The Ohyamashimo Formation(大山下層) is an

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(Albian) geologic formation in

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. It has been dated to the early-mid Albian, between 112.1 ± 0.4 Ma and 106.4 ± 0.4 Ma.

Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

remains have been discovered from this formation, including the sauropod '' Tambatitanis'', the theropod '' Hypnovenator'' and the ceratopsian ''

Sasayamagnomus ''Sasayamagnomus'' (meaning "Gnome from Sasayama") is a genus of neoceratopsian dinosaur from the Early Cretaceous (Albian) Ohyamashimo Formation of Hyogo prefecture, Japan. The genus contains a single species, ''S. saegusai''. Type specimen i ...

''. Other representative fossils from the formation include the monstersaurian lizard ''

Morohasaurus ''Morohasaurus'' is an extinct genus of ''cf.'' monstersaurian squamates know from a single left dentary from the Early Cretaceous (?Albian) Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan. The type and only ...

'' and

eutherian Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distingu ...

mammal '' Sasayamamylos''. The

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...

represents a

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

system with a subhumid to

semi-arid A semi-arid climate, semi-desert climate, or steppe climate is a aridity, dry climate sub-type. It is located on regions that receive precipitation below Evapotranspiration#Potential evapotranspiration, potential evapotranspiration, but not as l ...

climate. The Ohyamashimo Formation was called the 'Lower Formation' of the Sasayama Group before it was named in 2017.

Fossil content

Dinosaurs

Ornithischians

Saurischians

= Sauropods

= Theropods

Squamates

Amphibians

Mammals

Crustaceans

Molluscs

Bivalves

Gastropods

Oofossils

{, class="wikitable" align="center" , - ! colspan="7" align="center" ,

Eggs An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

of the Ohyamasimo Formation{{cite journal , last1=Tanaka , first1=Kohei , last2=Zelenitsky , first2=Darla K. , last3=Therrien , first3=François , last4=Ikeda , first4=Tadahiro , last5=Kubota , first5=Katsuhiro , last6=Saegusa , first6=Haruo , last7=Tanaka , first7=Tomonori , last8=Ikuno , first8=Kenji , title=Exceptionally small theropod eggs from the Lower Cretaceous Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan , journal=Cretaceous Research , date=October 2020 , volume=114 , pages=104519 , doi=10.1016/j.cretres.2020.104519 , - ! Genus ! Species ! Location ! Stratigraphic position ! Material ! Notes ! Images , - , '' Elongatoolithus'' , ''E. sp.'' , , , , , , - , '' Himeoolithus'' , ''H. murakamii'' , , , , , , - , '' Nipponoolithus'' , ''N. ramosus'' , , , , , , - , ''

Prismatoolithus ''Prismatoolithus'' is an oogenus of dinosaur egg from the Cretaceous (Hauterivian-Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stag ...

'' , ''P. sp.'' , , , , , , - , '' Subtiliolithus'' , ''S. hyogoensis'' , , , , , , -

References

Geologic formations of Japan Lower Cretaceous Series of Asia Cretaceous Japan Albian Stage