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

View Article: PubMed Central - PubMed

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.

No MeSH data available.


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.
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pone.0175253.g018: 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.

Mentions: Surangular (Figs 3, 4, 17 and 18). The surangular morphology of Edmontosaurus regalis closely resembles that of other hadrosaurines: the posterior half of the element is dorsoventrally shortened, with a strongly ventrally twisted dorsolateral flange and a nearly straight, posteriorly directed retroarticular process. The anterior half of the surangular is markedly dorsomedially excavated by the posterior region of the mandibular adductor fossa that has a deeply arcuate edge contour, and is laterally shaped by a mediolaterally thin, ascending anterodorsal process. The anterodorsal process occurs directly dorsal to the posterior region of the mandibular adductor fossa. The posteromedial margin of the former is continuous posteroventrally with the dorsal edge of the latter. In articulated mandibles, including CMN 2288, most of the lateral surface of the anterodorsal process is concealed by the lateral wall of the triangular depression on the posterior surface of the dentary coronoid process, very similar to the condition in other hadrosaurids. By contrast, in many basal hadrosauroids such as Equijubus normani (IVPP V12534), only the anterior half of the anterodorsal process is laterally covered by the depressed posterior part of the coronoid process when in articulation.


Supplementary cranial description of the types of Edmontosaurus regalis (Ornithischia: Hadrosauridae), with comments on the phylogenetics and biogeography of Hadrosaurinae
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.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383305&req=5

pone.0175253.g018: 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.
Mentions: Surangular (Figs 3, 4, 17 and 18). The surangular morphology of Edmontosaurus regalis closely resembles that of other hadrosaurines: the posterior half of the element is dorsoventrally shortened, with a strongly ventrally twisted dorsolateral flange and a nearly straight, posteriorly directed retroarticular process. The anterior half of the surangular is markedly dorsomedially excavated by the posterior region of the mandibular adductor fossa that has a deeply arcuate edge contour, and is laterally shaped by a mediolaterally thin, ascending anterodorsal process. The anterodorsal process occurs directly dorsal to the posterior region of the mandibular adductor fossa. The posteromedial margin of the former is continuous posteroventrally with the dorsal edge of the latter. In articulated mandibles, including CMN 2288, most of the lateral surface of the anterodorsal process is concealed by the lateral wall of the triangular depression on the posterior surface of the dentary coronoid process, very similar to the condition in other hadrosaurids. By contrast, in many basal hadrosauroids such as Equijubus normani (IVPP V12534), only the anterior half of the anterodorsal process is laterally covered by the depressed posterior part of the coronoid process when in articulation.

View Article: PubMed Central - PubMed

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.

No MeSH data available.