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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.


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.
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pone.0175253.g013: 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.

Mentions: Ectopterygoid (Figs 6 and 13). The ectopterygoid is a dorsoventrally flattened bone that comprises a long anterior ramus and a pair of tongue-like posterior flanges. This element is best preserved but partially reconstructed with plaster in CMN 2289. The anterior ramus covers most of the dorsal surface of the ectopterygoid shelf as it gradually narrows mediolaterally towards the external naris. This ramus is proportionately broader than in Maiasaura and Brachylophosaurus. A rimmed, subtriangular eminence adjacent to both the anterior ramus and posterodorsal flange projects medially from the dorsomedial margin of the ectopterygoid. When in articulation, the eminence is tightly locked between the pterygoid process of the maxilla anterodorsally and the posterior part of the ectopterygoid shelf ventrally, and is posteriorly and medially buttressed by the pterygoid. The posteromedial surface of the entire posterodorsal flange, together with the medial surface of the posterior half of the posteroventral flange, constitutes a gently concave, auriform sutural surface for the pterygoid.


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

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

pone.0175253.g013: 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.
Mentions: Ectopterygoid (Figs 6 and 13). The ectopterygoid is a dorsoventrally flattened bone that comprises a long anterior ramus and a pair of tongue-like posterior flanges. This element is best preserved but partially reconstructed with plaster in CMN 2289. The anterior ramus covers most of the dorsal surface of the ectopterygoid shelf as it gradually narrows mediolaterally towards the external naris. This ramus is proportionately broader than in Maiasaura and Brachylophosaurus. A rimmed, subtriangular eminence adjacent to both the anterior ramus and posterodorsal flange projects medially from the dorsomedial margin of the ectopterygoid. When in articulation, the eminence is tightly locked between the pterygoid process of the maxilla anterodorsally and the posterior part of the ectopterygoid shelf ventrally, and is posteriorly and medially buttressed by the pterygoid. The posteromedial surface of the entire posterodorsal flange, together with the medial surface of the posterior half of the posteroventral flange, constitutes a gently concave, auriform sutural surface for the pterygoid.

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.