Kitadani Formation

The Kitadani Formation (Japanese: 北谷層, romanized: Kitadani-sō) is a unit of Lower Cretaceous sedimentary rock which crops out near the city of Katsuyama in the Fukui Prefecture of Japan, and it is the primary source of Cretaceous-aged non-marine vertebrate fossils in Japan. Dinosaur remains are among the fossils that have been recovered from the formation, but it also preserves a diverse assemblage of plants, invertebrates, and other vertebrates.[2] Most, if not all, of the fossil specimens collected from the Kitadani Formation are reposited at the Fukui Prefectural Dinosaur Museum.[3]

Kitadani Formation
Stratigraphic range: Barremian-Aptian
~125–115 Ma
TypeGeological formation
Unit ofTetori Group
UnderliesOmichidani Formation
OverliesAkaiwa Formation
Thickness~100 m (330 ft)[1]
Lithology
PrimaryTuff, sandstone, shale
OtherCoal
Location
Coordinates36.1°N 136.6°E / 36.1; 136.6
Approximate paleocoordinates47.3°N 137.7°E / 47.3; 137.7
Region Fukui Prefecture
Country Japan
Type section
Named byUnknown[1]
Kitadani Formation (Japan)

The Kitadani Formation is a unit within the Tetori Group, a major sequence of Lower Cretaceous rocks which is distributed across the Fukui, Ishikawa, and Gifu prefectures of western-central Honshu, Japan. The Tetori Group exhibits marked lateral variation, and the Kitadani Formation is only present in the Fukui Prefecture.[1] The Kitadani Formation comprises interbedded tuffs, sandstones, and shales and reaches a maximum thickness of approximately 100 m (~328 feet).[1] It conformably overlies the Akaiwa Formation and is unconformably overlain by the Omichidani Formation.[4] The Kitadani Formation is significant because it is the major source of dinosaur fossils in Japan and because of Japan's unique position along the northeastern margin of Eurasia during the Early Cretaceous.

Geology

The Kitadani Formation is a unit within the Tetori Group, a Lower Cretaceous sequence of predominantly sedimentary rock which crops out in the Fukui, Ishikawa, and Gifu prefectures of west-central Honshu, Japan in the region surrounding Mount Haku.[1][5]

The formations present within the Tetori Group vary laterally, and the Kitadani Formation crops out only in the Kuzuryū River district of the Fukui Prefecture. In this region, the sequence comprises, in ascending stratigraphic order, Gomijima Formation, the Kuwajima Formation, the Akaiwa Formation and Kitadani Formation.[1] Here, the Kitadani Formation comprises alternating horizons of red-brown tuffs, blackish shales and sandstones, and thin coal beds. The sandstones within the Kitadani Formation are light gray and green and range in clast size from fine to coarse. The type section of the Kitadani Formation occurs along the Nakanomatadani branch of the Takinami River[6] near the city of Katsuyama, where it is approximately 100 m (~328 feet) in thickness. The Kitadani Formation conformably overlies the Akaiwa Formation and is unconformably overlain by the Omichidani Formation.[1]

The Kitadani Formation has had varying nomenclature throughout the history of its study.[1] In the early stratigraphic literature on the Tetori Group, the Kitadani Formation was variably referred to as the "Lower part of the Omichidani Formation",[7] the "Chinaboradani Alternation of Tuff, Shale, and Sandstone",[8] the "Kitadani Alternation of Sandstone, Shale, and Tuff",[9] and simply the "Kitadani Alternation"[10] prior to its designation as a formation.[1]

Age

The Kitadani Formation was biostratigraphically dated to the late Barremian and early Aptian ages of the Early Cretaceous Epoch in 2002 based upon the presence of the freshwater bivalve Nippononaia ryosekiana.[11] In 2005, part of the Kitadani Formation was biostratigraphically dated to the Barremian Age based upon the occurrence of the charophyte gyrogonite Clavator harrisii reyi in association with other charophytes.[12] These biostratigraphic age assignments are supported by zircon fission track radioisotopic ages of tuff, which date the Kitadani Formation to 127-115 Ma.[13]

Fossil assemblage

The Kitadani Formation preserves a diverse assemblage of plant fossils; invertebrate fossils; and vertebrate body and trace fossils, including mammals, turtles, neosuchian reptiles, and dinosaurs. Many vertebrate specimens from the Kitadani Formation are incomplete and poorly preserved, so taxonomic diversity is likely higher than it seems.

Plant fossils

The plant fossil assemblage of the Kitadani Formation is characterized by a rarity of ferns and an abundance of cycadales and conifers represented mostly by cones and shoots.[14] A palynological study in 2013 resulted in the identification of greater than 40 species of spores, pollen grains, and plant fragments from the Kitadani Formation representing gymnosperms, freshwater algae, and epiphyllous fungus; however, no angiosperm pollen was identified.[15] Branches of the conifer Brachyphyllum obesum have been recovered, which was interpreted to represent the warming and possible drying of the climate toward the upper Tetori Group.[16] This interpretation is supported by the lack of plants from lower in the Tetori Group, such as ginkgos, in the Kitadani Formation.[17]

Invertebrate fossils

The invertebrate fossil assemblage of the Kitadani Formation mostly comprises freshwater and brackish water bivalve and gastropod mollusks.[18]

Mammalia

At least three mammalian taxa have been recovered from the Kitadani Formation, represented by rare teeth and partial jaws. In 2004, the spalacotheriid "symmetrodont" Symmetrolestes parvus was reported based upon a fragmentary right mandible with the first incisor and five postcanine teeth preserved.[19] Two non-therian mammal specimens were reported in 2015, including an eobaatarid multituberculate and a triconodontid eutriconodontan.[20] These specimens were noted as possessing non-tribosphenic dentition, and were interpreted being taxonomically distinct to closely related taxa from elsewhere in the Tetori Group, but neither specimen was named. The eobaatarid is represented only by a damaged left premolar. The triconodontid is represented by a partial right dentary possessing a faint Meckelian groove.

Mammaliaformes reported from the Kitadani Formation
Genus Species Location Stratigraphic position Material Notes Images
Symmetrolestes S. parvus North of Dinosaur Quarry Fragmentary right mandible Spalacotheriid
Eobaataridae Indeterminate Dinosaur Quarry Bonebed I A left p4 crown
?Triconodontidae Indeterminate Dinosaur Quarry Bonebed I "a fragment of possible right dentary with a damaged molariform crown and roots"

Testudines

Turtles are represented mostly by shell fragments within the Kitadani Formation.[21][22] In 2002, a preliminary evaluation of fragmentary specimens resulted in the identification of the taxa Adocus, Basilemys, and Trionychidae. A more recent evaluation of all 700+ turtle specimens from the Kitadani Formation was conducted in 2015. In that study, the authors concluded that the turtle assemblage of the Kitadani Formation consists of four trionychoid taxa and two other eucryptodires. In addition to the genera reported in 2002, Perochelys, Gobiapalone, Apalonina, and an unnamed nanhsiungchelyid were identified.

Eusuchia

A nearly complete skeleton of a goniopholidid eusuchian has been noted from the Kitadani Formation, but this material remains formally unpublished and unnamed.[23] This specimen was discovered in 1982, and it was hypothesized to be closely related to Sunosuchus, Goniopholis, and Eutretauranosuchus based on a preliminary phylogenetic analysis.

Dinosauria

Dinosaurs are among the most well-known vertebrate taxa from the Kitadani Formation. Taxa from all three major dinosaurian clades—Theropoda, Sauropodomorpha, and Ornithischia—have been recovered.[2]

Among theropods, two taxa have been named, with additional indeterminate dromaeosaurid and other theropod material also preserved. Fukuiraptor kitadanensis was reported in 2000 based upon a partial skull and associated partial postcranium.[24] The phylogenetic relationships of Fukuiraptor are uncertain. Although confidently assigned to the Megaraptora, various phylogenetic analyses have suggested that megaraptorans may either be allosauroids, tyrannosauroids or non-tyrannosauroid coelurosaurs.[25] Fukuivenator paradoxus was reported in 2016, and it is interpreted to be an early-diverging maniraptoran.[26] However, its unique combination of ancestral and derived features associated with several different coelurosaurian clades precludes referral to a more exclusive clade than Maniraptora.

The titanosaurian sauropod dinosaur Fukuititan nipponensis was reported from the Kitadani Formation in 2010 based upon a single partial skeleton including cranial and postcranial material.[27] Other indeterminate sauropod material is also preserved.[2]

Ornithischian dinosaurs are represented in the Kitadani Formation by two named taxa and other indeterminate specimens, including an unnamed psittacosaurid ceratopsian.[2] Fukuisaurus tetoriensis was named in 2003 based upon sparse cranial material, but more complete specimens have been recovered in the time since.[28] Fukuisaurus is interpreted to be a non-hadrosauroid hadrosauriform.[29] Another hadrosauriform Koshisaurus katsuyama was reported in 2015 and interpreted to be an early-branching hadrosauroid, not especially closely related to Fukuisaurus.[29]

Additionally, non-avialan theropod, avialan theropod, sauropod, ornithischian tracks have been reported from the Kitadani Formation.[2]

Dinosaur egg fragments have also been reported from the Kitadani Formation, including Plagioolithus fukuensis, a three-layered eggshell interpreted as a fossil avian egg. If indeed avian, Plagioolithus would represent the oldest known fossil bird egg.[30]

Dinosaurs reported from the Kitadani Formation
Genus Species Location Stratigraphic position Material Notes Images
Fukuiraptor F. kitadaniensis Kitadani Dinosaur Quarry Bonebed I Partial skeleton with paratypes Basal Megaraptoran

Fukuisaurus F. tetoriensis Kitadani Dinosaur Quarry Bonebed I Multiple specimens representing a partial skeleton Hadrosauroid
Fukuititan F. nipponensis Kitadani Dinosaur Quarry Bonebed II Associated partial skeleton Titanosauriform
Fukuivenator F. paradoxus Kitadani Dinosaur Quarry Partial skeleton with skull Basal maniraptoriform

Koshisaurus K. katsuyama Kitadani Dinosaur Quarry Bonebed IV Hadrosauroid

Fukuipteryx[31] F. prima Kitadani Dinosaur Quarry (unspecified) Associated disarticulated partial skeleton Avialan

See also
  • List of dinosaur-bearing rock formations

References
  1. Kusuhashi, N.; Matsuoka, H.; Kamiya, H.; Setoguchi, T. (2002). "Stratigraphy of the late Mesozoic Tetori Group in the Hakusan Region, central Japan : an overview". Memoirs of the Faculty of Science, Kyoto University. Series of Geology and Mineralogy. 59 (1): 9–31.
  2. Weishampel, D.B.; et al. (2004). "Dinosaur distribution (Early Cretaceous, Asia)." In: Weishampel, D.B.; Dodson, P.; and Osmólska, H. (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 563-570. ISBN 0-520-24209-2.
  3. http://www.dinosaur.pref.fukui.jp/en/
  4. Tsubamoto, T.; Rougier, G.W.; Isaji, S.; Manabe, M.; Forasiepi, A.M. (2004). "New Early Cretaceous spalacotheriid "symmetrodont" mammal from Japan". Acta Palaeontologica Polonica. 49 (3): 329–346.
  5. Yamada, Toshihiro; Sano, Shin-ichi (2018). "Designation of the Type Section of the Tetori Group and Redefinition of the Kuzuryu Group distributed in Central Japan". Memoir of the Fukui Prefectural Dinosaur Museum. 17: 89–94.
  6. ja:滝波川
  7. Maeda, S. (1953). "The Mesozoic in north of Katsuyama, Fukui Prefecture". Journal of the Geological Society of Japan. 59: 323–324.
  8. Maeda, S. (1957). "Stratigraphy and geological structure of the Tetori Group along the Uchinami and Itoshiro rivers". Journal of the Geological Society of Japan. 63: 357–365. doi:10.5575/geosoc.63.357.
  9. Maeda, S. (1958). "Stratigraphy and geological structure of the Tetori Group in the Hakusan district (Part 1. Stratigrphy)". Journal of the Geological Society of Japan. 64 (758): 583–594. doi:10.5575/geosoc.64.583.
  10. Maeda, S. (1961). "On the geological history of the Mesozoic Tetori Group in Japan". Journal of College of Arts and Sciences, Chiba University. 3: 396–426.
  11. Kozai, T.; Ishida, K.; Park, S.O.; Chang, K.H. (2002). "Early Cretaceous non-marine bivalves from Korea and Japan". Abstracts of the 2002 Meeting of the Palaeontological Society of Japan: 16–17.
  12. Kubota, K. (2005). "Charophyte gyrogonites from the Lower Cretaceous Kitadani Formation of the Tetori Group in the Takinamigawa area, Katsuyama City, Fukui Prefecture, central Japan". Paleontological Research. 9 (2): 203–213. doi:10.2517/prpsj.9.203.
  13. Fujita, M. (2003). "Geological age of the vertebrate-bearing horizons in the Tetori Group". Memoirs of the Fukui Prefectural Dinosaur Museum. 2: 3–14.
  14. Yabe, A.; Terada, K.; Sekido, S. (2003). "The Tetori-type flora, revisited: a review". Memoir of the Fukui Prefectural Dinosaur Museum. 2: 23–42.
  15. Legrand, J.; Pons, D.; Terada, K.; Yabe, A.; Nishida, H. (2013). "Lower Cretaceous (Upper Barremian-Lower Aptian?) palynoflora from the Kitadani Formation (Tetori Group, Inner Zone of Central Japan)". Paleontological Research. 17: 201–229. doi:10.2517/1342-8144-17.3.201.
  16. Yabe, A.; Kubota, K. (2004). "Brachyphyllum obesum, newly discovered thermophilic conifer branch from the Lower Cretaceous Kitadani Formation of the Tetori Group, central Japan". Memoir of the Fukui Prefectural Dinosaur Museum. 3: 23–29.
  17. Suzuki, S. Shibata; Azuma, Y.; Yukawa, H.; Sekiya, T.; Masaoka, Y. (2015). "Sedimentary environment of dinosaur fossil bearing successions of the Lower Cretaceous Kitadani Formation, Tetori Group, Katsuyama City, Fukui, Japan". Memoir of the Fukui Prefectural Dinosaur Museum. 14: 1–9.
  18. Azuma Y. 2003. Early Cretaceous vertebrate remains from Katsuyama City, Fukui Prefecture, Japan. Mem Fukui Prefect Dinosaur Mus. 2:17–21.
  19. Tsubamoto, T.; Rougier, G. W.; Isaji, S.; Manabe, M.; Forasiepi, A. M. (2004). "New Early Cretaceous spalacotheriid "symmetrodont" mammal from Japan". Acta Palaeontologica Polonica. 49 (3): 329–346.
  20. Miyata, Kazunori; Azuma, Yoichi; Shibata, Masateru (2015). "New mammalian specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan". Historical Biology. 28 (1–2): 139–150. doi:10.1080/08912963.2015.1012509.
  21. Sonoda T, Azuma Y, Hirayama R, Ando H. (2015) New trionychoid specimens and turtle fauna from the Lower Cretaceous Kitadani Formation of the Tetori Group in central Japan. PeerJ PrePrints 3:e949v1 https://doi.org/10.7287/peerj.preprints.949v1
  22. Hirayama, R. (2002) Preliminary report of the fossil turtles from the Kitadani Formation (Early Cretaceous) of the Tetori Group of Katsuyama, Fukui Prefecture, Central Japan. Memoirs of the Fukui Prefectural Dinosaur Museum. 1: 29-40.
  23. Kobayashi, Y (1998). "A new goniopholid from the Early Cretaceous Kitadani Formation, Fukui Prefecture, Japan". Journal of Vertebrate Paleontology. 18 (3): 56A.
  24. Currie, P.J.; Azuma, Y. (2006). "New specimens, including a growth series, of Fukuiraptor (Dinosauria, Theropoda) from the Lower Cretaceous Kitadani Quarry of Japan". J. Paleont. Soc. Korea. 22 (1): 173–193
  25. Apesteguía, Sebastián; Smith, Nathan D.; Valieri, Rubén Juárez; Makovicky, Peter J. (2016). "An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina". PLOS ONE. 11 (7): e0157793. doi:10.1371/journal.pone.0157793.
  26. Azuma, Y.; Xu, X.; Shibata, M.; Kawabe, S.; Miyata, K.; Imai, T. (2016). "A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians". Scientific Reports. 6: 20478. doi:10.1038/srep20478. PMC 4763874. PMID 26908367.
  27. Azuma, Y.; Shibata, M. (2010). "Fukuititan nipponensis, a new titanosauriform sauropod from the Early Cretaceous Tetori Group of Fukui Prefecture, Japan". Acta Geologica Sinica – English Edition. 84 (3): 454–462.
  28. Kobayashi, Y.; Azuma, Y. (2003). "A new iguanodontian (Dinosauria; Ornithopoda), form the lower Cretaceous Kitadani Formation of Fukui Prefecture, Japan". Journal of Vertebrate Paleontology. 23 (1): 166–175. doi:10.1671/0272-4634(2003)23[166:anidof]2.0.co;2.
  29. Shibaba, Masateru; Azuma, Yoichi (2015). "New basal hadrosauroid (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation, Fukui, central Japan" (PDF). Zootaxa. 3914 (4): 421–40. doi:10.11646/zootaxa.3914.4.3. PMID 25661952.|
  30. Imai, Takuya; Azuma, Yoichi (2015). "The oldest known avian eggshells, Plagioolithus fukuiensis, from the Lower Cretaceous (upper Barremian) Kitadani Formation, Fukui, Japan". Historical Biology. 27 (8): 1090–1097. doi:10.1080/08912963.2014.934232.
  31. Imai, Takuya; Azuma, Yoichi; Kawabe, Soichiro; Shibata, Masateru; Miyata, Kazunori; Wang, Min; Zhou, Zhonghe (December 2019). "An unusual bird (Theropoda, Avialae) from the Early Cretaceous of Japan suggests complex evolutionary history of basal birds". Communications Biology. 2 (1): 399. doi:10.1038/s42003-019-0639-4. ISSN 2399-3642. PMC 6856171. PMID 31754639.
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