# Kuwajima Formation

The Kuwajima Formation is an Early Cretaceous geologic formation in Japan. Its precise age is uncertain due to a lack of identifying fossils, and it was previously considered likely Valanginian to Hauterivian in age. However, it is now considered to probably be Barremian in age. Dinosaurs and other vertebrates has been recovered from the Kaseki-kabe "Fossil-bluff" locality in the uppermost part of the formation.
The multituberculate mammals Hakusanobaatar matsuoi and Tedoribaatar reini are known from the Kuwajima Formation. A member of Tritylodontidae, Montirictus kuwajimaensis, has also been recovered from the unit.

## Vertebrate Paleobiota

After Matsuoka et al. (2002)

### Fish

Fish reported from the Kuwajima Formation :
| Genus | Species | Material | Notes |
| Sinamia | S. kukurihime | Mostly complete skeleton | An amiiform fish related to bowfins |
| Tetoriichthys | T. kuwajimaensis | | The oldest record of Osteoglossiform |
| Lepidotes | L. sp. | | |
| Pachycormidae | Indeterminate | Jaw | |

### Amphibians

Amphibians reported from the Kuwajima Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Shirerpeton | S. isajii | Kaseki-kabe | Facies III | Partial disarticulated skull | Albanerpetontid | |
| Anura | Indeterminate | | | Isolated longbone, as well as a partial skeleton "composed of a few skull elements and several postcranial bones, including the femur, ilium, and vertebrae" | Partial skeleton belongs to a basal frog that lies outside of Neobatrachia. | |

### Choristoderes

Choristoderes reported from the Kuwajima Formation :
| Genus | Species | Location | Stratigraphic position | Notes | Images |
| Monjurosuchus | Indeterminate | Kaseki-kabe | Facies III | | Monjurosuchus |
| Neochoristodera | Indeterminate | | Facies I | The first report of a neochoristodere from Japan | Monjurosuchus |
| Choristodera | Indeterminate | Kaseki-kabe | Facies III | | Monjurosuchus |

### Squamates

Squamates reported from the Kuwajima Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Asagaolacerta | A. tricuspidens | Kaseki-kabe | Facies III | "An association of skull, jaws and postcranial bones of a small lizard with facetted tricuspid teeth, possibly a right maxilla" | | Kaganaias |
| Hakuseps | H. imberis | Kaseki-kabe | Facies III | An almost complete left dentary | | Kaganaias |
| Kaganaias | K. hakusanensis | Kaseki-kabe | Facies III | "Part and counterpart of articulated partial skeleton comprising parts of the dors. vert. series and parts of the tail, pelvis, and hind limbs" | | Kaganaias |
| Kuroyuriella | K. mikikoi | Kaseki-kabe | Facies III | "A disarticulated skull on four originally conjoined blocks, an association on two small blocks" | | Kaganaias |
| Kuwajimalla | K. kagaensis | Kaseki-kabe | Facies III | | | Kaganaias |
| Sakurasaurus | Indeterminate | Kaseki-kabe | Facies III | "Small block with disarticulated association of skull bones, vertebrae, ribs, pelvis and hindlimb bones" | | Kaganaias |
| Paramacellodidae | Indeterminate | Kaseki-kabe | Facies III | | | Kaganaias |
| Squamata | Indeterminate | Kaseki-kabe | Facies III | | Five distinct taxa | Kaganaias |

### Dinosaurs

Dinosaurs reported from the Kuwajima Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Albalophosaurus | A. yamaguchiorum | Kaseki-kabe | Facies III | Partial skull and lower jaws | |
| Dromaeosauridae | Indeterminate | Kaseki-kabe | Facies III | | |
| Enantiornithes | Indeterminate | Kaseki-kabe | Facies III | | |
| Ornithischia | Indeterminate | | | Right dentary, left maxilla, isolated teeth | Distinct from Albalophosaurus |
| Sauropoda ("Oharasisaurus") | Indeterminate | Kaseki-kabe | Facies III | | Tooth |
| Styracosterna | Indeterminate | | | Maxillary and dental teeth | |

### Other reptiles

Choristoderes reported from the Kuwajima Formation :
| Genus | Species | Location |
| Trionychidae | Indeterminate | Kaseki-kabe |
| Testudinoidea | Indeterminate | Kaseki-kabe |
| Sinemydidae | Indeterminate | Kaseki-kabe |
| Ornithocheiridae | Indeterminate | Kaseki-kabe |
| Gnathosaurinae | Indeterminate | Kaseki-kabe |
| Dsungaripteroidea? | Indeterminate | Kaseki-kabe |

### Mammaliamorphs

Mammaliamorphs reported from the Kuwajima Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Hakusanobaatar | H. matsuoi | Kaseki-kabe | Facies III | Dentary fragments and teeth | Eobaatarid |
| Hakusanodon | H. archaeus | Kaseki-kabe | Facies III | | Eutriconodont |
| Montirictus | M. kuwajimaensis | Kaseki-kabe | Facies III | | Tritylodontid |
| Tedoribaatar | T. reini | Kaseki-kabe | Facies III | "Fragment of right lower jaw with p4" | Eobaatarid |
| Multituberculata | Indeterminate | Kaseki-kabe | Facies III | | |

## Invertebrate Paleobiota

Invertebrates reported from the Kuwajima Formation :
| Genus | Species | Location | Notes |
| Nipponoridium | B. matsuoi | Kaseki-Kabe | Mimarachnid hemipteran |
| Nipponohagla | N. kaga | Kaseki-Kabe | Prophalangopsid |
| Kagapsychops | K. araneus | Kaseki-Kabe | Psychopsid |
| Coleoptera | Indeterminate | Kaseki-Kabe | |
| Unio | U. ogamigoensis | Kaseki-Kabe | Unionid |
| Sphaerium | S. sp. | Kaseki-Kabe | Sphaeriid |
| Viviparus | V. onogoensis | Kaseki-Kabe | Viviparid |
| Micromelania | M.? katoensis | Kaseki-Kabe | Sphaeriid |
| Physidae | Indeterminate, two species | Kaseki-Kabe | |
| Pupilloidea | Indeterminate | Kaseki-Kabe | |