The Yezo Group is a

stratigraphic group In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into superg ...

Hokkaido is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...

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 ...

and

Sakhalin Sakhalin ( rus, Сахали́н, p=səxɐˈlʲin) is an island in Northeast Asia. Its north coast lies off the southeastern coast of Khabarovsk Krai in Russia, while its southern tip lies north of the Japanese island of Hokkaido. An islan ...

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

which is primarily

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

in age (

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

to Earliest

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

). It is exposed as roughly north–south trending belt extending 1,500 kilometres through central Hokkaido from

Urakawa is a List of towns in Japan, town located in Hidaka Subprefecture, Hokkaido, Japan. As of 1 October 2020, the town has an estimated population of 12,074 and a population density, density of 17 persons per km2. The total area is 694.24 km2. ...

Cape Sōya is the northernmost point of the island of Hokkaidō, Japan. It is situated in Wakkanai, Hokkaido, Wakkanai, Sōya Subprefecture. The is at the cape, although the true List of extreme points of Japan, northernmost point under Japanese control ...

and Sakhalin from the south coast to

Alexandrovsk-Sakhalinsky District Alexandrovsk-Sakhalinsky District () is an administrative district (raion) of Sakhalin Oblast, Russia, one of the seventeen in the oblast.Law #25-ZO As a municipal division, it is incorporated as Alexandrovsk-Sakhalinsky Urban Okrug.Law #524 It i ...

. It consists of marine

forearc basin A forearc is a region in a subduction zone between an oceanic trench and the associated volcanic arc. Forearc regions are present along convergent margins and eponymously form 'in front of' the volcanic arcs that are characteristic of convergent ...

sediments, typically

turbiditic A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. ...

and bioturbated mudstones and sandstones with subordinate conglomerate primarily deposited on the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

and

slope In mathematics, the slope or gradient of a Line (mathematics), line is a number that describes the direction (geometry), direction of the line on a plane (geometry), plane. Often denoted by the letter ''m'', slope is calculated as the ratio of t ...

of the ancient Yezo subduction margin. It forms a continuous depositional sequence with the Sorachi Group, which overlies the Horokanai

Ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

. The sequence gradually shallows upwards with the terminal Hakobuchi Formation representing a fluvial-inner shelf environment. Numerous fossils are known from the unit, mostly ammonites and bivalves, but also marine vertebrates such as mosasaurs, plesiosaurs and marine turtles. Dinosaur remains are among the fossils that have been recovered from the group. These include a partial

cervical vertebra In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sauropsid s ...

and right hand from the

therizinosaurid Therizinosauridae (meaning 'scythe lizards')Translated paper
is an extinct family of derive ...

Paralitherizinosaurus ''Paralitherizinosaurus'' is an extinct genus of therizinosaurid theropod dinosaurs from the Late Cretaceous Osoushinai Formation of Hokkaido, Japan. The genus contains a single species, ''Paralitherizinosaurus japonicus'', known from a partial ...

'', from Early

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

Osoushinai Formation from northern Hokkaido. ''

Nipponosaurus ''Nipponosaurus'' (meaning "Japanese lizard") is a Lambeosaurinae, lambeosaurine hadrosaur from sediments of the Yezo Group, in Sinegorsk on the island of Sakhalin, which was part of Japan at the time of the species' classification. The type sp ...

'' is known from an unnamed unit of the group from Southern Sakhalin, probably late

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...

or early Campanian in age.Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, Asia)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 593-600. '' Kamuysaurus'', which is known from the early

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

Hakobuchi Formation of southern

, was also discovered in layers of this group.

Fossil content

Reptiles

Fish

Echinoderms

Molluscs

Paleoflora

References

{{coord missing, Hokkaidō Prefecture Geologic groups of Asia Geologic formations of Japan Geologic formations of Russia Lower Cretaceous Series of Asia Aptian Stage Albian Stage Upper Cretaceous Series of Asia Cenomanian Stage Turonian Stage Coniacian Stage Santonian Stage Campanian Stage Maastrichtian Stage Cretaceous–Paleogene boundary Paleogene System of Asia Danian Stage Mudstone groups Sandstone groups Tuff groups Conglomerate groups Paleontology in Japan Paleontology in Russia