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Ohyamashimo Formation
Ohyamashimo Formation
Stratigraphic range: Albian; ~112.1–106.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Sasayama Group
Underlies	Sawada Formation
Overlies	Basement (Unconformity)
Thickness	1300 metres
Lithology
Primary	Conglomerate, Sandstone, Mudstone
Other	Tuff
Location
Coordinates	35°06′N 135°06′E / 35.1°N 135.1°E
Approximate paleocoordinates	47°54′N 132°48′E / 47.9°N 132.8°E
Region	Hyogo prefecture
Country	Japan
Type section
Named for	Ohyamashimo, Tamba-Sasayama
Named by	Hayashi et al., 2017
	Palaeotaku/sandbox (Japan)

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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.

Fossil Records

Arthropods

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

Molluscs

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

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

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

Lizards

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

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

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.

^ 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.
^ 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.
^ 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.
^ 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.
^ 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.
^ 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.
^ 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.
^ 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.
^ 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.

[SasayamaStrat-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.

[TambaFrog-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.

[Sasayamamylos-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.

[Morohasaurus-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.

[Pachygenys_adachii-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.

[Tambatitanis-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.

[Hypnovenator-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.

[Tambaegg2016-8] 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.

[Tambaegg2020-9] 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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Ohyamashimo Formation
Stratigraphic range: Albian ~112.1–106.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Sasayama Group
Underlies	Sawada Formation
Overlies	Basement (Unconformity)
Thickness	1300 metres
Lithology
Primary	Conglomerate, Sandstone, Mudstone
Other	Tuff
Location
Coordinates	35°06′N 135°06′E / 35.1°N 135.1°E / 35.1; 135.1
Approximate paleocoordinates	47°54′N 132°48′E / 47.9°N 132.8°E / 47.9; 132.8
Region	Hyogo prefecture
Country	Japan
Type section
Named for	Ohyamashimo, Tamba-Sasayama
Named by	Hayashi et al., 2017^[1]
Palaeotaku/sandbox (Japan)