Моңғолстандағы Баян Ширех формациясы

Geological formation in Mongolia

The Bayan Shireh Formation (also known as Baynshiree/Baynshire, Baynshirenskaya Svita or Baysheen Shireh) is a geological formation in Mongolia, that dates to the Cretaceous period. It was first described and established by Vasiliev et al. 1959.

The Bayan Shireh Formation is primarily composed by varicoloured claystones and sandstones with calcareous concretions and characterized by grey mudstones and yellowish brown medium grained sandstones. Up to thick, the most complete sections are found in the eastern Gobi Desert, consisting of fine grained, often cross stratified gray sandstone interbedded with claystone and concretionary, intraformational conglomerates with relatively thick units of red to brown mudstone in the upper part. The Baynshire and Burkhant localities are mainly composed by mudstone, siltstone, sandstone, and conglomerates, with most of their sedimentation being fluvial. largescale cross stratification in many of the sandstone layers at the Baynshire locality seem to indicate that a large meandering fluvial system was present. It has been implied that during the late Bayan Shirehnian times, large rivers with direct connections to the sea drained a prominent part of the eastern Gobi region.

According to Jerzykiewicz and Russell, the Bayan Shireh Formation can be divided into 2 informal units: upper and lower beds. While the lower beds are composed by extensive conglomerate that indicates the ancient presence of very active rivers, the upper beds are mainly composed by mudstone and claystone that is interbedded by sandstone, indicating again, the presence of rivers but also lakes and other water bodies. However, examination of the magnetostratigraphy of the formation indicates that the entire Bayan Shireh lies within the Cretaceous Long Normal, which lasted only until the end of the Santonian stage, giving a possible Cenomanian through Late Santonian age, between 98 and 83 million years ago.

Genus Species Location Stratigraphic Position Material Notes Images Deinonychosauria indet. Indeterminate Shine Us Khuduk "Isolated remains including a pedal phalanx II 2." Maleevus M. disparoserratus Sheeregeen GashoonUpper beds "Partial maxillae and a referred braincase." An ankylosaurid now regarded as nomen dubium. Talarurus T. plicatospineus Bayshin Tsav, Baynshire, Shine Us Khuduk "Multiple specimens including partial to nearly complete skulls and postcranial remains." An ankylosaurid. Tsagantegia T. longicranialis Tsagan Teg "Skull lacking lower jaws." A neoceratopsian originally identified as Microceratus. Unnamed neoceratopsian Indeterminate Bayshin Tsav "Left maxilla and teeth." A neoceratopsian.

Dromaeosaurids reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Achillobator A. giganticus Burkhant "Maxilla and fragmentary postcrania." A giant dromaeosaurid. Dromaeosauridae indet. Indeterminate Burkhant "Claw and large postcranial remains." A dromaeosaurid. Unnamed velociraptorine Indeterminate Shine Us Khuduk, Tel Ulan Chaltsai "Fragmentary crania and postcrania from two specimens." A dromaeosaurid.

Hadrosaurs reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Amblydactylus spp. Indeterminate Baynshire "Five three toed footprints." Ornithopod tracks. Gobihadros G. mongoliensis Bayshin Tsav, Baynshire, Char Teeg, Khongil Tsav, Khoorai Tsav Upper beds "Multiple specimens with a virtually complete skull and postcranial remains". A hadrosauroid. Hadrosauroidea indet. Indeterminate Shine Us Khuduk "Isolated surangular". Eggs probably laid by a hadrosaur. Spheroolithus sp. Indeterminate Sheeregeen Gashoon "Egg clutch." Eggs probably laid by a hadrosaur. Undescribed Hadrosauroidea Indeterminate Amtgai, Bayshin Tsav, Bayshin Tsav IV, Khoorai Tsav "Multiple postcranial remains including an articulated skeleton." A hadrosauroid distinct from Gobihadros.

Ornithomimosaurs reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images "Gallimimus" "G. mongoliensis" Bayshin Tsav "Complete skull with postcrania only lacking the caudal region." An informally named ornithomimid that actually differs from Gallimimus. Garudimimus G. brevipes Bayshin Tsav "Skull with fragmented postcrania." An ornithomimosaur. Undescribed ornithomimosaur Indeterminate Amtgai "Nearly long ulna." A large ornithomimosaur. Undescribed ornithomimosaurs Indeterminate Baynshire, Bayshin Tsav, Khongil Tsav, Sheeregeen Gashoon, Shine Us Khuduk "More than five specimens and a bonebed containing mainly postcranial elements." Multiple ornithomimosaurian taxa.

Oviraptorosaurs reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Caenagnathoidea indet. Indeterminate Baynshire "Nests including elongatoolithid eggs and associated juveniles." A large caenagnathoid nesting site. Macroelongatoolithus indet. Indeterminate Baynshire "Eggs within a large nest." Eggs probably laid by a large oviraptorosaur. Unnamed caenagnathid Indeterminate Tsagan Teg "Partial lower jaw similar to Gigantoraptor." A large caenagnathid.

Pachycephalosaurs reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Amtocephale A. gobiensis Amtgai "Nearly complete frontoparietal dome." A primitive pachycephalosaurid.

Sauropods reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Erketu E. ellisoni Bor Guvé "Vertebrae and postcrania." A somphospondylan. Sauropoda indet. Indeterminate Amtgai "Partial vertebrae and pelvic elements." Sauropod tracks. Unnamed titanosaur IndeterminateBor Guvé "Vertebrae." A titanosaur.

Therizinosaurs reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Dendroolithidae spp. Indeterminate Baynshire "Various nests and egg clutches." Eggs probably laid by a therizinosaur Enigmosaurus E. mongoliensis Khara Khutul "Incompletely preserved pelvis." A therizinosauroid. Erlikosaurus E. andrewsi Bayshin Tsav Upper beds "Skull, right pes, and left humerus." A two fingered therizinosaur.

Troodontids reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Undescribed troodontid Indeterminate Bayshin Tsav "Partial vertebrae, forelimbs and hindlimbs." A troodontid.

Tyrannosaurs reported from the Bayan Shireh Formation Genus Species Location Stratigraphic Position Material Notes Images Alectrosaurus?A. olseni? Bayshin Tsav "Two specimens, fragmentary skull and postcrania." A tyrannosauroid also present in the Iren Dabasu Formation Tyrannosauroidea indet. Indeterminate Tsagan Teg "An isolated nearly complete left frontal." A tyrannosauroid.