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Ohyamashimo Formation

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 and the theropod Hypnovenator. 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.

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)

Fossil Records

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Arthropods

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Arthropods reported from the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Mongolocypris M. sp. An ostracod.
Conchostraca indeterminate

Molluscs

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Molluscs reported from the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Viviparus V. cf. keishoensis A gastropod.
Sphaerium S. coreanicum A bivalve.

Amphibians

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Amphibians reported from the Ohyamashimo Formation[2]
Genus Species Location Stratigraphic position Material Notes Images
Hyogobatrachus H. wadai A nearly complete skeleton. Forms a sister group with the Lalagobatrachia.
Tambabatrachus T. kawazu An articulated skeleton lacking the anterior part of the skull, most of the pectoral girdle, manus, and feet.

Mammals

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Mammals reported from the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Sasayamamylos[3] S. kawaii Three dentaries. An asioryctitherian mammal.

Lizards

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Lizards reported from the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Morohasaurus[4] M. kamitakiensis A nearly complete left dentary. A monstersaurian lizard.
Pachygenys[5] P. adachii A single, partially broken right mandible

Dinosaurs

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Dinosaurs reported from the Ohyamashimo Formation
Genus Species Location Stratigraphic position Material Notes Images
Tambatitanis[6] T. amicitiae A single partial skeleton. A titanosauriform sauropod.
 
Tyrannosauroidea Indeterminate Dental remains.
Therizinosauria Indeterminate Dental remains.
Dromaeosauridae Indeterminate Dental remains.
Hypnovenator[7] H. matsubaraetoheorum A single partial skeleton. A troodontid theropod.
Ankylosauria Indeterminate Dental remains.
Iguanodontia Indeterminate Dental remains.
Neoceratopsia Indeterminate Partial skeleton including skull elements.

Oofossils

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Eggs reported from the Ohyamashimo Formation[8][9]
Genus Species Location Stratigraphic position Material Notes Images
Himeoolithus H. murakamii
Subtiliolithus S. hyogoensis
Prismatoolithus P. sp.
Nipponoolithus N. ramosus
Elongatoolithus E. sp.
Spheroolithus S. sp.

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. ^ 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ 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.
  9. ^ 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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