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Ohyamashimo Formation

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Coordinates: 35°06′N 135°06′E / 35.1°N 135.1°E / 35.1; 135.1
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Ohyamashimo Formation
Stratigraphic range: Albian
~112.1–106.4 Ma
TypeGeological formation
Unit ofSasayama Group
UnderliesSawada Formation
OverliesBasement (Unconformity)
Thickness1300 metres
Lithology
PrimaryConglomerate, Sandstone, Mudstone
OtherTuff
Location
Coordinates35°06′N 135°06′E / 35.1°N 135.1°E / 35.1; 135.1
Approximate paleocoordinates47°54′N 132°48′E / 47.9°N 132.8°E / 47.9; 132.8
RegionHyogo prefecture
Country Japan
Type section
Named forOhyamashimo, Tamba-Sasayama
Named byHayashi et al., 2017[1]
Ohyamashimo Formation is located in Japan
Ohyamashimo Formation
Ohyamashimo Formation (Japan)

The Ohyamashimo Formation(大山下層) is an Early Cretaceous (Albian) geologic formation in Japan. It has been dated to the early-mid Albian, between 112.1 ± 0.4 Ma and 106.4 ± 0.4 Ma. Dinosaur remains have been discovered from this formation, including the sauropod Tambatitanis, the theropod Hypnovenator and the ceratopsian Sasayamagnomus. Other representative fossils from the formation include the monstersaurian lizard Morohasaurus and eutherian mammal Sasayamamylos. The depositional environment represents a fluvial system with a subhumid to semi-arid climate.

Fossil content

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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.

Dinosaurs

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Ceratopsians

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Ceratopsians of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Sasayamagnomus[2] S. saegusai Tamba-Sasayama Albian Skull elements and partial postcranial remains. A neoceratopcian; closely related to Aquilops americanus.

Ornithopods

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Ornithopods of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Iguanodontia Indet. Indeterminate Tamba-Sasayama Albian Dental remains.

Sauropods

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Sauropods of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Tambatitanis[3] T. amicitiae Tamba-Sasayama Albian A single partial skeleton. A titanosauriform sauropod

Theropods

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Theropods of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Dromaeosauridae Indet. Indeterminate Tamba-Sasayama Albian Dental remains.
Hypnovenator[4] H. matsubaraetoheorum Tamba-Sasayama Albian A single partial skeleton. A troodontid theropod; closely related to Gobivenator mongoliensis.
Therizinosauria Indet. Indeterminate Tamba-Sasayama Albian Dental remains.
Tyrannosauroidea Indet. Indeterminate Tamba-Sasayama Albian Dental remains.

Thyreophorans

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Thyreophorans of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Ankylosauria Indet. Indeterminate Tamba-Sasayama Albian Dental remains.

Squamates

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Squamtes of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Morohasaurus[5] M. kamitakiensis Tamba-Sasayama Albian A nearly complete left dentary. A monstersaurian lizard
Pachygenys[6] P. adachii Tamba-Sasayama Albian A single, partially broken right mandible A scincomorphan lizard

Amphibians

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Amphibian of the Ohyamashimo Formation[7]
Genus Species Location Stratigraphic position Material Notes Images
Hyogobatrachus H. wadai Tamba-Sasayama Albian A nearly complete skeleton. A frog
Tambabatrachus T. kawazu Tamba-Sasayama Albian An articulated skeleton lacking the anterior part of the skull, most of the pectoral girdle, manus, and feet. A frog

Mammals

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Mammals of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Sasayamamylos[8] S. kawaii Tamba-Sasayama Albian Three dentaries. A asioryctitherian eutherian

Crustaceans

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Crustaceans of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Mongolocypris M. sp. Tamba-Sasayama Albian A ostracod
Conchostraca Indet. Indeterminate Tamba-Sasayama Albian

Molluscs

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Bivalves

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Bivalves of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Sphaerium S. coreanicum Tamba-Sasayama Albian A bivalve

Gastropods

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Gastropods of the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Viviparus V. cf. keishoensis Tamba-Sasayama Albian A gastropod

Oofossils

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Eggs of the Ohyamasimo Formation[9][10]
Genus Species Location Stratigraphic position Material Notes Images
Elongatoolithus E. sp.
Himeoolithus H. murakamii
Nipponoolithus N. ramosus
Prismatoolithus P. sp.
Subtiliolithus S. hyogoensis

References

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  1. ^ Hayashi, Keiichi; Fujita, Saki; Koarai, Kazuto; Matsukawa, Masaki (2017-09-15). "Stratigraphy and paleoenvironment of the Cretaceous Sasayama Group in the Sasayama area, Hyogo Prefecture, western Japan". The Journal of the Geological Society of Japan. 123 (9): 747–764. doi:10.5575/geosoc.2017.0016. ISSN 0016-7630.
  2. ^ Tanaka, Tomonori; Chiba, Kentaro; Ikeda, Tadahiro; Ryan, Michael J. (September 2024). "A new neoceratopsian (Ornithischia, Ceratopsia) from the Lower Cretaceous Ohyamashimo Formation (Albian), southwestern Japan". Papers in Palaeontology. 10 (5). doi:10.1002/spp2.1587.
  3. ^ Saegusa, Haruo; Ikeda, Tadahiro (12 August 2014). "A new titanosauriform sauropod (Dinosauria: Saurischia) from the Lower Cretaceous of Hyogo, Japan". Zootaxa. 3848 (1). doi:10.11646/zootaxa.3848.1.1.
  4. ^ Kubota, Katsuhiro; Kobayashi, Yoshitsugu; Ikeda, Tadahiro (25 July 2024). "Early Cretaceous troodontine troodontid (Dinosauria: Theropoda) from the Ohyamashimo Formation of Japan reveals the early evolution of Troodontinae". Scientific Reports. 14 (1). doi:10.1038/s41598-024-66815-2. PMC 11272788.
  5. ^ Ikeda, Tadahiro; Ota, Hidetoshi; Tanaka, Tomonori; Ikuno, Kenji; Kubota, Katsuhiro; Tanaka, Kohei; Saegusa, Haruo (February 2022). "A fossil Monstersauria (Squamata: Anguimorpha) from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan". Cretaceous Research. 130: 105063. doi:10.1016/j.cretres.2021.105063.
  6. ^ Ikeda, Tadahiro; Ota, Hidetoshi; Saegusa, Haruo (2 January 2015). "A new fossil lizard from the Lower Cretaceous Sasayama Group of Hyogo Prefecture, western Honshu, Japan". Journal of Vertebrate Paleontology. 35 (1): e885032. doi:10.1080/02724634.2014.885032.
  7. ^ Ikeda, Tadahiro; Ota, Hidetoshi; Matsui, Masafumi (June 2016). "New fossil anurans from the Lower Cretaceous Sasayama Group of Hyogo Prefecture, Western Honshu, Japan". Cretaceous Research. 61: 108–123. doi:10.1016/j.cretres.2015.12.024.
  8. ^ Kusuhashi, Nao; Tsutsumi, Yukiyasu; Saegusa, Haruo; Horie, Kenji; Ikeda, Tadahiro; Yokoyama, Kazumi; Shiraishi, Kazuyuki (22 May 2013). "A new Early Cretaceous eutherian mammal from the Sasayama Group, Hyogo, Japan". Proceedings of the Royal Society B: Biological Sciences. 280 (1759): 20130142. doi:10.1098/rspb.2013.0142. PMC 3619506.
  9. ^ Tanaka, Kohei; Zelenitsky, Darla K.; Saegusa, Haruo; Ikeda, Tadahiro; DeBuhr, Christopher L.; Therrien, François (January 2016). "Dinosaur eggshell assemblage from Japan reveals unknown diversity of small theropods". Cretaceous Research. 57: 350–363. doi:10.1016/j.cretres.2015.06.002.
  10. ^ Tanaka, Kohei; Zelenitsky, Darla K.; Therrien, François; Ikeda, Tadahiro; Kubota, Katsuhiro; Saegusa, Haruo; Tanaka, Tomonori; Ikuno, Kenji (October 2020). "Exceptionally small theropod eggs from the Lower Cretaceous Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan". Cretaceous Research. 114: 104519. doi:10.1016/j.cretres.2020.104519.
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