The Kitadani Dinosaur Quarry Bonebed I, where an outcrop of the Kitadani Formation can be found; the white arrow indicates the location of the type locality of Tyrannomimus fukuiensis. Photographed in c. 2023.
The Kitadani Formation (Japanese: 北谷層Kitadani-sō) is a unit of Lower Cretaceous sedimentary rock which crops out near the city of Katsuyama in Fukui Prefecture, 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]
The Kitadani Formation is a unit within the Tetori Group, a major sequence of Lower Cretaceous rocks that is distributed across Fukui, Ishikawa, and Gifuprefectures of western-central Honshu. The Tetori Group exhibits marked lateral variation, and the Kitadani Formation is only present in Fukui Prefecture.[1] The Kitadani Formation comprises interbedded tuffs, sandstones, and shales and reaches a maximum thickness of approximately one hundred meters (~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.
The formations present within the Tetori Group vary laterally, and the Kitadani Formation crops out only in the Kuzuryū River district of Fukui Prefecture. In this region, the sequence comprises, in ascending stratigraphic order: Gomijima Formation, the Kuwajima Formation, the Akaiwa Formation, and Kitadani Formation.[1] 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 [ja] 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 palaeoclimate during the deposition of the formation was noticeably warmer and drier than that of the older Kuwajima and Okurodani Formations, as evidenced by oxygen isotope records as well as by the presence of crocodylomorph fossils in the former in contrast to their absence in the latter.[6]
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 bivalveNippononaia 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, crocodylomorphs, 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]
Phylogenetic analysis suggests that it a basal member of the group similar in position to Siamosuchus and Sunosuchus.[24]
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]
^ abcdefghiKusuhashi, 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.
^ abWeishampel, 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. ISBN0-520-24209-2.
^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.
^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.
^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. S2CID129324272.
^Fujita, M. (2003). "Geological age of the vertebrate-bearing horizons in the Tetori Group". Memoirs of the Fukui Prefectural Dinosaur Museum. 2: 3–14.
^Yabe, A.; Terada, K.; Sekido, S. (2003). "The Tetori-type flora, revisited: a review". Memoir of the Fukui Prefectural Dinosaur Museum. 2: 23–42.
^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 (3): 201–229. doi:10.2517/1342-8144-17.3.201. S2CID129603779.
^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.
^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.
^ abAzuma Y. 2003. Early Cretaceous vertebrate remains from Katsuyama City, Fukui Prefecture, Japan. Mem Fukui Prefect Dinosaur Mus. 2:17–21.
^T. Tsubamoto, G. W. Rougier, S. Isaji, M. Manabe, and A. M. Forasiepi. 2004. New Early Cretaceous spalacotheriid "symmetrodont" mammal from Japan. Acta Palaeontologica Polonica 49(3):329-346
^ abMiyata, Kazunori; Azuma, Yoichi; Shibata, Masateru (17 February 2016). "New mammalian specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan". Historical Biology. 28 (1–2): 139–150. Bibcode:2016HBio...28..139M. doi:10.1080/08912963.2015.1012509.
^Sonoda Teppei, Azuma Yoichi, Hirayama Ren, Ando Hisao. (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
^Hirayama, Ren. (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.
^Kobayashi, Yoshitsugu (1998). "A new goniopholid from the Early Cretaceous Kitadani Formation, Fukui Prefecture, Japan". Journal of Vertebrate Paleontology. 18 (3): 56A.
^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
^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. Bibcode:2010AcGlS..84..454A. doi:10.1111/j.1755-6724.2010.00268.x.
^ abImai, Takuya; Azuma, Yoichi; Tsukiji, Yuta (2018). "Description of bird tracks from the Kitadani Formation (Aptian), Katsuyama, Fukui, Japan with three-dimensional imaging techniques". Memoir of the Fukui Prefectural Dinosaur Museum. 17 (1–8).
^ abcdeTsukiji, Yuta; Azuma, Yoichi; Shiraishi, Fumito; Shibata, Masateru (May 2019). "A diverse theropod footprint assemblage from the Lower Cretaceous Kitadani Formation, Tetori Group, central Japan". Cretaceous Research. 97: 16–33. Bibcode:2019CrRes..97...16T. doi:10.1016/j.cretres.2019.01.003.