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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 dentary, surangular, angular, splenial and articular of Edmontosaurus regalis (CMN 2288) in lateroventral (A), dorsomedial (B), dorsal (C), and ventral (D) views.
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pone.0175253.g017: 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.

Mentions: Dentary (Figs 3, 4, 16 and 17). Both the left and right dentaries are well preserved in CMN 2289, although the right one appears to be slightly distorted due to post-depositional dorsoventral crushing. The anterior part of the dentary ramus is gently anteroventrally deflected, forming an angle of 14° with the horizontal posterior part of the ramus. In comparison, the ventral deflection of the dentary anterior part is much stronger in Kritosaurus (e.g. AMNH 5799) and Gryposaurus (e.g. ROM 873), with a relatively steep dorsal contact surface for the predentary. Posterior to the symphysial process, the edentulous region of the dentary in CMN 2289 is approximately 38% as long as the tooth row. In fact, the ratio between the length of the edentulous region and that of the tooth row varies significantly among the adult dentaries of Edmontosaurus regalis, ranging from 0.34 to 0.50. The dentary has an anteroposteriorly elongate, subelliptical tooth row, the lingual surface of which is slightly anteroposteriorly and dorsoventrally convex. The tooth row bears 48 vertical tooth positions and a transversely narrow, dorsolaterally concave occlusal surface. In medial view, the long axis of the tooth row parallels the ventromedial margin of the middle part of the dentary ramus. This condition contrasts with the modestly anterodorsally inclined long axis of the tooth row in Acristavus gagslarsoni (e.g. MOR 1155) and Probrachylophosaurus bergei (MOR 2919). The tooth row extends slightly posterior to the coronoid process. As in all other hadrosaurines except Brachylophosaurini, the apex of the coronoid process in E. regalis is subcircular and anteroposteriorly expanded, with a pronounced posterior extension. The buccal shelf between the base of the coronoid process and the posterior end of the tooth row is mediolaterally broad and deeply depressed. Posteriorly, the anterior region of the mandibular adductor fossa becomes progressively narrower and shallower towards the apex of the coronoid process.


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

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

pone.0175253.g017: 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.
Mentions: Dentary (Figs 3, 4, 16 and 17). Both the left and right dentaries are well preserved in CMN 2289, although the right one appears to be slightly distorted due to post-depositional dorsoventral crushing. The anterior part of the dentary ramus is gently anteroventrally deflected, forming an angle of 14° with the horizontal posterior part of the ramus. In comparison, the ventral deflection of the dentary anterior part is much stronger in Kritosaurus (e.g. AMNH 5799) and Gryposaurus (e.g. ROM 873), with a relatively steep dorsal contact surface for the predentary. Posterior to the symphysial process, the edentulous region of the dentary in CMN 2289 is approximately 38% as long as the tooth row. In fact, the ratio between the length of the edentulous region and that of the tooth row varies significantly among the adult dentaries of Edmontosaurus regalis, ranging from 0.34 to 0.50. The dentary has an anteroposteriorly elongate, subelliptical tooth row, the lingual surface of which is slightly anteroposteriorly and dorsoventrally convex. The tooth row bears 48 vertical tooth positions and a transversely narrow, dorsolaterally concave occlusal surface. In medial view, the long axis of the tooth row parallels the ventromedial margin of the middle part of the dentary ramus. This condition contrasts with the modestly anterodorsally inclined long axis of the tooth row in Acristavus gagslarsoni (e.g. MOR 1155) and Probrachylophosaurus bergei (MOR 2919). The tooth row extends slightly posterior to the coronoid process. As in all other hadrosaurines except Brachylophosaurini, the apex of the coronoid process in E. regalis is subcircular and anteroposteriorly expanded, with a pronounced posterior extension. The buccal shelf between the base of the coronoid process and the posterior end of the tooth row is mediolaterally broad and deeply depressed. Posteriorly, the anterior region of the mandibular adductor fossa becomes progressively narrower and shallower towards the apex of the coronoid process.

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.