Iren Dabasu Formation | |
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Stratigraphic range: | |
Type | Geological formation |
Overlies | Arshanto Formation |
Area | Erenhot (Erlian) city |
Thickness | Up to 500 m (1,600 ft) |
Lithology | |
Primary | Sandstone, claystone, siltstone |
Other | Glutenite |
Location | |
Coordinates | 43°48′N112°24′E / 43.8°N 112.4°E |
Approximate paleocoordinates | 43°06′N101°00′E / 43.1°N 101.0°E |
Region | Inner Mongolia |
Country | China |
Extent | Erlian Basin |
Type section | |
Named for | Iren Dabasu |
Named by | Osborn |
Year defined | 1922 |
The Iren Dabasu Formation (also known as Erlian Formation) is a Late Cretaceous geologic formation in the Iren Nor region of Inner Mongolia. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation. The formation was first described and defined by Henry Fairfield Osborn in 1922 and it is located in the Iren Nor region of China. [1]
It comprises continental clastic sediments consisting of light grey fine sandstones, coarse sandstones and glutenites as well as mottled claystones and siltstones. The fine-grained floodplain sediments and the coarse-grained sediments of the point bar formed a series of repeated frequently binary sedimentary rhythms. The “binary structure” of the sedimentary rhythms strongly indicates meandering stream deposits rather than braided river deposits as previously thought. [2] [3] As indicated by the fluvial and lacustrine sedimentation, the Iren Dabasu Formation was a large floodplain terrain with braided rivers and meanders that supported extensive vegetation, evidenced on the prominent palaeosol development and the numerous remains from herbivorous dinosaurs. [3] [2] Egg nests, caliche and paleosols seem to indicate periodic subaerial intervals, in addition, the presence of plesiosaur and hybodont shark remains (which are also known in the Bayan Shireh Formation) are indicatives of a river system with connections to the ocean. [4]
Based on the ostracod and charophyte assemblages of the Iren Dabasu Formation, Itterbeeck et al. 2005 suggested a potential correlation with those of the Nemegt Formation, making its age Late Campanian to Early Maastrichtian. [3] However, vertebrates point to an older date than the Campanian-Maastrichtian ages, the supposed deposition of ostracods were likely due to climatic conditions rather than age. [5] The turtle Khunnuchelys is known from both Iren Dabasu and Bayan Shireh equivalent units such as the Bostobe and Bissekty. [2] In addition, a giant caenagnathid similar to Gigantoraptor is now known from the Bayan Shireh Formation at the locality of Tsagan Teg. [5] Like the coeval Bayan Shireh Formation (and possibly Javkhlant Formation) in the Gobi Desert, the dinosaur fauna of the Iren Dabasu Formation includes tyrannosauroids, ornithomimids, therizinosaurs and oviraptorosaurs. [6]
However, strong evidence coming from biostratigraphic occurrences seems to support a correlation with the Bayan Shireh Formation, at least, with the upper boundary. For instance, both formations bear similar dinosaur taxa, such as therizinosaurs ( Erlikosaurus , Segnosaurus , Erliansaurus or Neimongosaurus ) and ornithomimosaurs ( Garudimimus or Archaeornithomimus ), these similarities are even more intensified by the discovery of Gigantoraptor and the giant unnamed caenagnathid from Bayan Shireh. In addition, the potential discovery of Alectrosaurus in both formations seems to be another indicative of a correlation. [7] [2] [5] Consequently, Averianov and Sues estimated the formation to be Santonian in age, roughly about 86 million and 83 million years ago. [2] However, palynological correlations suggest a Maastrichtian age. [8] Guo et al. 2018 supported a Late Cretaceous age based on U–Pb and paleomagnetic analyses, with a maximum depositional age of around 95.8 ± 6.2 million years ago. [9] A 2022 study describing new ornithomimosaurian material, however, suggested that while the vertebrate faunal assemblage indicates that the age of the formation is likely Turonian based on its similarity to the Bissekty Formation of Uzbekistan, the invertebrate faunal assemblage indicates a much later age (Campanian-Maastrichtian). [10]
The Iren Dabasu Formation is rich on dinosaur fauna, with multiple species described, in the other hand, mammals seem to be extremely absent. Compared, the fossil taxa between Iren Dabasu and Bayan Shireh are very similar, most notably therizinosaurs, tyrannosauroids, oviraptorosaurs and turtles. [11] [2] Although Gigantoraptor is the only described oviraptorosaur from the formation, Funston et al. 2019 described a new avimimid bonebed containing numerous individuals at different growth stages. Nevertheless, the fossils lacked enough diagnosis to be confined to a separate genus and species. [4] Deinonychosaurs are not very common across the formation, however an indeterminate troodontid about the size of Saurornithoides is known from three isolated specimens. [12] An isolated humerus of a pterosaur has also been found in this formation. [11]
Color key
| Notes Uncertain or tentative taxa are in small text; |
Theropods reported from the Iren Dabasu Formation | ||||||
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Taxon | Species | Location | Stratigraphic Position | Material | Notes | Images |
Alectrosaurus | A. olseni | "Virtually complete right hindlimb and left metatarsals." [13] | A tyrannosauroid. Potentially present in the Bayan Shireh Formation | |||
A. asiaticus | "Partial manus, metatarsus, vertebrae, limb elements." [14] | An ornithomimosaur originally identified as Ornithomimus . | ||||
Avimimidae spp. | Indeterminate | "Vertebrae and postcranial elements represented by at least six individuals." [4] | Avimimids at different growth stages. | |||
Indeterminate | "Beak from lower jaws." [15] | An oviraptorosaur. | ||||
E. bellamanus | "Cervical vertebrae and postcranial elements." [16] | |||||
G. erlianensis | "Lower jaws and much of the postcranial elements with very elongated hindlimbs." [17] | A giant oviraptorosaur. | ||||
N. yangi | "Two specimens with most of the axial column, many limb and girdle elements, and a partial dentary." [18] | A therizinosauroid. | ||||
Ornithomimosauria | Indeterminate | "A pelvis and sacrum." [10] | Likely distinct from Archaeornithomimus asiaticus, probably representing an early-diverging group within Ornithomimosauria. | |||
Indeterminate | A therizinosaurid similar to Segnosaurus and initially attributed to Alectrosaurus olseni . | |||||
Indeterminate | "Right and left metatarsals represented by three specimens." [12] | A troodontid. | ||||
Tyrannosauridae | Indeterminate | "75 fragments, which include premaxillary and lateral teeth, a fragmentary lacrimal, jugal, pterygoid, and ectopterygoid." [20] | A juvenile tyrannosaurid that may be related to Timurlengia based on phylogenetic analysis, [21] but detailed comparisons suggest it may be related to tyrannosaurines. [20] | |||
Urbacodon | U. norelli | A partial right dentary and associated teeth [22] | A troodontid. | |||
Ornithopods reported from the Iren Dabasu Formation | ||||||
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Genus | Species | Location | Stratigraphic Position | Material | Notes | Images |
B. johnsoni | "Cranial and postcranial material represented by more than eight specimens." [14] [23] [24] | A hadrosauroid. | ||||
G. mongoliensis | "Partial cranial and postcranial elements represented by more than ten specimens". [14] [25] [24] | A hadrosauroid originally identified as Mandschurosaurus . | ||||
S. irenensis | "Egg fossils." [26] | Eggs shells attributed to Spheroolithus. | ||||
Sauropods reported from the Iren Dabasu Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic Position | Material | Notes | Images |
S. saihangaobiensis | "Numerous cervical, dorsal and caudal vertebrae and some postcranial elements." [27] | A titanosaur. | ||||
Angiosperms reported from the Iren Dabasu Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic Position | Material | Notes | Images |
Indeterminate | "Pollen grain." [28] | |||||
Buttinia sp. | Indeterminate | "Spores and pollen." [28] | Angiosperm pollen. | |||
Cranwellia sp. | Indeterminate | "Pollen grain." [28] | Angiosperm pollen. | |||
Momipites sp. | Indeterminate | "Pollen grain." [28] | Angiosperm pollen. | |||
Normapolles sp. | Indeterminate | "Pollen grain." [28] | Angiosperm pollen. | |||
Sabalpollenites sp. | Indeterminate | "Pollen grain." [28] | Angiosperm pollen. | |||
Tricolpate -morph | Indeterminate | "Pollen grain." [28] | Angiosperm palynomorph. | |||
Triporate -morph | Indeterminate | "Pollen grain." [28] | Angiosperm palynomorph. | |||
Ulmideipites sp. | Indeterminate | "Pollen grain." [28] | Angiosperm pollen. | |||
Ulmipollenites sp. | Indeterminate | "Spores and pollen." [28] | Angiosperm pollen. | |||
Gymnosperms reported from the Iren Dabasu Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic Position | Material | Notes | Images |
Bisaccate -morph | Indeterminate | "Spores and pollen." [28] | Gymnosperm palynomorph. | |||
Indeterminate | "Pollen grain." [28] | Gymnosperm pollen. | ||||
Cheirolepidiacean -morph | Indeterminate | "Pollen grain." [28] | Gymnosperm palynomorph. | |||
Ephedripites sp. | Indeterminate | "Spores and pollen." [28] | Gymnosperm pollen. | |||
Exesipollenites sp. | Indeterminate | "Spores and pollen." [28] | Gymnosperm pollen. | |||
Monosulcate -morph | Indeterminate | "Pollen grain." [28] | Gymnosperm pollen. | |||
Indeterminate | "Pollen grain." [28] | Gymnosperm pollen. | ||||
Spores reported from the Iren Dabasu Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic Position | Material | Notes | Images |
Cyathidites sp. | Indeterminate | "Spores and pollen grain." [28] | Spore palynomorph. | |||
Ischyosporites sp. | Indeterminate | "Spores." [28] | Spore palynomorph. | |||
Leptolepidites sp. | Indeterminate | "Spores." [28] | Spore palynomorph. | |||
Triplanosporites sp. | Indeterminate | "Spores." [28] | Spore palynomorph. | |||
Enigmosaurus is a genus of therizinosauroid that lived in Asia during the Late Cretaceous period. It was a medium-sized, ground-dwelling, bipedal herbivore that represents the third therizinosaur taxon from the Bayan Shireh Formation, although it is known from the lower part. The genus is monotypic, including only the type species E. mongoliensis, known from a well preserved pelvis and other tentative body remains.
Garudimimus is a genus of ornithomimosaur that lived in Asia during the Late Cretaceous. The genus is known from a single specimen found in 1981 by a Soviet-Mongolian paleontological expedition in the Bayan Shireh Formation and formally described in the same year by Rinchen Barsbold; the only species is Garudimimus brevipes. Several interpretations about the anatomical traits of Garudimimus were made in posterior examinations of the specimen, but most of them were criticized during its comprehensive redescription in 2005. Extensive undescribed ornithomimosaur remains at the type locality of Garudimimus may represent additional specimens of the genus.
Alectrosaurus is a genus of tyrannosauroid theropod dinosaur that lived in Asia during the Late Cretaceous period, about some 96 million years ago in what is now the Iren Dabasu Formation.
Achillobator is a genus of large dromaeosaurid theropod dinosaur that lived during the Late Cretaceous period about 96 million to 89 million years ago in what is now the Bayan Shireh Formation of Mongolia. The genus is currently monotypic, only including the type species A. giganticus. The first remains were found in 1989 during a Mongolian-Russian field expedition and later described in 1999. Remains at the type locality of Achillobator may represent additional specimens. It represents the first and largest dromaeosaurid known from the Bayan Shireh Formation.
Archaeornithomimus is a genus of ornithomimosaurian theropod dinosaur that lived in Asia during the Late Cretaceous period, around 96 million years ago in the Iren Dabasu Formation.
Bagaceratops is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 72 to 71 million years ago. Bagaceratops remains have been reported from the Barun Goyot Formation and Bayan Mandahu Formation. One specimen may argue the possible presence of Bagaceratops in the Djadochta Formation.
The Bayan Shireh Formation is a geological formation in Mongolia, that dates to the Cretaceous period. It was first described and established by Vasiliev et al. 1959.
Tsagantegia is a genus of medium-sized ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous period. The genus is monotypic, including only the type species, T. longicranialis. The specimen consists of a very partial individual, comprising the skull and lacking postcranial remains. Since it only preserves the skull, Tsagantegia is mainly characterized by its elongated snout and the flattened facial osteoderms, greatly differing from other ankylosaurs.
Talarurus is a genus of ankylosaurid dinosaur that lived in Asia during the Late Cretaceous period, about 96 million to 89 million years ago. The first remains of Talarurus were discovered in 1948 and later described by the Russian paleontologist Evgeny Maleev with the type species T. plicatospineus. It is known from multiple yet sparse specimens, making it one of the most well known ankylosaurines, along with Pinacosaurus. Elements from the specimens consists of various bones from the body; five skulls have been discovered and assigned to the genus, although the first two were very fragmented.
Gilmoreosaurus is the name given to a genus of dinosaur from the Cretaceous of Asia. The type species is Gilmoreosaurus mongoliensis. It is believed to be a hadrosaur or iguanodont from the Iren Dabasu Formation of Inner Mongolia, dating to 96 Ma ago. Additional specimens have been described as distinct species, including G. atavus from the Khodzhakul Formation of Uzbekistan and G. arkhangelskyi from the Bissekty Formation. However, these are based on very fragmentary remains, and their classification is dubious. An additional species, G. kysylkumense is sometimes included, though it has also been referred to the related genus Bactrosaurus.
Erliansaurus is a genus of therizinosaur theropod dinosaur that lived in Asia during the Cenomanian stage of the Late Cretaceous period in what is now Nei Mongol, Iren Dabasu Formation.
Neimongosaurus is a genus of herbivorous therizinosaur theropod dinosaur that lived in Asia during the Cenomanian stage of the Late Cretaceous period in what is now the Iren Dabasu Formation.
Sonidosaurus is a genus of sauropod dinosaur from the Late Cretaceous. It was a titanosaur which lived in what is now Inner Mongolia. The type species, Sonidosaurus saihangaobiensis, was described by Xu, Zhang, Tan, Zhao, and Tan in 2006. It was a small titanosaur, about 9 meters (30 ft) long. It was first discovered in the Saihangaobi, Iren Dabasu (Erlian) Formation, in 2001 in a quarry which would later yield the remains of Gigantoraptor.
The Djadochta Formation 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. Reptile and mammal remains are among the fossils recovered from the formation.
Caenagnathidae is a family of derived caenagnathoid dinosaurs from the Cretaceous of North America and Asia. They are a member of the Oviraptorosauria, and relatives of the Oviraptoridae. Like other oviraptorosaurs, caenagnathids had specialized beaks, long necks, and short tails, and would have been covered in feathers. The relationships of caenagnathids were long a puzzle. The family was originally named by Raymond Martin Sternberg in 1940 as a family of flightless birds. The discovery of skeletons of the related oviraptorids revealed that they were in fact non-avian theropods, and the discovery of more complete caenagnathid remains revealed that Chirostenotes pergracilis, originally named on the basis of a pair of hands, and Citipes elegans, originally thought to be an ornithomimid, named from a foot, were caenagnathids as well.
Gigantoraptor is a genus of large oviraptorosaur dinosaur that lived in Asia during the Late Cretaceous period. It is known from the Iren Dabasu Formation of Inner Mongolia, where the first remains were found in 2005.
The Bayan Mandahu Formation is a geological unit of "redbeds" located near the village of Bayan Mandahu in Inner Mongolia, China, in the Gobi Desert. It dates from the late Cretaceous Period. Laid down in the Campanian, it is dated somewhat uncertainly to between 75 and 71 mya.
The timeline of therizinosaur research is a chronological listing of events in the history of paleontology focused on therizinosaurs. They were unusually long-necked, pot-bellied, and large-clawed herbivorous theropods most closely related to birds. The early history of therizinosaur research occurred in three phases. The first phase was the discovery of scanty and puzzling fossils in Asia by the Central Asiatic Expeditions of the 1920s and Soviet-backed research in the 1950s. This phase resulted in the discovery of the Therizinosaurus cheloniformis type specimen. Soviet paleontologist Evgeny Maleev interpreted these unusual remains as belonging to some kind of gigantic turtle.
Tsagandelta is a genus of deltatheroidean therian mammal that lived in Asia during the Late Cretaceous. Distantly related to modern marsupials, it is part of Deltatheroida, a lineage of carnivorous metatherians common in the Cretaceous of Asia and among the most successful non-theropod carnivores of the region. It represents the first known mammal from the Bayan Shireh Formation.
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