit

Genus Species Location Material Notes Images
Bainoceratops B. efremovi Bayn Dzak "Partial vertebrae."[91] A protoceratopsid. May be synonymous with Protoceratops.[92]
Bagaceratops Indeterminate Udyn Sayr "Skull with partial skeleton."[19] A protoceratopsid. Indeterminate between Bagaceratops and Protoceratops.[19]  
Protoceratops P. andrewsi Bayn Dzak, Tugriken Shireh, Udyn Sayr, Zamyn Khondt "Multiple partial to complete specimens."[93][7][94][8][19] A protoceratopsid.  
P. hellenikorhinus Bor Tolgoi, Udyn Sayr "Partial cranial remains."[95] A protoceratopsid.  
Protoceratopsidae indet. Indeterminate Ukhaa Tolgod "Numerous skulls and remains."[96][97] A protoceratopsid.  
Udanoceratops U. tschizhovi Udyn Sayr "Skull and fragmented skeleton elements."[98] A giant leptoceratopsid.  

DromaeosaursEdit

Genus Species Location Material Notes Images
Tsaagan T. mangas Ukhaa Tolgod "Skull and partial skeleton."[99] A dromaeosaurid  
Velociraptor V. mongoliensis Bayn Dzak, Chimney Buttes, Gilvent Wash, Tugriken Shireh, Udyn Sayr, Ukhaa Tolgod "Multiple partial to complete specimens."[100][101][102][103][104][105] A dromaeosaurid.  
Undescribed Dromaeosauridae Indeterminate Abdrant Nuru "Claw."[106] A dromaeosaurid.
Indeterminate Zos Wash "Frontal region."[99] A dromaeosaurid. Differs from Tsaagan.[99]

HadrosaursEdit

Genus Species Location Material Notes Images
Hadrosauroidea indet. Indeterminate Tugriken Shireh "Fragmented remains from juveniles."[107][108] A hadrosauroid.
Plesiohadros P. djadokhtaensis Alag Teeg "Skull and partial body elements."[108] A hadrosauroid. Actually hails from the Alagteeg Formation.[109]

HalszkaraptorinesEdit

Genus Species Location Material Notes Images
Halszkaraptor H. escuilliei Ukhaa Tolgod "Partial skeleton with complete skull."[110] A halszkaraptorine.  
Mahakala M. omnogovae Tugriken Shireh "Fragmented skull and skeleton."[111] A halszkaraptorine.  

OrnithomimosaursEdit

Genus Species Location Material Notes Images
Aepyornithomimus A. tugrikinensis Tugriken Shireh "Nearly complete foot."[112] An ornithomimid.  
Ornithomimosauria indet. Indeterminate Ukhaa Tolgod "Partial braincase, jaw tips, ribs, and vertebral fragments".[113][114] An ornithomimid.

OviraptorosaursEdit

Genus Species Location Material Notes Images
Avimimus A. portentonsus Udyn Sayr "Partial skull and skeleton."[115][116] An avimimid. Its locality origin has been disputed and may hail from the Nemegt 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] An oviraptorid.  
Elongatoolithus E. frustrabilis
E. subtitectorius
Khaan K. mckennai Ukhaa Tolgod "Several specimens with partial to complete skeletons and skulls."[119][121][28] An oviraptorid.  
Macroolithus M. mutabilis "Eggs." Eggs probably laid by an oviraptorid
Oviraptor O. philoceratops Bayn Dzak "Partial skeleton with skull, associated with a nest and juvenile."[122][120][27] An oviraptorid.  
Oviraptoridae indet. Indeterminate Zamyn Khondt "Nearly complete skeleton with skull."[123] An oviraptorid also known as the Zamyn Khondt oviraptorid. Uncertainly referred to Citipati.[119][120]  
Indeterminate Zamyn Khondt "Nearly complete skull with atlas and axis."[124] An oviraptorid.  
Indeterminate Udyn Sayr "Assemblage of individuals."[27] An oviraptorid.
Indeterminate Not specified. "Two skulls with characteristic high crest."[125][126][127] An oviraptorid.  

PachycephalosaursEdit

Genus Species Location Material Notes Images
Goyocephale G. lattimorei Boro Khovil "Partial skull and skeleton."[128] A pachycephalosaurid. Locality sediments may belong to this formation.[128][129]  

TroodontidsEdit

Genus Species Location Material Notes Images
Almas A. ukhaa Ukhaa Tolgod "Skull with partial skeleton."[130] A troodontid.  
Archaeornithoides A. deinosauriscus Bayn Dzak "Partial skull."[131] A troodontid? Uncertain relationships among coelurosaurs.[131][132]
Byronosaurus B. jaffei Ukhaa Tolgod "Skull and fragmentary skeleton."[133] A troodontid.  
Gobivenator G. mongoliensis Zamyn Khondt "Almost complete skeleton."[134] A troodontid.  
Saurornithoides S. mongoliensis Bayn Dzak "Skull with fragmentary skeleton."[135] A troodontid.  
Troodontidae indet. Indeterminate Ukhaa Tolgod "Partial skeleton."[136] A troodontid.
Indeterminate Ukhaa Tolgod "Juvenile skulls, skeleton, and one nest."[137][132] A troodontid. Referred to either Almas,[138][130] or Byronosaurus.[132]  
Indeterminate Ukhaa Tolgod "Fragmented skull and skeleton remains."[139] A troodontid. Provisionally referred to Saurornithoides,[139] but now excluded.[135]
Indeterminate Ukhaa Tolgod "Partial skull and skeletons from two specimens."[75] A troodontid.

TyrannosauridsEdit

Genus Species Location Material Notes Images

Tyrannosauridae indet.

Indeterminate Bayn Dzak Not specified.[32] A tyrannosaurid.
Indeterminate Khongil "Supraorbital, vertebra, rib, femur and metatarsals."[140] A tyrannosaurid.
Indeterminate Not specified. "Partial right ilium."[141] A tyrannosaurid.
Indeterminate Not specified. "Teeth."[20] A tyrannosaurid.

GalleryEdit

Panoramic view of the Flaming Cliffs (Bayn Dzak), type locality of the Djadochta Formation

See alsoEdit

ReferencesEdit

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