A New Hadrosaurine (Dinosauria: Hadrosauridae) from the Marine Deposits of the Late Cretaceous Hakobuchi Formation, Yezo Group, Japan

Yoshitsugu Kobayashi,Anthony R Fiorillo,Tamaki Sato,Kentaro Chiba,Ryuji Takasaki,Kazuhiko Sakurai,Kohei Tanaka,Tomohiro Nishimura,Tsogtbaatar Chinzorig

doi:10.1038/s41598-019-48607-1

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.

Highlights

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
The Hakobuchi Formation is the uppermost unit of the Yezo Group, which is a part of Cretaceous to Paleocene forearc basin deposits that crop out in the southern Hokkaido, Japan (Fig. 1a,b; Supplementary Text S1 and Figs S1 and S2)[18,19]
The monomolecular model has the lowest value of Akaike information criterion (AIC), but the Von Bertalanffy and Gompertz models have ΔAIC values lower than 2, suggesting these three models have substantial support to be plausible growth models (Supplementary Table S5)

Summary

Introduction

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. This specimen was recovered from the marine deposits of the Late Cretaceous Hakobuchi Formation (early Maastrichtian) of the Yezo Group in Hokkaido, Japan, during the joint excavation of the Hobetsu Museum and Hokkaido University Museum, that largely occurred in 2013 and 2014 This new hadrosaurid contributes to our understanding of the diversity of hadrosaurids in marine-influenced environments because hadrosaurid materials from marine deposits are rarely reported: with notable exceptions such as the lambeosaurine Nipponosaurus from Russia[13], the hadrosaurine Hadrosaurus[14], Lophorhothon[15], and Augustynolophus[16] from USA, and other fragmentary materials[1,17]. This new specimen sheds light on our understanding of the diversity of hadrosaurids in the Far East, and the spatial and environmental significance of hadrosaurid evolution during the Late Cretaceous

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Conclusion