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′N135°06′E / 35.1°N 135.1°E / 35.1; 135.1
Approximate paleocoordinates	47°54′N132°48′E / 47.9°N 132.8°E / 47.9; 132.8
Region	Hyōgo Prefecture
Country	Japan
Type section
Named for	Ohyamashimo, Tamba-Sasayama
Named by	Hayashi et al., 2017 [1]
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. The Ohyamashimo Formation was called the 'Lower Formation' of the Sasayama Group before it was named in 2017. ^[1]

Fossil content

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

Ceratopsians

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

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

Sauropods

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

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

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

Squamates

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

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

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

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

Bivalves

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

Gastropods

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

Oofossils

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

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.