The Ohyamashimo Formation(大山下層) is a Lower Cretaceous (Albian) geologic formation, distributed in Tamba and Tamba-Sasayama, Hyogo Prefecture, Japan. It has been dated to the early-mid Albian, between 112.1 ± 0.4 Ma and 106.4 ± 0.4 Ma. 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.
Fossil content
Dinosaurs
Ornithischians Ornithischians of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes ImagesAnkylosauria Indet.Indeterminate Kamitaki Bonebed Quarry, TambaAlbianDental remains.Iguanodontia Indet.Indeterminate Kamitaki Bonebed Quarry, TambaAlbianDental remains. Sasayamagnomus S. saegusai Miyada microvertebrate site, Tamba-Sasayama Albian Skull elements and partial postcranial remains. A neoceratopsian; closely related to Aquilops americanus.
Saurischians
Sauropods Sauropods of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes Images Tambatitanis T. amicitiae Kamitaki Bonebed Quarry, Tamba Albian A single partial skeleton. A titanosauriform sauropod
Theropods
Indeterminate theropod dental remains are known from the Kamitaki Bonebed Quarry, Tamba.
Theropods of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes Images Hypnovenator H. matsubaraetoheorum Nishikosa, Tamba-Sasayama Albian A single partial skeleton. A troodontid theropod; closely related to Gobivenator mongoliensis. Therizinosauria Indet. Indeterminate Kamitaki Bonebed Quarry, Tamba Albian Dental remains. Tyrannosauroidea Indet. Indeterminate Kamitaki Bonebed Quarry, Tamba Albian Dental remains.
Squamates Squamtes of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes Images Morohasaurus M. kamitakiensis Kamitaki Egg Quarry, Tamba Albian A nearly complete left dentary. A monstersaurian lizard Pachygenys P. adachii Miyada microvertebrate site, Tamba-Sasayama Albian A single, partially broken right mandible A scincomorphan lizard
Amphibians Amphibian of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes Images Hyogobatrachus H. wadai Kamitaki Bonebed Quarry, Tamba Albian A nearly complete skeleton. A frog Tambabatrachus T. kawazu Kamitaki Bonebed Quarry, Tamba 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 S. kawaii Miyada microvertebrate site, 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. Albian A ostracod Conchostraca Indet. Indeterminate Albian A clam shrimp
Molluscs
Bivalves Bivalves of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes Images Sphaerium S. coreanicum Albian A sphaeriid bivalve
Gastropods Gastropods of the Ohyamashimo Formation Genus Species Location Stratigraphic position Material Notes Images Viviparus V. cf. keishoensis Albian A viviparid gastropod
Oofossils Oofossils of the Ohyamasimo Formation Genus Species Location Stratigraphic position Material Notes Images Elongatoolithus E. sp. Kamitaki Bonebed Quarry, Tamba Likely laid by oviraptorosaur Himeoolithus H. murakamii Kamitaki Egg Quarry, Tamba Likely laid by a small theropod Nipponoolithus N. ramosus Kamitaki Bonebed Quarry and Kamitaki Egg Quarry, Tamba Likely laid by non-avian maniraptoran theropod Prismatoolithus P. sp. Kamitaki Bonebed Quarry and Kamitaki Egg Quarry, Tamba Likely laid by either troodontids or birds Subtiliolithus S. hyogoensis Kamitaki Bonebed Quarry and Kamitaki Egg Quarry, Tamba Likely laid by a small theropod Spheroolithus S. sp. Kamitaki Bonebed Quarry, Tamba Likely laid by hadrosaurs or other ornithopods
References