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

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.

Re-examination of the cranial osteology of the Arctic Alaskan hadrosaurine with implications for its taxonomic status

“…Phylogenetic analyses were conducted based on the most recent hadrosauroid data matrix by Kobayashi et al [43]. In addition to the PCF hadrosaurine, two OTUs (Operational Taxonomic Unit) of immature Edmontosaurus annectens (AMNH FARB 5046, an articulated partial skull; and disarticulated juvenile specimens at the Royal Ontario Museum: list of specimens in S2 Table) were added to the data matrix.…”

“…In addition to the PCF hadrosaurine, two OTUs (Operational Taxonomic Unit) of immature Edmontosaurus annectens (AMNH FARB 5046, an articulated partial skull; and disarticulated juvenile specimens at the Royal Ontario Museum: list of specimens in S2 Table) were added to the data matrix. Four new characters were added to the character list of Kobayashi et al [43] (S1 Text). The updated data matrix comprises 73 OTUs and 354 equally-weighed, unordered characters (S1 Data).…”

“…Edmontosaurus annectens (e.g., ROM 57100), Edmontosaurus regalis (e.g., AMNH FARB 5254), Kamuysaurus japonicus [43], and Kerberosaurus manakini [59,60]. The ventral flange is approximately 1.24 times the height of the posterior constriction ventral to the infratemporal fenestra, and the posterior constriction is approximately 0.64 times the height of the length between the ventral apexes of the orbit and the infratemporal fenestra (UAMES 4187, UAMES 7336).…”

“…process of the prefrontal, as in members of Edmontosaurini (except Kamuysaurus japonicus [43]). The entire posterior margin of the frontal is rugose for contact with the parietals.…”

“…The tooth crowns are diamond-shaped and the available specimens show variant height/width ratios ranging from 2.04-2.33. The tooth crowns bear one primary ridge and a secondary ridge in some teeth (mesial to the primary ridge, if present) on its lingual enameled surface as in some Edmontosaurus regalis (present in a few teeth of CMN 2289) and lambeosaurines [53,75]. The primary ridge on the dentary teeth is positioned at the midline of the tooth crown and is slightly sinuous.…”