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| Kamuysaurus japonicus
Kobayashi, Nishimura, Takasaki, Chiba, Fiorillo, Tanaka, Chinzorig, Sato & Sakurai, 2019
Illustration: Masato Hattori marchan-forest.blogspot.com
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Abstract
A nearly complete skeleton of a new hadrosaurid, Kamuysaurus japonicus gen. et sp. nov., was discovered from the outer shelf deposits of the Upper Cretaceous Hakobuchi Formation of the Yezo Group in Hobetsu area of Mukawa town in Hokkaido, Japan. Kamuysaurus belongs to the sub-clade of Hadrosaurinae, Edmontosaurini, and forms a monophyly with Laiyangosaurus and Kerberosaurus from the northern Far East. Kamuysaurus has a long anterior platform for the nasofrontal sutural surface, which may indicate the presence of a small supracranial crest, similar to a sub-adult form of Brachylophosaurus based on the extension of the nasofrontal sutural surface. The Dispersal Extinction Cladogenesis analysis with the 50% Majority Rule consensus tree suggests that the clade of Kamuysaurus, Laiyangosaurus, and Kerberosaurus may have dispersed into Asia prior to the late Campanian and the potential endemism of this clade during the late Campanian and early Maastrichtian in the northern Far East. The results of both Dispersal Extinction Cladogenesis and Ancestral State Reconstruction analyses imply that the marine-influenced environment in North America during the Campanian may have played an important role for the hadrosaurid diversification in its early evolutionary history.
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| Figure 2: Selected skull elements of Kamuysaurus japonicus gen. et sp. nov. (a) Right jugal in lateral view (reversed); (b) right maxilla in lateral view (reversed); (c) prefrontals, frontals, and postorbitals in dorsal view; (d) squamosal, exoccipital, basioccipital, and basisphenoid in posterior view; (e) left squamosal in lateral view; (f), right quadratojugal in lateral view (reversed); (g) left pterygoid in lateral view; (h) left quadrate in lateral view; (i) maxillary tooth in labial and distal views; (j) dentary tooth in lingual and distal views; (k) right dentary in lateral view (reversed); (l) right surangular in lateral view (reserved); (m) right ceratobranchial in lateral view (reversed). All scales are 5 cm except 1 cm scale bar for (i,j).
Abbreviations: acp, ascending process; ap, anterior process; bo, basioccipital; cp, coronoid process; ectr, ectopterygoid ramus; exo, exoccipital; fm, foramen magnum; fr, frontal; pf, prefrontal; po, postorbital; pop, postcotyloid process; pr, primary ridge; prp, precotyloid process; ptp, pterygoid process; ptw, pterygoid wing; qjn, quadratojugal notch; rap, retroarticular process; sp, sutural platform; sq, squamosal. Grey areas are missing parts.
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| Figure 3: (a) The holotype skeleton of Kamuysaurus japonicus gen. et sp. nov. (b) Reconstructed skeleton, showing recovered elements. Selected postcranial elements: cervical vertebrae (atlas, axis, and fourth and twelfth cervicals) in left lateral view (c), dorsal vertebrae (first, seventh, and sixteenth dorsals) in left lateral view (d), caudal vertebrae (anterior, middle, and posterior caudals) in left lateral view (e), left scapula (f) and coracoid (g) in lateral view, right sternum in ventral view (h), left humerus in anterior view (i), right ulna and radius in medial view (j), right manus in dorsal view (k), right pelvis in lateral view (l), right femur in anterior view (m), right tibia in anterior view (n), right fibula in lateral view (o), right astragalus and calcaneum, articulated positioned with tibia (p), and right pes in dorsal view (q). All scales are 10 cm except 1 m scale for (b).
Abbreviations; ac, acromion process; ast, astragalus; cal, calcaneum; dpc, deltopectoral crest; fi, fibula; icg, intercondylar groove; il, ilium; is, ischium; ltr, lesser trochanter; mc2, metacarpal II; mc5, metacarpal V; mt2, metatarsal II; mt4, metatarsal IV; nc, neurocentrum; od, odontoid; olp, olecranon process; pc, pleurocentrum; pu, pubis; ra, radius; ti, tibia; ul, ulna; vp, ventral process.
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Systematic paleontology
Dinosauria (Owen, 1842)
Ornithischia (Seeley, 1887)
Ornithopoda (Marsh, 1881)
Hadrosauridae (Cope, 1870)
Hadrosaurinae (Lambe, 1918)
Kamuysaurus japonicus gen. et sp. nov.
Etymology: “Kamuy” refers deity to the Ainu, which is indigenous people in Hokkaido Island of Japan, and “sauros” means reptile in Latin. Specific name, “japon”, refers to Japan.
Holotype: A nearly complete skeleton with the skull and mandible (HMG-1219), housed at the Hobetsu Museum, Hobetsu area of Mukawa town, Hokkaido, Japan.
Locality and horizon: An outcrop (42° 50′ 48″N, 142° 7′ 20″E) along the Shirafunezawa Creek in the northern Hobetsu area of Mukawa town in Hokkaido; the middle of IVb unit (early Maastrichtian) of the Hakobuchi Formation of the Yezo Group.
Diagnosis: This specimen is assigned as a hadrosaurine hadrosaurid with the following unique characters: the midpoint of the quadratojugal notch positioned at roughly three-quarters of the total length of the quadrate from the dorsal end, short ascending process of the surangular, and anterior inclination of neural spines of sixth to thirteenth dorsal vertebrae. Diagnosed also by the unique combination of characters: slightly curved primary ridge of the maxillary teeth, high average height/width ratio of dentary tooth over 3.30, moderate medial extension of the symphyseal process of the dentary, anterior margin of the coronoid process of the dentary more developed than the posterior margin, triangular ventral margin of the anterior process of the jugal as wide as its height, moderately inclined palatine articular facet of the jugal, nearly straight caudal margin of the quadratojugal flange of the jugal, smoothly curved anterodorsal margin of the prefrontal along the orbital rim, squamosal process of the postorbital terminates anterior to the quadrate cotylus, long nasofrontal sutural surface of the frontal, subrectangular infratemporal fenestra, weak expansion of deltopectoral crest of the humerus, and slender humerus with humeral shaft less than 20% as wide as the length.
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| Figure 5: (a) A strict consensus tree of the most parsimonious trees obtained in this analysis. Numbers above branch lines represent bootstrap proportions, whereas those below the lines represent Bremer decay values. Bootstrap proportions lower than 20 and Bremer decay values less than 1 are not shown. Synapomorphies at each node is shown in Supplementary Text S2. (b) Time-calibrated cladogram with the 50% Majority Rule consensus tree of Hadrosaurinae, calculated based on additive method, showing ancestral ranges of all nodes inferred by the Dispersal Extinction Cladogenesis analysis in this study. Results using other time-calibration methods are provided in Supplementary Fig. S28. |
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| Life reconstruction of Kamuysaurus japonicus gen. et sp. nov. with a carcass of a mosasaur (Phosphorosaurus ponpetelegans), a sea turtle (Mesodermochelys undulates), and shells of ammonoids (Patagiosites compressus and Gaudryceras hobetsense) and bivalves (Nannonavis elongatus) on the beach (above). The individual of Kamuysaurus in the foreground is reconstructed based on the assumption of the presence of a supracranial crest, similar to a sub-adult form of Brachylophosaurus. The individual behind it is reconstructed without the crest.
Illustration: Masato Hattori marchan-forest.blogspot.com
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| Carcass of Kamuysaurus, floating in the sea, with two mosasaurs (Mosasaurus hobetsuensis), two sea turtles (Mesodermochelys undulates), and four ammonoids (Pachydiscus japonicus).
Illustration: Masato Hattori marchan-forest.blogspot.com
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Yoshitsugu Kobayashi, Tomohiro Nishimura, Ryuji Takasaki, Kentaro Chiba, Anthony R. Fiorillo, Kohei Tanaka, Tsogtbaatar Chinzorig, Tamaki Sato and Kazuhiko Sakurai. 2019. A New Hadrosaurine (Dinosauria: Hadrosauridae) from the Marine Deposits of the Late Cretaceous Hakobuchi Formation, Yezo Group, Japan. Scientific Reports. 9(1); 1–14. DOI: 10.1038/s41598-019-48607-1
