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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.


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.
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pone.0175253.g019: 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.

Mentions: Maxillary teeth (Figs 3–6 and 19). The left and right maxillae in CMN 2289 possess 53 and 51 alveoli, respectively. Only active teeth along the occlusal surface are recognizable in CMN 2289 because replacement teeth of the dental battery are entirely obscured from view by the thin medial parapet of the maxilla. In the middle dental battery, most of the occlusal surface is formed by two functional teeth per alveolus, namely a worn crown and a residual, more medially situated root. A small minority of alveoli along the middle part of the dental battery hold a single functional tooth for each position, which is applied to most of the alveoli along the anterior and posterior regions of the battery. The enameled labial surface of each tooth crown is diamond-shaped and evenly separated by a straight primary ridge. The mesial and distal margins of the apical half of the surface is poorly denticulated, contrasting with the large mammillate denticles seen in Brachylophosaurini. Of note, the maxillary tooth crowns of CMN 2289 are mesiodistally narrower and apicobasally shorter than the dentary ones. The tooth crown in the middle of the maxilla measures 8 mm in average maximum width, and has an estimated height of 29 mm.


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

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

pone.0175253.g019: 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.
Mentions: Maxillary teeth (Figs 3–6 and 19). The left and right maxillae in CMN 2289 possess 53 and 51 alveoli, respectively. Only active teeth along the occlusal surface are recognizable in CMN 2289 because replacement teeth of the dental battery are entirely obscured from view by the thin medial parapet of the maxilla. In the middle dental battery, most of the occlusal surface is formed by two functional teeth per alveolus, namely a worn crown and a residual, more medially situated root. A small minority of alveoli along the middle part of the dental battery hold a single functional tooth for each position, which is applied to most of the alveoli along the anterior and posterior regions of the battery. The enameled labial surface of each tooth crown is diamond-shaped and evenly separated by a straight primary ridge. The mesial and distal margins of the apical half of the surface is poorly denticulated, contrasting with the large mammillate denticles seen in Brachylophosaurini. Of note, the maxillary tooth crowns of CMN 2289 are mesiodistally narrower and apicobasally shorter than the dentary ones. The tooth crown in the middle of the maxilla measures 8 mm in average maximum width, and has an estimated height of 29 mm.

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.