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. 2017 Apr 6;12(4):e0175253.
doi: 10.1371/journal.pone.0175253. eCollection 2017.

Supplementary cranial description of the types of Edmontosaurus regalis (Ornithischia: Hadrosauridae), with comments on the phylogenetics and biogeography of Hadrosaurinae

Hai Xing  1 , Jordan C Mallon  2 , Margaret L Currie  2
Affiliations

Supplementary cranial description of the types of Edmontosaurus regalis (Ornithischia: Hadrosauridae), with comments on the phylogenetics and biogeography of Hadrosaurinae

Hai Xing et al. PLoS One. .

Abstract

The cranial anatomy of the flat-skulled hadrosaurine Edmontosaurus regalis (Ornithischia: Hadrosauridae) is extensively described here, based on the holotype and paratype collected from the middle part of the Horseshoe Canyon Formation in southern Alberta. Focus is given to previously undocumented features of ontogenetic and phylogenetic importance. This description facilitates overall osteological comparisons between E. regalis and other hadrosaurids (especially E. annectens), and revises the diagnosis of E. regalis, to which a new autapomorphy (the dorsal half of the jugal anterior process bearing a sharp posterolateral projection into the orbit) is added. We consider the recently named Ugrunaaluk kuukpikensis from the upper Campanian/lower Maastrichtian of Alaska a nomen dubium, and conservatively regard the Alaskan material as belonging to Edmontosaurus sp.. A phylogenetic analysis of Hadrosauroidea using maximum parsimony further corroborates the sister-taxon relationship between E. regalis and E. annectens. In the strict consensus tree, Hadrosaurus foulkii occurs firmly within the clade comprising all non-lambeosaurine hadrosaurids, supporting the taxonomic scheme that divides Hadrosauridae into Hadrosaurinae and Lambeosaurinae. Within Edmontosaurini, Kerberosaurus is posited as the sister taxon to the clade of Shantungosaurus + Edmontosaurus. The biogeographic reconstruction of Hadrosaurinae in light of the time-calibrated cladogram and probability calculation of ancestral areas for all internal nodes reveals a significantly high probability for the North American origin of the clade. However, the Laramidia-Appalachia dispersals around the Santonian-Campanian boundary, inferred from the biogeographic scenario for the North American origin of Hadrosaurinae, are in conflict with currently accepted paleogeographic models. By contrast, the Asian origin of Hadrosaurinae with its relatively low probability resulting from the biogeographic analysis is worth seriously considering, despite the lack of fossil material from the Santonian and lower Campanian of Asia. Extra fossil collecting in appropriate geographic locations and stratigraphic intervals of Asia and Europe will help to clarify the biogeographic dynamics of hadrosaurine dinosaurs in the near future.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Geographic and stratigraphic distribution of Edmontosaurus regalis in Alberta (modified from [8, 17]).
A, map of southern Alberta; the grey rectangle highlights the central region of the Red Deer River valley, where E. regalis specimens were collected. B, magnified map of the grey rectangular region in Fig 1A, showing the localities of the holotype (CMN 2288) and paratype (CMN 2289) of E. regalis. C, stratigraphic subdivision of the Horseshoe Canyon Formation, with the stratigraphic range of E. regalis.
Fig 2
Fig 2. Reconstruction of Edmontosaurus regalis mainly based on CMN 2288, CMN 2289, CMN 8399, and UALVP 53722 (modified from Campione and Evans [8]).
Fig 3
Fig 3
Incomplete cranium of Edmontosaurus regalis (CMN 2288) in left lateral (A, B) and dorsal (C, D) views; photographs (left) and line drawings (right).
Fig 4
Fig 4. Close-ups of the cranium of Edmontosaurus regalis (CMN 2288).
A, left laterodorsal view of the snout. B, anterodorsal view of the snout. C, left laterodorsal view of the skull roof. D, left anterolateral view of the posterior half of the skull. E, posterior view of the skull. F, left anterolateral view of the neurocranium through the orbit. The prominent postorbital pocket is indicated by a red arrow.
Fig 5
Fig 5
Left and right maxillae of Edmontosaurus regalis (CMN 2289) in lateral (A, B), medial (C, D), dorsal (E, F), and ventral (G, H) views.
Fig 6
Fig 6
Articulated left maxilla, palatine and ectopterygoid, and articulated right maxilla, palatine and ectopterygoid of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views.
Fig 7
Fig 7
Articulated left nasal, prefrontal, lacrimal and frontal, and articulated right nasal, prefrontal, lacrimal and frontal of Edmontosaurus regalis (CMN 2289) in lateral (A, B), medial (C, D), dorsal (E, F), ventral (G, H), and posterior (I, J) views.
Fig 8
Fig 8
Left and right jugals of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views. Close-ups of the jugal anterior process of CMN 2288 in lateral (E) and posterolateral (F) views. Left and right quadratojugals of Edmontosaurus regalis (CMN 2289) in lateral (G, H) and medial (I, J) views. The sharp posterolateral projection of the jugal along the orbital margin is indicated by an arrow.
Fig 9
Fig 9
Left quadrate of Edmontosaurus regalis (CMN 2289) in lateral (A), medial (B), anterior (C), and posterior (D) views.
Fig 10
Fig 10
Partial, articulated skull roof and neurocranium of Edmontosaurus regalis (CMN 2289) in dorsal (A, B) and ventral (C, D) views; photographs (left) and line drawings (right).
Fig 11
Fig 11
Partial, articulated skull roof and neurocranium of Edmontosaurus regalis (CMN 2289) in left lateral (A, B) and right lateral (C, D) views; photographs (left) and line drawings (right).
Fig 12
Fig 12
Partial, articulated skull roof and neurocranium of Edmontosaurus regalis (CMN 2289) in anterior (A, B) and posterior (C, D) views; photographs (left) and line drawings (right). The well-developed postorbital pocket is indicated by an arrow.
Fig 13
Fig 13
Left and right ectopterygoids of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views. Left and right palatines of Edmontosaurus regalis (CMN 2289) in lateral (E, F), medial (G, H), and anterior (I, J) views.
Fig 14
Fig 14
Left and right pterygoids of Edmontosaurus regalis (CMN 2289) in anterolateral (A, B) and posteromedial (C, D) views.
Fig 15
Fig 15
Anterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left anterolateral (A) and right anterolateral (B) views. Posterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left lateral (C) and right lateral (D) views.
Fig 16
Fig 16
Left and right dentaries of Edmontosaurus regalis (CMN 2289) in lateral (A, B), medial (C, D), dorsal (E, F), ventral (G, H), and posterior (I, J) views.
Fig 17
Fig 17
Incomplete, articulated right dentary, surangular, angular, splenial and articular of Edmontosaurus regalis (CMN 2288) in lateroventral (A), dorsomedial (B), dorsal (C), and ventral (D) views.
Fig 18
Fig 18
Incomplete, articulated right surangular and angular of Edmontosaurus regalis (CMN 2289) in lateroventral (A), dorsomedial (B), and dorsal (C) views. Incomplete left angular of Edmontosaurus regalis (CMN 2289) in laterodorsal (D) and ventromedial (E) views. Partial right splenial of Edmontosaurus regalis (CMN 2289) in lateral (F), medial (G), and dorsal (H) views. Nearly complete, articulated left splenial and articular of Edmontosaurus regalis (CMN 2289) in lateral (I), medial (J), and dorsal (K) views.
Fig 19
Fig 19. Dentitions of Edmontosaurus regalis (CMN 2289).
Exposed teeth in the middle of the left maxilla in labial (A) and occlusal (B) views. Exposed teeth in the middle of the left dentary in lingual (C) and occlusal (D) views. Positions of active teeth on the occlusal surface are indicated by blue arrows.
Fig 20
Fig 20. Strict consensus of 24 most parsimonious trees resulting from the maximum parsimony analysis of Hadrosauroidea, showing the sister-group relationship between Hadrosaurinae and Lambeosaurinae within Hadrosauridae.
Numbers above lines represent bootstrap proportions, whereas those below lines represent Bremer decay values. Bootstrap proportions lower than 20 and Bremer decay values less than 2 are not shown.
Fig 21
Fig 21. Time-calibrated cladogram of Hadrosaurinae derived from the strict consensus tree shown in Fig 20, with probability estimation of ancestral continental regions for all nodes of the taxon.
Blue stars indicate hadrosaurine species recovered from Appalachia, eastern North America.
See this image and copyright information in PMC

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