# 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.

## 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 | 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 | 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 |
| Dromaeosauridae Indet. | Indeterminate | Tamba-Sasayama | Albian | Dental remains. | |
| Hypnovenator | 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 | M. kamitakiensis | Tamba-Sasayama | Albian | A nearly complete left dentary. | A monstersaurian lizard | |
| Pachygenys | P. adachii | 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 | 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 | 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 :
| Genus | Species |
| Elongatoolithus | E. sp. |
| Himeoolithus | H. murakamii |
| Nipponoolithus | N. ramosus |
| Prismatoolithus | P. sp. |
| Subtiliolithus | S. hyogoensis |