Yezo Group

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Not to be confused with Yeso Group.
Yezo Group
Stratigraphic range: Aptian–Paleocene
Type
Stratigraphic group
Sub-unitsShuparogawa Formation, Maruyama Formation, Hikagenosawa Formation, Saku Formation, Mikasa Formation, Kashima Formation, Haborogawa Formation, Osoushinai Formation, Hakobuchi Formation
UnderliesIshikari Group, Poronai Group, Neogene deposits
OverliesSorachi Group
Thickness10,000 metres (32,810 ft)
Lithology
PrimaryMudstone, sandstone
OtherTuffite, conglomerate
Location
RegionHokkaido
Sakhalin
Country Japan
 Russia

The Yezo Group is a

slope of the ancient Yezo subduction margin. It forms a continuous depositional sequence with the Sorachi Group, which overlies the Horokanai Ophiolite. The sequence gradually shallows upwards with the terminal Hakobuchi Formation representing a fluvial-inner shelf environment.[2]

Numerous fossils are known from the unit, mostly ammonites and bivalves, but also marine vertebrates such as mosasaurs, plesiosaurs [3] and marine turtles. Dinosaur remains are among the fossils that have been recovered from the group. These include a partial cervical vertebra and right hand from the therizinosaurid Paralitherizinosaurus, from Early Campanian Osoushinai Formation from northern Hokkaido.[4][5] Nipponosaurus is known from an unnamed unit of the group from Southern Sakhalin, probably late Santonian or early Campanian in age.[6] Kamuysaurus, which is known from the early Maastrichtian Hakobuchi Formation of southern Hokkaido, was also discovered in layers of this group.[7]

Fossil content

Reptiles

Reptiles reported from the Yezo Group
Genus Species Presence Material Notes Images
Anomalochelys A. angulata Hobetsu-cho, Hokkaido. (Cenomanian)[8] A
nanhsiungchelyid
.
Chupkaornis C. keraorum Kashima Formation (Coniacian to Santonian).[9] A
hesperornithiform
.
Kamuysaurus K. japonicus Hakobuchi Formation.[7] "A nearly complete skeleton with the skull and mandible (HMG-1219)".[7] A hadrosaur.
Mesodermochelys M. undulatus Hakobuchi Formation[10] and upper part of the Osoushinai Formation.[11] -NMV-3, a proximal half of right humerus (Osoushinai Formation) .[11] A dermochelyid turtle.
M. sp. Osoushinai Formation.[12] A carapace with boreholes likely made by bivalves, and associated with many mollusc remains.[12] A dermochelyid turtle.
Mosasaurus M. hobetsuensis Hakobuchi Formation.[13] A mosasaurine mosasaur.
Nipponosaurus N. sachalinensis Sakhalin.[6][14] A hadrosaur.
Paralitherizinosaurus P. japonicus Osoushinai Formation.[4] Partial vertebra and partial right hand.[4] A therizinosaur.
Phosphorosaurus P. ponpetelegans Hakobuchi Formation.[13] A well-preserved skull with some associated vertebrae. A halisaurine mosasaur with proportionately large eyes and binocular vision.
Pliosauridae gen. et. sp. indet. Indeterminate Cenomanian to Turonian localities in Hokkaido.[15] 4 indeterminate remains.[15] Pliosaur remains, some with skull sizes comparable to Megacephalosaurus.
Taniwhasaurus T. sp. Kashima Formation.[16] A fragmentary skull, not diagnostic to the species level. A tylosaurine mosasaur also known from New Zealand, Antarctica, and South Africa; originally informally named 'Yezosaurus mikasaensis'.

Fish

Fish reported from the Yezo Group
Genus Species Presence Material Notes Images
Apsopelix A. miyazakii Nakagawa Town[17] and Mikasa area,[18] Hokkaido (Turonian). 2 specimens. A
crossognathid
.

Echinoderms

Echinoderms reported from the Yezo Group
Genus Species Presence Material Notes Images
?Austinocrinus ?A. sp. Unknown locality, possibly in south-central Hokkaido, thought to be Santonian-Campanian.[19] "One nodal and two pluricolumnals, associated on a bedding plane, so probably from a single individual".[19] A crinoid.
?Balanocrinus ?B. sp. Upper Coniacian-Campanian portions of the Haborogawa Formation).[19] One pluricolumnal.[19] A crinoid.
Isocrinus I. sp. Haborogawa Formation (upper Turonian-Coniacian).[19] One pluricolumnal.[19] A crinoid.
Isselicrinus I. sp. Campanian upper Yezo Group.[19] One pluricolumnal and five very poorly preserved columnals.[19]

Molluscs

Molluscs reported from the Yezo Group
Genus Species Presence Material Notes Images
?Abyssochrysoidea Osoushinai Formation.[12] A single specimen found associated with the remains of a Mesodermochelys sp.[12] A gastropod.
Bivalvia Unidentified.[12] Osoushinai Formation.[12] A single specimen found associated with the remains of a Mesodermochelys sp.[12]
?Cephalaspidea Osoushinai Formation.[12] A single specimen found associated with the remains of a Mesodermochelys sp.[12] A gastropod.
Cheloniceras C. sp. Tsukenai Formation (Aptian).[20] An
ammonite
.
Colombiceras C. spathi Tsukenai Formation (Aptian).[20] An
ammonite
.
Gaudryceras G. denseplicatum Satonosawa Creek, Hokkaido (middle Turonian).[21] An ammonoid.
?Gyrodes ?G. sp. Osoushinai Formation.[12] A single specimen found associated with the remains of a Mesodermochelys sp.[12]
Haboroteuthis H. poseidon Upper Haborogawa Formation (Upper Santonian).[22] "KMNH IvP 902,002, a lower jaw."[22] A
teuthid
.
Hikidea H. cf. yasukawensis Osoushinai Formation.[12] A single specimen found associated with the remains of a Mesodermochelys sp.[12]
Inoceramus I. (Sphenoceramus) orientalis Uppermost Haborogawa Formation (middle-upper part of the lower Campanian).[23] A bivalve.
I. (Sphenoceramus) schmidti Uppermost Haborogawa Formation (middle-upper part of the lower Campanian).[23] A bivalve.
I. teshioensis Gakkonosawa Creek, Hokkaido (late Turonian).[21] Disarticulated valves.[21] A bivalve.
Nanaimoteuthis N. hikidai Uppermost Haborogawa Formation (lower Campanian).[22] "KMNH IvP 902,001, a lower jaw, the only specimen available."[22] A vampyromorph.
N. jeletzkyi Hokkaido (Santonian to lower Campanian.)[24] A vampyromorph.
N. yokotai Satonosawa Creek and Gakkonosawa Creek, Hokkaido (middle and late Turonian).[21] Jaw fossils. A vampyromorph.
Paleocirroteuthis P. sp. Hokkaido (Santonian to lower Campanian).[24] A
cirroctopodid
.
Provanna P. cf. nakagawensis Osoushinai Formation.[12] 3 specimens found associated with the remains of a Mesodermochelys sp.[12] An abyssochrysoid gastropod.
Rhytidoplites R. adkinsi Tsukenai Formation (Aptian).[20] An
ammonite
.
Scalarites S. mihoensis Gakkonosawa Creek, Hokkaido (late Turonian).[21] An ammonoid.
S. scalaris Satonosawa Creek, Hokkaido (middle Turonian).[21] An ammonoid.
Tetragonites T. glabrus Satonosawa Creek, Hokkaido (middle Turonian).[21] An ammonoid.
Thyasira T. tanabei Osoushinai Formation.[12] 2 articulated specimens found associated with the remains of a Mesodermochelys sp.[12] A bivalve.
Yezoteuthis Y. giganteus Osoushinai Formation.[25] Jaw fossils. A very large oegopsid.

Paleoflora

Plants reported from the Yezo Group
Genus Species Presence Material Notes Images
Eydeia E. hokkaidoensis Haborogawa Formation (Coniacian-Santonian).[26] 5
perimineralized fruits.[26]
 A cornale similar to the extant Davidia involucrata.
Mikasapteris M. rothwellii Mikasa Locality.[27] A
pinnule.[27]
 A probable stem polypodioid leptosporangiate fern.
Mukawastrobus M. satoi Hakobuchi Formation.[28] "A single cylindrical
seed cone 2 cm long, 1.1 cm wide."[28]
 A cypress.
Nilssonia N. yezoensis Hakobuchi Formation.[29] A cycad.
Obirafructus O. kokubunii Haborogawa Formation (Coniacian to Santonian).[30] "A
permineralized reproductive axis bearing at least 42 spirally arranged follicles."[30]
 A saxifragale.
Stockeystrobus S. interdigitata Hoborogawa Formation (Coniacian to Santonian).[31] A seed cone.[31] A sequoioid.
Zamites Z. bayeri Kashima Formation (Coniacian).[32] A bennettitale.

See also

  • List of dinosaur-bearing rock formations

References

  1. ^ Shigeta, Yasunari; Maeda, Haruyoshi (2005). "Yezo Group Research in Sakhalin—A Historical Review" (PDF). The Cretaceous System in the Makarov Area, Southern Sakhalin, Russian Far East. 31. National Science Museum Monographs: 1–24.
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  8. ^ Ren Hirayama; Kazuhiko Sakurai; Tsutomu Chitoku; Gentaro Kawakami; Norio Kito (2001). "Anomalochelys angulata, an unusual land turtle of family Nanhsiungchelyidae (Superfamily Treionychoidea; Order Testudines) from the Upper Cretaceous of Hokkaido, North Japan". Russian Journal of Herpetology. 8 (2): 127–138. Archived from the original on 2011-08-26.
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    .
  11. ^ a b Hirayama, Ren; Hikida, Yoshinori (March 1998). "Mesodermochelys (Testudines; Chelonioidea; Dermochelyidae) from the Late Cretaceous of Nakagawa-cho, Hokkaido, North Japan". Bulletin of the Nakagawa Museum of Natural History. 1: 69 to 76.
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  22. ^ a b c d "Late Cretaceous record of large soft-bodied coleoids based on lower jaw remains from Hokkaido, Japan - Acta Palaeontologica Polonica". www.app.pan.pl. Retrieved 2022-08-18.
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  30. ^ a b Kajita, Yui; Suzuki, Mayumi Hanari; Nishida, Harufumi (May 2020). "A Multicarpellary Apocarpous Gynoecium from the Late Cretaceous (Coniacian–Santonian) of the Upper Yezo Group of Obira, Hokkaido, Japan: Obirafructus kokubunii gen. & sp. nov". Acta Phytotaxonomica et Geobotanica. 72 (1): 1–21.
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