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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.


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.
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pone.0175253.g012: 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.

Mentions: Squamosal (Figs 3, 4 and 10–12). The squamosal is a quadradiate, laterodorsally bowed bone that comprises the posterolateral corner of the supratemporal fenestra and the medioventral half of the intertemporal bar. As in other hadrosaurines, the central region of the squamosal is not drastically elevated relative to the neurocranium. The anterior half of the element is laterodorsally overlapped by the postorbital, where an extremely narrow band of the squamosal is dorsally exposed and forms part of the lateral margin of the supratemporal fenestra. In ventral view, a short, mediolaterally compressed process extends anteriorly from the central region of the squamosal, to meet the base of the jugal process of the postorbital. The quadrate cotylus is deep and suboval, and has a parasagittal long axis. This cotylus is slightly posteroventrally inclined, forming an angle of 20° with the dorsal side of the skull roof. Just below the postorbital-squamosal joint, there is a deep, strongly constricted precotyloid fossa that tapers posterodorsally and medially. The fossa limits the anteroventrally and slightly laterally directed, subconical precotyloid process anterodorsally. The precotyloid process is subtriangular in cross-section. It is proportionally shorter than that in Prosaurolophus (e.g. ROM 787), Lophorhothon (FMNH P27383), Kritosaurus (e.g. NMMNH P-16106), and Gryposaurus (e.g. AMNH 5350). The postcotyloid process is anteroposteriorly broad and anteroventrally curved. The process overlaps the ventral half of the exoccipital paroccipital process laterodorsally along its posterolateral region.


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

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

pone.0175253.g012: 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.
Mentions: Squamosal (Figs 3, 4 and 10–12). The squamosal is a quadradiate, laterodorsally bowed bone that comprises the posterolateral corner of the supratemporal fenestra and the medioventral half of the intertemporal bar. As in other hadrosaurines, the central region of the squamosal is not drastically elevated relative to the neurocranium. The anterior half of the element is laterodorsally overlapped by the postorbital, where an extremely narrow band of the squamosal is dorsally exposed and forms part of the lateral margin of the supratemporal fenestra. In ventral view, a short, mediolaterally compressed process extends anteriorly from the central region of the squamosal, to meet the base of the jugal process of the postorbital. The quadrate cotylus is deep and suboval, and has a parasagittal long axis. This cotylus is slightly posteroventrally inclined, forming an angle of 20° with the dorsal side of the skull roof. Just below the postorbital-squamosal joint, there is a deep, strongly constricted precotyloid fossa that tapers posterodorsally and medially. The fossa limits the anteroventrally and slightly laterally directed, subconical precotyloid process anterodorsally. The precotyloid process is subtriangular in cross-section. It is proportionally shorter than that in Prosaurolophus (e.g. ROM 787), Lophorhothon (FMNH P27383), Kritosaurus (e.g. NMMNH P-16106), and Gryposaurus (e.g. AMNH 5350). The postcotyloid process is anteroposteriorly broad and anteroventrally curved. The process overlaps the ventral half of the exoccipital paroccipital process laterodorsally along its posterolateral region.

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.