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, 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]

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	35.1°N 135.1°E / 35.1; 135.1
Approximate paleocoordinates	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)

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

Ankylosaurs

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

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
Sauropoda Indet.	Indeterminate	Tamba-Sasayama	Albia
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.

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		A clam shrimp

Molluscs

Bivalves

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

Gastropods

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