A new basal hadrosaurid (Dinosauria: Ornithischia) from the latest Cretaceous Kita-ama Formation in Japan implies the origin of hadrosaurids

Yoshitsugu Kobayashi,Anthony R Fiorillo,Ryuji Takasaki,Katsuhiro Kubota

doi:10.1038/s41598-021-87719-5

Abstract

Here we describe a partial hadrosaurid skeleton from the marine Maastrichtian Kita-ama Formation in Japan as a new taxon, Yamatosaurus izanagii gen. et sp. nov., based on unique characters in the dentition. Our phylogenetic analysis demonstrates Yamatosaurus izanagii belongs to Hadrosauridae, composed of Hadrosaurus foulkii + (Yamatosaurus izanagii + (Saurolophinae + Lambeosaurinae)). The coracoid lacks a biceps tubercle as in non-hadrosaurid hadrosauroids, suggesting its presence is a key feature for the clade of Saurolophinae and Lambeosaurinae. The evolutionary rates analysis further supports that shoulder and forelimb features, which are likely to have been involved in locomotion, were important for the early evolution of Hadrosauridae. Our biogeographic analyses show that basal hadrosaurids were widely distributed in Asia and Appalachia, that the clade of Saurolophinae and Lambeosaurinae originated in Asia, and that eastern Asia may have served as a refugium of relict hadrosauroid taxa such as Plesiohadros djadokhtaensis, Tanius sinensis, and Yamatosaurus izanagii during the Late Cretaceous. The contemporaneous occurrence of basal (Yamatosaurus izanagii) and derived (Kamuysaurus japonicus) hadrosaurids during the Maastrichtian in Japan is the first record in Asia. Because of the long geographical distance between these localities, they likely did not co-exist, but instead demonstrate some level of provinciality.

Highlights

Hadrosauroids were successful herbivorous ornithischian dinosaurs during the Cretaceous
The exposed beds at the quarry are within subchron 32.1r28, which is currently dated as 71.94–71.69 Ma29, as well as the Nostoceras hetonaiense Zone[22], which is the same as the ammonite zone that includes Kamuysaurus japonicus
The ontogenetic stage of Yamatosaurus izanagii cannot be determined histologically due to the absence of any weight-bearing limb bones

Summary

Introduction

Hadrosauroids were successful herbivorous ornithischian dinosaurs during the Cretaceous. Social behaviors, expressed by their unique supracranial crests, are likely to have contributed to the success of the derived hadrosauroids[16,17,18] In addition to their functional adaptations, Kobayashi et al.[19] recently proposed that occupation of marine-influenced environments by ancestral hadrosaurids played an important role in their early evolution. In addition to these specimens, an amateur fossil collector, Mr Shingo Kishimoto, discovered a partial hadrosauroid specimen in May 2004 This new discovery includes a dentary, a surangular, isolated dentary teeth, cervical vertebrae, a caudal vertebra, cervical ribs, and a coracoid (MNHAH D1-033516).

Methods

Results

Conclusion