''Yamatosaurus'' (meaning " Yamato reptile") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of basal hadrosaurid from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...

(

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interv ...

)-aged Kita-Ama Formation of Awaji Island, Japan. The genus contains a single

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

, ''Yamatosaurus izanagii''.

Discovery and naming

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

MNHAH D1-033516, consisting of part of the right lower jaw, twelve

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

, four

cervical vertebrae In tetrapods, cervical vertebrae (singular: 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 ...

, three

cervical ribs A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of th ...

, a partial right coracoid and a posterior caudal vertebra, was discovered on Awaji Island in Japan in May 2004 by Shingo Kishimoto. In 2005, the find was reported in the scientific literature.Suzuki, D., Saegusa, H. & Furutani, H. 2005. "Newly found hadrosaur fossil co-producing broadleaf fossils from Sumoto, west central Japan". ''Journal of Vertebrate Paleontology'' 25: 120A Kishimoto in 2013 donated the holotype to Japan's Museum of Nature and Human Activities in the Hyogo Prefecture, where the fossils were prepared by Kazumi Wada, Tomomi Ikeda and Chisato Ota to be described in 2021. The species ''Yamatosaurus izanagii'' was named in 2021 by Yoshitsugu Kobayashi, Ryuji Takasaki, Katsuhiro Kubota and Anthony Ricardo Fiorillo. The fossils were found in dark grey mudstones within the upper part Kita-Ama Formation, which was deposited in marine conditions in distal turbidite facies on the edge of the

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...

in an

intra-arc basin In geology an intra-arc basin is a sedimentary basin that exists amidst a volcanic arc. Being located next to volcanoes intra-arc basins tend to host Volcano-sedimentary sequences. Cura-Mallín at the border of Chile and Argentina is an example ...

. The sediments date to subchron 32.1r28, corresponding to the early

stage of the Late Cretaceous, around 71.94–71.69 million years ago, making it roughly contemporaneous with fellow Japanese hadrosaur '' Kamuysaurus.'' Yamatosaurus izanagii restoration

Etymology

The generic name, ''Yamatosaurus'', refers to Yamatai, also known as Yamato, an ancient region in Japan ruled by the

Yamato Kingdom The is the period of Japanese history when the Imperial court ruled from modern-day Nara Prefecture, then known as Yamato Province. While conventionally assigned to the period 250–710, including both the Kofun period (–538) and the Asuka ...

, while the specific name, ''Y. izanagii'', refers to the deity Izanagi, who created eight islands in Yamato: Awaji Island (where the holotype was discovered)

Shikoku is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), ...

, Oki,

Kyushu is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surroun ...

, Iki,

Tsushima Tsushima may refer to: Places * Tsushima Island, part of Nagasaki Prefecture ** Tsushima, Nagasaki, a city in Nagasaki Prefecture (coterminous with Tsushima Island) ** Tsushima Province, a historical province, coterminous with modern Tsushima Su ...

, Sado and

Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island ...

Classification

''Yamatosaurus'' is a basal hadrosaurid, more derived than ''Hadrosaurus'' but less than Saurolophinae+ Lambeosaurinae. Its presence, along with those of '' Plesiohadros'' and '' Tanius'', suggests East Asia may have served as a refuge for basal hadrosaurs in the Late Cretaceous. However, it was also contemporaneous with the more derived ''Kamuysaurus'', suggesting some level of provinciality.

References

Hadrosaurs Late Cretaceous dinosaurs of Asia Fossil taxa described in 2021 Ornithischian genera {{ornithopod-stub