The Kuwajima Formation is an

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. Its precise age is uncertain due to a lack of identifying fossils, and it was previously considered likely

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretaceou ...

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by the Va ...

in age. However, it is now considered to probably be

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...

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 Tritylodontidae ("three-knob teeth", named after the shape of their cheek teeth) is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, bearing several mammalian traits like erect limbs, endothermy and detail ...

, '' Montirictus kuwajimaensis'', has also been recovered from the unit.Hiroshige Matsuoka, Nao Kusuhashi and Ian J. Corfe (2016). "A new Early Cretaceous tritylodontid (Synapsida, Cynodontia, Mammaliamorpha) from the Kuwajima Formation (Tetori Group) of central Japan". Journal of Vertebrate Paleontology. Online edition:

Vertebrate Paleobiota

Fish

Amphibians

Choristoderes

Squamates

Dinosaurs

Mammaliamorphs

Invertebrate Paleobiota

References

Geologic formations of Japan Lower Cretaceous Series of Asia Cretaceous Japan {{coord missing, Japan Barremian Stage